Let's face it any Porsche 911 will leak a little oil at some time during its life. A small oil leak is of little concern. However, if you suddenly experience what appears to be a good size oil leak some days, weeks, or a couple months after an oil change and before jumping in with more invasive and expensive fixes here are the common causes in order of how common they are:
- The number one reason by far! The technician, when pouring the oil into the filler neck, poured too quickly and spilled some backflow oil from the filler neck that ran down onto the engine sheet metal. Even if one uses a spray degreaser to clean up the spilled overflow some oil will continue leaking down onto the right side valve covers, the exhaust pipes, and the floor for quite a while appearing as a large leak and a smelly burned oil odor.
Many times this is misdiagnosed later on as a leaking valve cover where no leak exists. It may also explain why leaking valve covers seem to mostly be diagnosed on the right side bottom cover of the engine just below the oil tank filler neck, go figure? - Removing the smaller oil filter from the side of the engine as part of an oil change is inherently messy splashing oil on the engine case and suspension components below it. If the technician didn't clean up the splashed oil as part of the servicing it can subsequently appear to be an oil leak.
- If the oil return tube on the right side of the engine case was detached to drain the line and was not properly reseated and now leaks down the right side of the engine case.
Due to the metal tube's propensity to leak after reinstalling it many folks including me do not remove the tube even though it is described in the factory literature as part of an oil change. The amount of oil in the line is small and is not really relevant when the system at refill takes just short of 10 quarts and the entire system holds about 12. - The oil filters' seals' were not lubricated when installed or the oil filters were not properly snugged down when screwed on resulting in a small to a large leak. Step #7 in the step-by-step oil change section in this document describes how to properly snug down an oil filter when changing the oil
- The technician squeezed the new filter a little too hard when tightening it up with a filter wrench or applied the wrench too close to the base of the filter housing breaking the crimp seal at the base of the filter resulting in what can be a large leak. Also, some time ago I read about a defective run of oil filters for our cars where the crimped filter cartridge housing closure fails and a lot of oil leaks out. I have not heard of this recently but it is worth mentioning.
- Another less common source of a leak is the flex pipe that leads from the filler neck to the oil tank. Conceivably it was dislodged, torn, or punctured by the funnel tip when the oil was being filled. This also can appear as a good size oil leak to the far right of the engine compartment.
- Brett Stevenson from the Rennlist group on Facebook notes an additional cause: "When I drained the oil reservoir some oil made it into my side skirt and leaked out for days near where the [ oil tank] drain plug is." If you see oil film or wetness under the car just forward of the right rear wheel well this may be the source
- Other potential causes of oil leaks or consumption are discussed on this page.
For all of the above issues, consider going to an auto parts store/Walmart/Amazon and buy three cans of spray CRC QD or some other brand of electronic cleaner and hose off the bottom of the engine as well as any oil-wet areas nearby on the engine tin and valve covers. I use this stuff all the time because it degreases well and doesn't attack plastic or rubber. After a good spray-down, the engine will be bone dry and the source of the leak can subsequently be better identified.
When contemplating the above procedure do not use CRC or another brand of "Electric Motor Cleaner" or Carb & Choke Cleaner as they are different from the "CRC Brand QD Electronic Cleaner" in that their cleaning solvents melts plastic parts such as electrical connectors. Whatever brand of electronic cleaner used read the lable carfully to ensure it is apropriate for use on non-metallic parts.
Avoiding unnecessary expenses:
Once the source of a large leak is found don't fall into the expensive trap that all the leaks on the engine need to be addressed. Only the one leak that is large enough that it drips should be of concern as small surface oozing of oil seals that simply attract dust and grime are common, somewhat inherent in the design of the engine, and need not be addressed.
Be wary of common upselling of services such as replacing all the valve cover seals when only one is leaking. The primary cause of a valve cover leak has to do with how the previous seal was installed, for example when the hydraulic valve lifters were replaced, so disturbing a seal that is not leaking may set the stage for ongoing seal replacements.
Other potential causes of oil leaks or consumption are discussed on this page.
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. Filling should be up to 1/4 to 1/3 of the way from the bottom of the dipstick's measuring range with the engine fully warmed, running, and on level ground. The measured volume will expand when the engine is very hot as can be seen on the oil gauge on the dash.
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