Excessive Oil Consumption or simply a little blue smoke at startup & the Top-End Rebuild - This is a procedure 993/964 owners are asked to consider by enterprising mechanics. It is made under the conclusion that the valve guides are worn to the point that excessive oil is slipping past them and burning. Oil consumption and or blue smoke at startup alone is never an indication of the need for a top-end rebuild. Blue smoke at a startup usually has to do with oil vapor from the oil tank condensing on the inside of the intake manifold and being drawn into the engine at startup and burning, a perfectly normal condition.
A recent posting on Facebook in a Porsche 993 Group:"I’m getting blue exhaust when I start the car. My mechanic says it’s a $15 k fix."
I recently ran across the following comment in a 993 technical forum in reply to an oil consumption concern:
The implication here is that a true measure of a full oil tank is somewhat variable and frequent overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the ingested overfill explain blue smoke at startup or over time misfire problems or clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Seems a lot more feasible as the common root cause than leaking valve stems.
“How full do you keep the oil tank? When I kept mine at the full level [on the dipstick] I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 [of the range on the dip stick] I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full [on the dash gauge].”
The implication here is that a true measure of a full oil tank is somewhat variable and frequent overfilling may be contributing to the perception of excessive oil consumption where none may exist. Could burning the ingested overfill explain blue smoke at startup or over time misfire problems or clogged secondary air injector ports, potentially a self-inflicted service issue caused by simply overfilling the oil? Seems a lot more feasible as the common root cause than leaking valve stems.
Here is a little more information on diagnosing the need for a top-end rebuild.
Here is a primer on how to read and interpret the oil-related dash gauges in a 993.
I change my own oil - Here is the oil fill procedure I use today to
address the whole overfill conundrum, use it at your own risk as I am not a professional automotive technician. If you have any concerns about aspects of the procedure contact a professional for their advice.
I change my own oil - Here is the oil fill procedure I use today to
address the whole overfill conundrum, use it at your own risk as I am not a professional automotive technician. If you have any concerns about aspects of the procedure contact a professional for their advice.
- If your car still has the under-engine cover/tray remove it and store it away as some folks think it just hides oil leaks and causes the engine to retain heat. I feel it serves little purpose beyond making changing the oil more difficult. It has gone missing on most examples of a 993.
- Park the car on level ground & engage the parking brake
- Break free the right rear wheel's nuts and leave them slightly snug this being the passenger side of USA-delivered cars. The right side of the car is on the right-hand side when you are standing behind the car looking forward. If you use LIFTBARS to lift your car it may be necessary to remove the entire rocker panel cover strip before lifting the car so it doesn't interfere with getting to the oil tank.
- lift the right rear wheel off the ground and put it on a jack stand. To safely lift a 993/964 a DIY procedure can be found at Jacking Up A 993 Safely
- Remove the right rear wheel and the front half of the wheel well liner and release the back half of the plastic rocker panel cover strip.
- There is a rearmost special clip that holds the rocker pannel strip in place on a 993. Many times it is broken and can be replaced if needed. On the 993 Carrera, it is a 999.507.373.00 for wide-body 993 cars it is a 999.591.990.00
- I drain the oil tank and the engine case into a drain pan of at least 10 to 12 quarts in capacity. Do not attempt to drain the oil using a vacuum oil remover through the oil filler neck, it will not work and can easily damage or bend the oil level float arm in the oil tank or puncture the filler hose to the tank. The engine case drain plug is on the bottom of the engine case and points to the left side of the car.
Flapper Valve Housing - I reach under the car through the right rear wheel well, and I replace both filters. This requires removing Phillips screws, hex screws, and plastic hex flange nuts holding the back half of the fender liner, and the back half of the plastic rocker panel cover strip.
- I then detach the forward-facing red rubber duct from the heating system flapper valve housing (diverter), hanging below the engine, and tuck the duct out of the way.
