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.

Crankcase pressure is sucked out due to being connected to the inlet system.

Put too much oil in and there's less room for the air to move around hence the pressure build up.

To give you an idea of how much pressure there is, we use vacuum pumps on race engines which gains more hp.

MG

I am going to check the PCV valve at the weekend, could you confirm that what I am looking for is the black circular valve on top and towards the back of the engine.

When you explain it like that it kind of makes sense. The pressure in crankcase is not constant but pulsing as pistons go up and down. If there is less room it cannot swallow pulses that good and peak pressure at the top of pulse is higher and lower at the bottom of pulse making greater difference in max and min pressure. I can see how this could effect seals. This would also have more effect with low number of cylinders and less with higher number of cylinders I guess.

I checked the oil level in mine today,and after 500 miles it seems the same so maybe the leak is not as bad as first feared.

I have had a quote of £300 +VAT all in to change the crankshaft seal, plus a little extra should the cambelt itself need to be replaced (Was changed 3K miles ago by same garage). I dont know how this compares to others.

If your crankshaft front seal is leaking, your timing belt will be saturated in oil. So if your timing belt was replaced even 300 miles ago, I'd still be replacing it.

It needs to come off anyway to replace the front seal, the extra cost will be the belt itself, not labor. I personally wouldn't be happy running an oily belt. If it busts teeth, the cost of salvation could be crippling, probably spell the end of your car, depending on what engine speed the belt failed at.

Good luck!

Still monitoring oil use, done 700 miles now and the dipstick has dropped something like 1/4 of a litre in that time.

I have checked and cleaned the PCV valve, there was a lot of carbon inside but it seemed to be working correctly.

I have also cleaned some of the oil off the engine undertray and from the bottom of the sump. I have no ramps, so removed the lower fog grills and reached in through there. Luckily my arms are quiet skinny so I could remove quiet a lot.

A decision will be taken on what to do with the car when we get back from our family holiday to the south of spain, and yes I am using the A8 to get to Estepona via Santander, finger crossed it will manage the 2.5K miles or so it will be doing during 3 weeks from mid June.

I now have an idea of how much oil its loosing and its not a lot really. The 8 has recently completed a trip to the Costa Del Sol and back, 2200 miles were covered in total. Today I checked over the car, and needed to add 1/2 litre of oil and a tiny quantity of coolant to the engine.