Oil on plugs


I have a 2012 Audi A6 with a 3.0T engine.

I recently did the PCV, waterpump and thermostat. Since doing it, my car has been playing up. At first, the No 3 cylinder began misifiring, I found the plug was oily and replaced it. Went a few hundred miles, it happened again with the same cylinder, this time, 2000 miles. happened again, changed the spark plug, drove a few hundred more and of course, I am here for a reason… It happened again, but with a twist! No 1 this time. They started to both do it, nowadays though, it is No 1. I tried a new PCV, did not help at all. I have no idea what is going on with my car, but it doesn’t seem like a classic problem at all!

Yes, it does seem like a classic problem… Poor crankcase ventilation OR worn piston rings letting oil past into the combustion chambers. How many miles or kms on this engine?

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The valve cover gasket is probably leaking oil into the spark plug wells and filling them with oil.


Replacing the valve cover gasket will fix the problem.



I wish that were it! My wells are very dry… No signs of oil unfortunately!

Poor ventilation? What could this be caused by? Two piston rings going together like this, surely that is a bit bonkers? The odds have to be crazy low! Car has 160,000kms. Compression was good on all the cylinders…

If pressure builds up in your crankcase it can push oil past the piston rings and foul the spark plugs. If the new pcv valve was bad or installed incorrectly, that could happen. Or if tnere is a clog somewhere else in the crankcase evaporation system that can happen. The crankcase pressure can be checked with the proper tools.

2 piston ring sets failing together isn’t bonkers at all. They both have the same wear don’t they? Why wouldn’t you expect them to fail at the same time? The successful compression test tells me it is not the rings.

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In addition to replacing the PCV valve itself, the OP should either flush the PCV hose with an appropriate solvent or simply replace the hose.

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If the 3.0T engine designation means you have the 3.0 V6 turbocharged engine, there may be a check valve in the evap system that has failed. I had this problem in a Saab turbo. Instead of fouling plugs, it blew oil out the front crank seal.

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Fair enough it isn’t bonkers to fail at the same times, though they are not notorious for going to early and to happen to go just after I worked on it, that is just a massive coincidence.

Bit of an update… So I put a scope down the cylinder and this is what I found.
Google Photos

It is coming from the exhaust side only. The rest of the cylinder is dry. This was after turning the engine over a couple of times. I am supposing this only points to a head gasket, but that would just make it weirder, as there is no connection that I can think of, between the head gasket going and the work I did to the car. To top it off, these cars very rarely blow the head gasket.

Because gravity takes it there. It is not coming from the exhaust side, it is ending up there because on a Vee shaped engine, the exhaust it the low side.

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That makes sense. So would it be coming from a blown head gasket? Are there any other possibilities?

Not a head gasket…to repeat myself, excess crankcase pressure, maybe from a failed check valve. Test for excess crankcase pressure.

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So it was really note-worthy, that I noted the vacuum when pulling my oil cap previous to working on my car. After changing the PCV, I noted it was the same, quite high, took some strength to get off. Now almost all the vacuum is gone. So that begs the question… What would cause a loss of vacuum that would also cause oil in the cylinder?

Go back and re-read my posts

You say the compression is good. I ask what are the numbers which led to that comment?

Excellent would be 195ish or so.

Something to keep in mind. It is entirely possible to have great compression (195-200) and still have an oil burner which is caused by a ring problem. The compression rings may be fine; the oil control rings not so much.
Like most things, there is a gray area there.

I don’t exactly recall, though I compared them with what is considered normal for my car and they exceeded these numbers. Also noteworthy, the left and right bank both matched, the cylinder with the oil on the plug was no different.

Considering I drove this car for 60,000km without an issue, then barely a 100km post PCV, water pump and thermostat replacement, this issue came, the massive odds are that it is somehow related. I will pull the head off and inspect the piston if I have to, though it is highly improbable…It would defy reidiculous odds.

what is your oil change interval, in both time and mileage terms?
are you using the “euro-spec” oil?

I change every 6 months, every 15,000km, I use the recommended spec in full-synth.

your problem sounded like oil control rings “stuck” from the oil coking, so I asked for the OCI

your numbers seems to be in line with recommendations, although many people questioned overly long oil change intervals recommended for modern European cars

So you are suggesting that oil caked 100km after the major works I did, completely unrelated?