- I use large Channel-Locks pliers to initially break loose both the small and large filters. Removing the small filter will be messy, cleaning up after installing the new filter is discussed later in the process. When installing the new filters I rub a little old oil on the rubber seals on the filters before threading them in place. I make both replacement filters as tight as I can with my bare hands and then turn the filter a quarter-turn beyond this with the pliers. Although not a factory method I have never encountered a filter backing off or being unable to remove one with this method.
- The oil filters are:
- 993-107-203-05* for the small filter;
- 993-207-201-03 for the large one.
*If you use an aftermarket branded filter such as MAHLE, BOSCH, or others on the Turbo model be sure to use one that incorporates an internal anti-drain back check valve like the OE filter. Generally, the aftermarket small filter part number crosses to a 993-107-203-03 Porsche part number, and then one of the premium series in that brand under that cross includes the internal check valve. In most cases, the check valve can be seen through the small oil passageway holes in the bottom of the filter when it is compared to one without the valve. The valve is thought to minimize smoking at startup.
Filter's internal
anti-drain back
check valve- Because of ready availability and low cost after rebate, I use Mobil 1-FS 0W-40, and in warmer climates or if you see your oil pressure gauge regularly dip below 2 Bar at idle under normal operation some switch to the Mobil 1-FS X2 5W-50 grade. Both of these oils have slightly higher zinc levels of 1100 parts per million which is thought to help extend the life of the valve train in our cars' engines. Other brands with similar published specifications will work just as well. Oil recommendations can be a rancorous discourse in our community, my answer to this is to each their own.
- I do not disconnect the rigid metal oil tube below and slightly to the rear of the smaller filter on the engine case even though it is specified in the factory procedure. My belief is that breaking the seal on the tube presents an unnecessary leak failure mode and the quantity of oil present in the lines is small. Also, others have found removing a tube that is not removed regularly can be problematic resulting in it being damaged and needing to be replaced, a real pain to do.
- I do keep two cans of spray electronic parts cleaner on hand to clean off oil spilled on the engine, suspension, and the flapper valve & duct from removing the smaller filter.
- When replacing the engine case and oil tank plugs I replace the crush rings and the "O" ring on the tank plug.
Crush Rings - The part number for the oil tank drain plug crush ring is 900.123.118.30 and seems to have critical dimensions so the dealer part should be used.
The engine case drain plug for the MY1995 and earlier is 900.123.118.30 and for MY1996 and later cars, it is 900.123.011.30. The part numbers seem to be interchangeable as they are described as the same A-22mm ID x27mm OD size and are made of aluminum.Oil Tank
Drain Plug
O-Ringg- The heat-resistant Viton oil tank drain plug part number 999.701.269.40 is sized at 11x2.5.
- On occasion, I have reused the existing metal crush rings and heat-resistant "O" ring with no leaks. Be sure not to overtighten the tank plug, both the engine case and oil tank drain plugs are to be tightened to 50Nm (+5/-0 tolerance) or 36.9 ft-lb (+3.7/-0) according to the factory. A lifetime supply of the A22x27 aluminum crush rings and the heat-resistant 11x2.5 Viton (Fluorine rubber) green O-Rings, for the tank plug can be had on eBay or Amazon for a few dollars.
- Button up the plastic parts, and the heating duct, mount the wheel and lightly snug the wheel nuts, then put the car back on the ground.
- Re-torque the wheel nuts to the recommended dry thread value of 133Nm. or 98 ft./lb. (dry) in a cross-wheel star pattern sequence, then check the torque values by repeating the sequence on the now-tightened wheel nuts.
- Refill the oil tank very slowly using a long neck funnel so the oil does not back up in the funnel or in the oil filler pipe's neck and spills out over the top and all over the place.
- Stuff some rags around the filler neck to catch any incidental overflow.
- Running the engine for a few moments once six or seven quarts have been added charging the oil filters seems to reduce the tendency for the oil to back up when filling the oil tank further.
- Spilled oil is hard to clean up completely and many times shows up days if not weeks later under the car where it is misdiagnosed as a leaking lower right valve cover, go figure?
