Audi A8 - Oil leak - front Passenger front (UK) side of engine
 

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My A8 3.7 QS has sprung an oil leak at the front of the engine, its lost about 1/2 litre of oil in 400 miles so far.

The engine under tray is soaked in oil, and the front of the engine has oil all over it.

Urgent thoughts.

Oil cooler?

oil cooler was replaced by Amersham Audi in 2008, its not done that many miles since. The bulk of the oil appears to be on the UK passenger side of the engine which I believe is the opposite side to the cooler.

I am attaching some pictures.

See hi res pictures below

i think whipping off the undertray and looking up at the source will likely show a lot more... Those photos look fairly clean and dry - apart from the pooling on the tray so cant really provide any good guesses....

Maybe something daft like a loose oil sump plug or oil level sensor..... ?

The photos dont really show how bad it is unfortunately, the undertray is completely soaked in oil, it was bone dry 2 weeks ago. The same with the lower part of the engine. On the second picture just below the belt pulley is the silver coloured pulley, just behind and to the right there is oil all over the block at this point which again was not there 2 weeks ago, and if you look down from a different angle you can see a pool of oil sitting on top of the engine block.

I am driving it 120 miles tomorrow, 120 miles on Tuesday and 150 miles on Wednesday so I'll certainly have a rough idea of how much is currently leaking out.

I fear it might be the crankshaft oil seal, which due to the effort to remove the front of the car and cambelt to fix it, could mean I end up selling the car on. With a 2500 mile run to the Costa Del Sol and back coming up in 3 weeks I need something that I can reasonably trust, unlike the A8 at this point.

I had an ex Audi mechanic look at the car this evening, he removed the upper cambelt covers and peered down towards the crankshaft his verdict is that it is indeed the crankshaft seal that has failed. Due to the cars mileage, he has suggested not replacing it as the replacement may also leak due to the wear on the Crankshaft although I dont know if this would be the case.. So at the weekend I'll clean as much of the oil off as I can to enable me to monitor how the leak develops.

For now the car is still on for the Costa Del Sol run, assuming oil loss remains consistent and predictable. I have 2 weeks to decide, but do have an alternative albeit much smaller car available if needed.

Just out of interest, how high is the oil level?

Having too much oil creates excessive crankcase pressure and the first sign of this is an oil leak... The pressure has to go somewhere!

When replacing seals like this, it's usually possible to fit the seal slightly further in or out so to use a different surface on the crank and so avoiding and ridges in the crank.

MG

oil leak
 

If the crank seal leak is due oil pressure build up...it might be worth checking the pcv valve as it meant to control the oil pressure in the crankcase.

I have heard this many times but it does not make sense to me. Crankcase is freely vented at the top to the intake so any pressure will escape to intake unless there is a blockage. And if there is blockage cylinder blow-by gasses will build up pressure in crankcase and could blow seals irrelevant from oil level.