Where is the oil leaking from? Advice please!

C4R 100N · #1 27th December 2019, 06:06 AM

Hi,

My S8 has been leaking oil since before I got it. I didn't think much of it since all of my C4 cars, especially the 2.8l, but also the 2.6l to a lesser degree, give it up like the Exxon Valdez.

After a bit of reading on here though, it seems to me that the V8 engines should be a lot less leaky. Is that so?

I guess I probably would not have noticed the leak so soon if it were not for the conveniently located hole in the noise insulation / under tray. BTW, what is the purpose of that hole?. The oil drips out there when the car is going, and also for a short while after the engine is turned off.

Here is a video of the oil leaking when the engine is going:
VID_20191226_175229816.mp4

Here is a video of the same area a while after the engine has stopped:
VID_20191226_182335624.mp4

Can I ask your opinions as to the most likely source of this oil? The valve cover gasket area seems fairly free of oil and is not wet at all.

Thanks very much for watching!

MikkiJayne · #2 27th December 2019, 08:24 AM

That's the oil filter cover. If its dripping from that, rather than above it, chances are either the o-ring sealing it to the housing is either perished or pinched. Probably someone fitted an aftermarket filter which didn't come with a new o-ring so just re-used the old one. The Mahle filter comes with fittings, as do some other premium brands, but cheap ones tend not to. The number is 077198563. Unlikely you can get that from Audi any more so the Mahle is probably the best alternative.

You're right that that V8 leaks less than the V6, and the 32V V8 is the least leaky of all' The V6 leaks because its breather system is terrible so tends to make a lot of crank case pressure, pushing the oil out of every seal. The 40V V8 has a good breather system but terrible cam cover gasket design so once that fails it also leaks badly. The 32V has the good breather system and much better cam cover gaskets so is the best of the bunch in that regard.

C4R 100N · #3 28th December 2019, 01:47 PM

Quote:

Originally Posted by MikkiJayne

That's the oil filter cover. If its dripping from that, rather than above it, chances are either the o-ring sealing it to the housing is either perished or pinched. Probably someone fitted an aftermarket filter which didn't come with a new o-ring so just re-used the old one. The Mahle filter comes with fittings, as do some other premium brands, but cheap ones tend not to. The number is 077198563. Unlikely you can get that from Audi any more so the Mahle is probably the best alternative.

You're right that that V8 leaks less than the V6, and the 32V V8 is the least leaky of all' The V6 leaks because its breather system is terrible so tends to make a lot of crank case pressure, pushing the oil out of every seal. The 40V V8 has a good breather system but terrible cam cover gasket design so once that fails it also leaks badly. The 32V has the good breather system and much better cam cover gaskets so is the best of the bunch in that regard.

Thank you once again for your time and willingness to share your knowledge. I really do appreciate it. I suppose that it would be useful at this point to inspect the area again with a telescopic inspection mirror to see if I can determine where that oil that is on the oil filter housing emanates from. Hopefully, a pinched o-ring is all that I have to worry about.

Is 10w-40 semi synthetic a good choice were I to service the filter?

Thank you,

Paul

MikkiJayne · #4 28th December 2019, 03:24 PM

Yeah clean with brake or carb cleaner and then have a look with it running to see if you can see the origin. The seam between the housing and the cap is about 30mm up from the bottom - just follow the curve. Worth checking the cap is actually tight too - thats the 13mm M8 bolt in the middle of it. Should be about 20nm.

10w40 is fine for the 32V V8

C4R 100N · #5 30th January 2020, 10:40 AM

Quote:

Originally Posted by MikkiJayne

Yeah clean with brake or carb cleaner and then have a look with it running to see if you can see the origin. The seam between the housing and the cap is about 30mm up from the bottom - just follow the curve. Worth checking the cap is actually tight too - thats the 13mm M8 bolt in the middle of it. Should be about 20nm.

10w40 is fine for the 32V V8

OK....I have decided, after doing as you have suggested, that the oil is perhaps coming from the oil pressure switch that screws(?) into the oil filter housing.

I used a telescopic inspection mirror and could see that there was oil running along the length of the switch. Can i obtain better visibility of this through removing the air filter box/housing, as I have seen reference to on the internet?

Would removing the housing afford me the easiest way to replace the switch if necessary? Does anyone have any suggestions on how I may best proceed?

Thanks as always,

Paul

MikkiJayne · #6 30th January 2020, 04:49 PM

Yes removing the air filter box is pretty straightforward, and will afford better access to the oil pressure switch. From memory the 32V has the early type with the single spade connector - those were prone to leaking so not surprising its coming from there. I don't recall the exact layout of the 32V tbh so can't comment much on what contortions or special tools you need to get the switch out. Its non-trivial on the 40V!