Long Neck
Funnel - Fill with 8 quarts +/- of oil and run the engine to a fully warmed state. This can take a 20-minute drive to achieve, looking to the temperature and oil pressure gauges to see if they have settled into their normal operating range.
- Then, with the engine, still running, add additional oil, a few ounces at a time until oil registers on the dip-stick at approximately 1/4 to1/3 of its scale
with the car on level ground.
Dip-stick - The oil fill difference between the top and bottom of both the dipstick and the gauge is rather small so take your time adding oil in small increments while rechecking the dipstick.
- If you find yourself putting ten or more quarts of oil in, using this procedure, you are most likely overfilling the engine. On a 993/964 this can have serious operating consequences and so an over-fill should be addressed as soon as possible. The easiest way to address an over-fill is to shut off the engine and drain the oil from the engine case as the case retains a smaller volume of oil, most of the oil is retained in the oil tank. Once drained, it can be added back in, if needed, to readjust the level.
If you are having a shop change your oil for you:
As of late I have heard of incidents where a Porsche specialty service shop has overfilled the oil. This seems to suggest properly adjusting the oil level in a 993/964 is not universally understood even in the professional Porsche servicing community. Knowing this it may be best when having your 993's oil changed to specify that the technician only put 8 quarts in and no more. Then once you have driven your car home personally adjust the final fill level in your driveway.
If you suddenly experience what appears to be an oil leak shortly after an oil change by others here are the probable causes.
The final steps I have added with each oil change are to;
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| Fanbelt Switch |
- Put a very small dab of white lithium grease on the center of the side (hub) of the wheel of the fanbelt switch roller. Over time this grease will migrate into the bearing greatly extending its life and so the switch's as well.
- Pull off the ignition distributor caps and rotors and place a drop or two of motor oil on the center of the shafts under each rotor and the mechanism under the doughnut-shaped plastic spark shield over the mechanism below. This will lubricate and help avoid corrosion forming in the distributor mechanism potentially extending its life considerably. Many forgo this procedure for long periods as the service intervals for the distributor caps are quite long on a 993/964. In the old pre-electronic ignition days when ignition points were changed or adjusted every 1500 miles, adding a drop or two of oil was a standard add-on procedure.
Special considerations for the 993 Turbo Variant and smoking at startup:
Although some folks feel a little smoke at strtup is a big problem, an ocasional plume of smoke at startup especially if the car has been sitting for a while is normal for these cars, and should be of no great concern. In any event, if the smoking still bothers you there are options to potentially minimize oil smoking at startup on the Turbo 964/993.
One theory is when at rest some oil may backflow into the turbo lubricating system and can cause a small quantity of oil to leak internally to the turbos. This oil will burn at startup making for a blue plume of smoke. Some argue that this is not plausible because at startup the turbos are cold and any oil present will not be hot enough to initially burn and cause immediate smoking. Another theory is that oil vent hoses leading from the turbo and or the oil tank to the intake discharge a small amount oil vapor that condenses on the inside of the intake manifold and this oil is immediatly injested and burns at start-up causing the plume. In any event here is what some have done to minimize smoking at startup.
- Switching to a heavier weight (20W-50W Multigrade) oil,
- Verifying the oil filters used have the internal valving to limit the back-flow such as the Porsche branded Turbo filters and;
- Making sure the oil is not overfilled (lower 1/3 of dipstick).
- There is an aftermarket oil inlet check valve
that addresses oil migration from the oil tank to the engine. There are also aftermarket check valve kits some add to the oil feed lines of the turbochargers. I hear that some adapt the 996 Turbo Oil Feed Line Check Valve 99610703079 for use on a 993 as well.
