sportsphotog

I have a 51k mile 2003 996 with the X51 kit on it. I am experiencing very significant oil loss. I say loss because I see nothing actually burning out of the exhaust pipes, as I have with others cars I have owned in my life. I have absolutely no oil leaks and a spotless engine and garage floor. I am losing about 3 quarts per 5k miles (basing this on how much I have to add on occasion). My oil comes out clean during the oil change, as it should since it is mostly new. I catch a whiff of oil after I get out of the car but still not a single sign of it anywhere EXCEPT for on the left (drivers side) tailpipe. The tailpipe is discolored a bit with soot but I can't seem to see any smoke or oil anywhere. The soot wipes off fairly easily. Oil pressure generally runs close to 5 for a 4th gear 60mph run. There are no codes, lights, anything other than my oil level showing me the loss. Anyone have any clues?

Imo000

Any sign of oil in the coolant?

fpb111

Search "Failed AOS"

Here is one of 71 that came up.
https://rennlist.com/forums/996-foru...aos-issue.html

Byprodriver

1st step is to verify the actual oil level with the dipstick.

jumper5836

pull the spark plugs and have someone who knows how to check the cylinder walls for scrapping/scuffing. Probably only need to do a check on bank 2 cylinders.

I have no signs of oil burning but I need to add oil every time a visit the gas station. I have one scored cylinder. But you may be lucky and have a bad AOS though usually there are signs of smoking from both sides and not just from one exhaust side. Other signs of something wrong are that cats are burnt out frequently.

Pac996

Not a porsche camaro from years past but an overhead cam engine than would leak at the bearing only when the engine was running since that is when it got pressure to put oil out the seal at the end of the shaft which happened to be a good spot to drop oil while running so that the engine or parking area wouldn't get drips. But every week it lost a quart at least driving just 100 miles. Might check your seals at the ends of the cams or such. I wont say check the radiator overflow resevoir......been there and paid more than I paid for the car. If there is oil in your radiator water.......good luck.

Macster

Assuming the oil loss is real, that is your numbers are real, the engine is using one quart every 1667 miles which while high is not too high.

IIRC Porsche guideline can have the oil consumption up to 1 quart every 600 miles.

If the engine is not exhibiting any untoward behavior, is not making any scary noises, smoking upon startup (except the normal once in a while), not smoking any other time.

Let me take a side trip here: With the engine fully warmed up hard accelerate the car up to speed in say 3rd gear to around 4K rpms, then let off the throttle and let the car slow down on engine compression until the rpms drop to around 2K then floor the throttle again. Whenever you can check the rear view mirror for any signs of smoke during the acceleration phase, then when you let off the throttle and then again when you get back hard on the throttle. Do this test in the AM or PM driving away from the low sun to have the sun at your back to make the smoke more visible.

If the engine doesn't smoke in the above test and there are no other signs of trouble then your engine is ok it just consumes more oil than some other engines, but not as much as other engines.

Now, I have a theory that some engines that use oil at a higher rate than average are really being unfairly labeled as 'oil burners' because the AOS is not working very well and allowing an exceptional amount of oil vapor to pass through into the engine (intake manifold) where it is burned and this accounts for the high oil consumption.

Just a theory of mine.

Would I replace the AOS with no other signs it needs it?

It would depend upon the severity of the oil usage and the cost of the job. and the miles on the AOS. Also, I'd run this "theory" by a senior Porsche techor two and get their input. They may dismiss it and that's that.