I feel the above oil filling method gives an additional margin of safety in avoiding inadvertently overfilling the 993 with oil. If you decide to follow my measurement procedure and as a follow-up check the fill with the dash gauge and your gauge doesn’t read at about 1/3 of its range the float in the oil tank is a bit out of adjustment. Adjusting the float so the gauge approximately matches the dipstick involves draining the oil tank accessing the oil float in the tank and bending its arm a little. I have done this on my 86’ Carrera and have been told it is not too difficult on the 964/993. If you want to make the adjustment it is something to consider at your next oil change when the tank is drained.
A situation I had with my 86” Carrera and now some have reported the same issue with the 993 is where untrained hands mistakenly remove the cover of one of the
oil pressure relief valves, items "A" & "B" in the illustration to the right, rather than the oil drain plug on the bottom of the engine case when attempting to drain the oil. If the oil pressure valve relief cover is replaced without first reinstalling the spring/components it retains your engine will immediately have serious lubrication issues. If you happen to open the wrong cap and see some small parts under it, just put it back on with the parts in the same way. Then look for the other cap, the correct one, at the bottom edge of the engine case with its hex plug facing the left side, the driver’s side of the car on USA-delivered cars, to drain your oil. If your car comes back from an oil change with the oil pressure warning light illuminated and or the oil pressure near zero stop driving the car immediately and address the missing oil pressure valve parts that most likely fell into the oil drain pan unnoticed.
A situation I had with my 86” Carrera and now some have reported the same issue with the 993 is where untrained hands mistakenly remove the cover of one of the
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| Relief valve locations. |
Internal Engine Repairs:
I’m going out on a limb a bit, But I feel any road-driven normally aspirated 993 (Carrera) that has been used exclusively for street driving and an occasional club auto-cross should not need any internal engine work beyond replacement valve lifter cartridges until well beyond 150,000 miles. At this point and over the last 27 years some owners have managed to run their cars up in excess of 200,000 miles of use without issue. This suggests the need for internal engine work on a street-driven car should always be suspect and the need validated by multiple persons via multiple diagnostic methods.
Oil Leaks. - At some point in your car's life, it will leak oil. The 993/964 engine is oil-cooled and lubricated and the engine itself, unlike others is a vast assemblage of heads, cylinders, case haves, valve covers, oil coolers, and the oil tank, and the list goes on. One can spend a lot of time and money chasing minor oil leaks an expense that contributes little to the driving enjoyment of these cars. In my book, the main reason to fix an oil leak is that it is dripping on the floor and that bothers you or it is dripping on the exhaust and smells bad. Small leaks other than these or oil wetness on the engine case are best not bothered with.
Seeing that these cars are over +26 years old and many have well over 100K miles on them valve cover sealing gaskets seem to be the most common source of an oil leak. If the gasket is replaced properly, the valve covers shouldn't be problematic for a very long time. The gasket is relatively inexpensive to have replaced. I find it not to be a fun DIY job gaining access to the mounting capscrews to remove and reinstall the covers so I leave it to the professionals to do. There are 4 covers & gaskets and there is no need to replace any gasket other than the one that has proven to be leaking. Replacing all 4 at once is a common stealth up-sell that adds unnecessary expense.
Oil Leaks. - At some point in your car's life, it will leak oil. The 993/964 engine is oil-cooled and lubricated and the engine itself, unlike others is a vast assemblage of heads, cylinders, case haves, valve covers, oil coolers, and the oil tank, and the list goes on. One can spend a lot of time and money chasing minor oil leaks an expense that contributes little to the driving enjoyment of these cars. In my book, the main reason to fix an oil leak is that it is dripping on the floor and that bothers you or it is dripping on the exhaust and smells bad. Small leaks other than these or oil wetness on the engine case are best not bothered with.
Interestingly I thought my car had two oil leaks one at one of the cylindar head oil return tubes. The other appeared to be on the passenger side lower valve cover dripping on the heat exchanger and smelling up the car, I am told a very common occurrence. I researched a DIY valve cover gasket replacement and it seemed simple enough. I went ahead and purchased the new gasket. In preparation, I cleaned the oil off the valve cover and the exhaust using spray electronic cleaner. Afterward, the leak seemingly disappeared. Then I recalled that at my last oil change I spilled a little oil when filling the engine. I wiped up most of it and hosed off the remainder I could see with the electronic parts cleaning spray. Apparently, it took weeks for unseen oil to migrate to the valve cover and ultimately onto the exhaust.
In retrospect, I wonder how many valve cover gasket or even valve cover replacements have been done on a 993 due to a botched oil change where cleaning was all that was needed. If you are experiencing a leak from what appears to be the lower right-hand valve cover just clean it off with some spray electronic cleaner first and see if it resolves the leak. Also if you are experincing what appers to be an oil leak after a recent oil change here is a page describing the potential root causes.
Valve Covers:
Quite regularly I hear about the desire to replace the plastic valve covers because they leak or could be warped. Turns out if one looks at the design of the gasket shown below it surrounds each mounting bolt isolating them from the sealing function and is a three-dimensional synthetic rubber material. When used in conjunction with the cover it becomes clear that the sealing process is designed so any aspect of what might be leaking is replaced when the gasket is replaced. As far as warping goes the covers are a lot softer than the head and are held down by quite a few fasteners warping, if even possible, really is not an issue.
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| Valve Cover Gasket |
For these reasons, the valve covers have turned out to have a very long service life, in most cases beyond the life of the car and so there is really no benefit in replacing them. This is why replacing them with aftermarket metal ones has fallen out of favor in the 993 community.
My experience is that one will end up replacing the valve cover gaskets once or twice in the life of the car usually as part of servicing something under the covers such as the hydraulic lifter adjusting cartridges. I have a theory that in some cases valve cover leaks are the result of removing the valve covers for other reasons or because of an oil change spill that was misdiagnosed as a valve cover leak and subsequently the new gaskets do not get properly installed. This results in a future leaking problem a few thousand miles later. Part of this theory is that I doubt most technicians use a torque wrench to ensure the cover capscrews are tensioned properly simply because there isn't the clearance needed to fit such a wrench without the disassembly of other components.
A Porsche technician once told me that if properly installed the 993 valve covers rarely leak. He informed me that leaks are usually the result of under-torquing the mounting bolts, the factory spec. is 9.7NM, or tightening them up in the wrong order. My understanding is the correct order is from the center out, alternating between the top and bottom of the cover although I have not been able to get validation in a factory document for this. I suspect the torque value and the tightening sequence are available from Porsche if one was to ask at a dealer.
When replacing the valve cover gaskets some have also found using Elring Curil T Liquid Gasket non-hardening, temperature-resistant sealing compound in conjunction with new gaskets seems to do a good job of resolving leaks.
Oil leak on the underside of the Varioram intake:
Another common source of an oil leak is from the underside
of the intake manifold on the Varioram-equipped cars. Oil vapor from the crankcase/oil tank is vented to the intake of the engine, one of the very first emission control measures put on vehicles in the early 1960s and continues to this day. The intake manifold is metal and is a lot cooler in many cases than the vapor so it condenses onto the inside of the manifold before it can be ingested into the engine and burned off.
Oil leak on the underside of the Varioram intake:
Another common source of an oil leak is from the underside
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| Leak Location, Underside of Varioram |
of the intake manifold on the Varioram-equipped cars. Oil vapor from the crankcase/oil tank is vented to the intake of the engine, one of the very first emission control measures put on vehicles in the early 1960s and continues to this day. The intake manifold is metal and is a lot cooler in many cases than the vapor so it condenses onto the inside of the manifold before it can be ingested into the engine and burned off.
The condensed oil pools on the downward-facing surfaces inside the manifold. Located on the underside of the manifold is a lever that controls a Varioram valve inside the intake. The seal where it attaches to the manifold's bottom does not reliably seal it off and so a small amount of oil leaks out around it. Replacing the seal some would consider an expensive endeavor involving removing the manifold and disturbing several 25+year-old components that may introduce additional vacuum leaks for a very limited benefit. Although unlikely, some suggest that the leak also can be the source of a small vacuum leak.
Let's face it our cars all have some level of vacuum leaks where the Motronic system can to some extent adjust for them and if really a problem operating symptoms would appear or even a Check Engine Light would illuminate. For this reason, I would call a small oil leak here inherent in the design of the engine, and in absence of other symptoms where it is verified as a contributing factor, no action should be taken. Sometimes a problem is only a problem because one keeps thinking of it as such.
Let's face it our cars all have some level of vacuum leaks where the Motronic system can to some extent adjust for them and if really a problem operating symptoms would appear or even a Check Engine Light would illuminate. For this reason, I would call a small oil leak here inherent in the design of the engine, and in absence of other symptoms where it is verified as a contributing factor, no action should be taken. Sometimes a problem is only a problem because one keeps thinking of it as such.
Now for something completely different:
Here is an interesting posting I recently found on Rennlist:
"I [purchased] a 97 C4S that was leaking oil (chain boxes, base gaskets, etc) after basically sitting for 18 mos (~500 miles in 2 yrs). "Drove it every day for a month and voila...all but 1 of the oil leaks stopped"
The above posting seems to suggest that just exercising an engine may cause leaks formed while standing for long periods to diminish if not resolve themselves completely
Oil Filler Bellows Removal – At this point, it is unlikely that the oil filling bellows is still nestled inside the engine oil filler neck on any 993. It originally was
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| Filler Bellows removed |
Body fluids, Andy’s opinion:
Oil - I have always used Mobil 1. Although it is called synthetic technically it is not,
it is made from a petroleum base stock but it has been extensively processed to remove the bulk of the naturally occurring substances, paraffin wax, etc. that must be kept in solution by the additives to avoid sludge. I use Mobil 1 FS 0w-40 or FS X2 5W-50 with the slightly higher ZDDP level of 1100 PPM, as I have come to understand this additive reduces the scuffing of components in the valve train. I do not use racing or motorcycle oils that have very high levels of zinc, 1300~1850 PPM, as I understand, they may shorten the life of the catalytic converters.
Oil - I have always used Mobil 1. Although it is called synthetic technically it is not,
Here is a page discussing how to read the oil-related gauges on a 993 and how it might influence the viscosity grade of oil you may choose to use.
What sold me on Mobil 1 oil was when I first used it on my 86’ Carrera. In Cleveland winters it would take twenty minutes or more for non-synthetic labeled multi-grade oil to warm up enough for the oil pressure gauge to not be pinned at its maximum 5 bar. When I filled the engine with Mobil 1 it took less than 60 seconds from dead cold as well below 32F to fall into the gauge's useful range. Most engine wear, I understand, happens at startup when an engine is not yet warm, the oil is thick and so does not properly lubricate. With Mobil 1 this period is much shorter as indicated by the oil pressure gauge. In retrospect, almost any oil labeled as fully synthetic will likely result in similar behavior. As a plus, Mobil 1 in the grades needed for a 993 can be ordered online for pickup at Walmart, which works for me. Two 5-gallon jugs cost about $50 and with the Exxon Mobil online rebates, it comes to $26. Then again has anyone, who does not track their car, ever seen a “catastrophic oil-related engine failure” as fear mongered in oil advertisements? If one changes their oil regularly with the OE-recommended brands and viscosities, probably not.
What sold me on Mobil 1 oil was when I first used it on my 86’ Carrera. In Cleveland winters it would take twenty minutes or more for non-synthetic labeled multi-grade oil to warm up enough for the oil pressure gauge to not be pinned at its maximum 5 bar. When I filled the engine with Mobil 1 it took less than 60 seconds from dead cold as well below 32F to fall into the gauge's useful range. Most engine wear, I understand, happens at startup when an engine is not yet warm, the oil is thick and so does not properly lubricate. With Mobil 1 this period is much shorter as indicated by the oil pressure gauge. In retrospect, almost any oil labeled as fully synthetic will likely result in similar behavior. As a plus, Mobil 1 in the grades needed for a 993 can be ordered online for pickup at Walmart, which works for me. Two 5-gallon jugs cost about $50 and with the Exxon Mobil online rebates, it comes to $26. Then again has anyone, who does not track their car, ever seen a “catastrophic oil-related engine failure” as fear mongered in oil advertisements? If one changes their oil regularly with the OE-recommended brands and viscosities, probably not.
Here is a Porsche USA Training Center video about oil:
https://993servicerepair.blogspot.com/2023/01/how-to-keep-your-porsche-engine-running.html
Then Again... Here is what Blackstone Labs, the folks who actually test oils for engine wear say on their website:
"You can go into any mass retailer (Wal-Mart, Meijer, AutoZone, etc.) and buy a 5W/30 (or any other grade) that will perform well in your engine. One of the best-kept secrets of the oil industry is that these store brands are actually the same, quality oils that are produced by the major oil companies. The only difference between these products and the major company brands is the name on the container and the price. Don’t believe us? Try running your own experiment: do a sample on Oil A after a known number of miles, then do a sample on Oil B and compare the wear levels. You may see a little fluctuation, but it’s very rare for one oil to make a significant difference in an engine’s wear patterns."
work as well but is an unnecessary expense. Some folks like to use racing fuels that in some cases have very high Octane ratings. The benefit of these fuels is they generally do not contain any methanol as is typically mixed into pump gas sold in the continental United States. Methanol is referred to as hygroscopic in that it attracts and retains moisture. Over time this moisture will attack the metal components of the fuel system and may contribute to the development of sludge in the fuel system. For daily driver cars this is not an issue but if your car spends a good bit of its life in storage consider a methanol-free fuel, either racing gas or a listing of stations that offer methanol-free pump gas is available through a quick search of the internet.
https://993servicerepair.blogspot.com/2023/01/how-to-keep-your-porsche-engine-running.html
Then Again... Here is what Blackstone Labs, the folks who actually test oils for engine wear say on their website:
"You can go into any mass retailer (Wal-Mart, Meijer, AutoZone, etc.) and buy a 5W/30 (or any other grade) that will perform well in your engine. One of the best-kept secrets of the oil industry is that these store brands are actually the same, quality oils that are produced by the major oil companies. The only difference between these products and the major company brands is the name on the container and the price. Don’t believe us? Try running your own experiment: do a sample on Oil A after a known number of miles, then do a sample on Oil B and compare the wear levels. You may see a little fluctuation, but it’s very rare for one oil to make a significant difference in an engine’s wear patterns."
Quoted from: https://www.blackstone-labs.com/which-oil-to-use/
Porshe Classic branded motor oil:
Lately, Porsche has begun marketing "Porsche Classic" branded motor oil. To be clear Porsche doesn't make motor oil. Porsche is just private branding oil just like auto parts chain stores do. The only difference is that at auto parts stores private branding is part of a lower price point strategy whereas with Porsche it is part of a premium price strategy.
The specifications of motor oil regardless of price strategy are so tightly controlled that branding is not much of an indicator of how one brand over another influences the durability of the engine. As discussed above I use Mobil 1, not because of the brand but because it is readily available, with promotion not expensive and they publish detailed information about each oil they sell such as zinc levels, one of few formulae features that can actually enhance how the oil contributes to engine durability in our cars. I am sure other manufacturers' brands publish this same information if one does a little research and is comparable to Mobil 1.
Fuel Injector & Fuel System Cleaner - I am standing on thin ice as I have only anecdotal support of my opinion concerning this subject.
I hear of issues with clogged fuel injectors and the need to remove and service or replace them from time to time among 993 owners. I have had two electronically fuel-injected Carreras. For the first one, I drove 150K miles without a fuel-related problem. My current 993 has never exhibited an injector problem. I attribute this to treating the engines twice a year with two consecutive tanks of gas where I added Chevron’s Techron fuel system cleaner. My understanding is that Techron, unlike competitive products, will not produce burnt by-product solids as competitive products can if used in high concentrations. Also, Techron is part of the standard additive package used in Shell-branded gasoline and when added in addition to the detergent already present in the fuel helps to remove stubborn carbon deposits. Tests have shown that it takes more than one treated tank of gas with added Techron to make a visible difference in the accumulated burnt fuel byproducts in the engine. As a side note adding this stuff to a hard-to-start Weed Wacker does the trick every time!
Manual Transmission Gear Lubricants:
The additive package used in gear lubricant is specific and serves several related purposes. In normal operation, the sulfur/phosphorous additive forms a black sacrificial
coating on the steel gears. As the gears turn, instead of wearing the steel, the
sacrificial coating of additives is peeled off or worn off. This is normal and acceptable in all steel gears. This is why after a very few miles gear lubricant in our cars turns black and this is not an indication that it needs to be changed. Gear lubricants are produced to specifications the major classes are GL-4 and GL-5. These specifications are not the sole indicator as to how well they work with the synchronizers, metallurgy, or wear characteristics in our car's transmissions. For this reason, always use a brand and grade of lubricant tested and recommended by Porsche or a transmission expert who works extensively with the Getrag G50 Varient synchromesh transmission found in the late-'80s-911/964/993. Be aware these recommendations change over time so look for the latest information before just refreshing your gearbox with its previously filled brand and type of gear oil.
Manual Transmission Gear Lubricants:
The additive package used in gear lubricant is specific and serves several related purposes. In normal operation, the sulfur/phosphorous additive forms a black sacrificial
Why are the synchro teeth rings in our transmissions non-ferrous? This may have to do with the gear oil. If they were steel (ferrous metal) the additives in the oil over time would build up a coating and alter their friction properties altering shifting feel and potentially shifting acceptability. The buildup of a coating from the gear oil additives is not a primary concern for a track car as the transmission is opened up and serviced more often than on a street-driven car. For racing applications steel synchro rings are used, in part, for the racing synchro teeth geometry that provides a stronger positive lock when shifted into each gear. A useful feature under extreme racing conditions but something that can contribute to less than smooth shifting in a street-driven car.
When my transmission was last serviced it became apparent that there was really no wear to be concerned about on the ring teeth anyway. The issue was the loss of the textured facing on the synchro's toothed rings friction facing that engages against a counterpart cone to form the synchro clutch. With wear, the synchro's clutches' facings eventually wear down and do not provide adequate friction to cause gear synchronization and present as gear grinding during shifting.
Here is what the factory says about the gear lubricant change interval:
Some folks change their transmission's gear oil DIY. The cardinal rule to changing the lubricant is to crack open the fill port high on the transmission first before draining the lubricant through the lower drain port. This is to avoid a situation where the oil has been drained and subsequently the filling port is frozen shut resulting in one being stranded with a transmission emptied of lubricant.
Gasoline Octane:
So long as you use fuel with an octane rating as specified in your owner's manual or higher you are good to go, using fuel with an Octane rating higher than needed will
Fueling-Up Smells:
With a 993 "topping off" the gas after the first forced pump nozzle 
click-off will splash fuel in all sorts of places it shouldn't go both in the filling port drain and the venting system. These fumes can persist even after the volume of fuel in the tank has drawn down.
If you have inadvertently overfilled the gas and are experiencing fuel fumes run your car so the fuel gauge is somewhere below pinned on full. Then park your car with the frunk open and the lower hood latch pushed in manually with a screwdriver until it snaps into the closed position. This will shut off the frunk light and save from running the battery down. Then let the car sit for several hours in a well-ventilated space to evaporate the vapors. When the vapors have subsided pull the hood latch lever to snap the latch into the open position so it can receive the hood upper latch when closing the lid.
If this does not seem to resolve your issue there can be a leak in the filler neck or one of the hoses attached to the gas tank. This is not a common issue however Porsche has published a Technical Service Bulletin TSB9401 (2007) covering replacing the filler neck.
Andy
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