oil consumption and pressure - www.AudiV8.com - Audi V8 Forum / Audi A8 Forum

As some may be aware, my car is currently running a 4.2 ABH engine in my 1990 (PT) car. I have been keeping an eye on oil consumption for a while, as the engine is a bit of an unknown quantity, and has a tendency to blow some oil smoke on hard acceleration, especially when doing a lot of acceleration/deceleration.

The engine is running the original electronics and injectors for the PT engine, with an 'ABT' derived eprom in the ECU. De-cat'ed. The exhaust is a hybrid of PT manifolds, x-pipe, cat pipes (minus Cat honeycombs), and the rear exhaust from the ABH setup.
the odometer on the donor car indicates 145k miles, but I suspect it is more likely 200k mile plus.
Emissions at the last MOT were well within parameters. There being negligible difference between values with Cats and 3.6L engine, and without Cats on 4.2L engine.
Oil pressure is consistent at about about 1.8Bar idle in park or neutral, and 4.5Bar on load.

In general, oil consumption has been in the region of that quoted by many sources, 1-2 litres per 1000miles. I've mostly been doing motorway miles, at about 70mph. Fuel consumption has remained fairly consistent at about 25-26mpg, 17-18L/100miles. It increases markedly when doing lots of town driving. I have also noticed there is a greater tendency to smoke after an abrupt right hand bend, followed by acceleration. ie. UK roundabouts.

When I installed the engine, a compression check showed comparable values across the 8 cylinders. I shall of course do another, and record the values this time.

My initial thoughts were that the valve guides and stem seals are in need of replacement. (I once before had issues on a WR engined quattro, where the seals were breaking up, resulting in part of a seal remaining on the guide, and part of it travelling with the valve- that then encourages oil to be squeezed down the guide.) they probably are in need of attention.
I removed the throttle assembly recently, to clean and inspect. I found that there was a small amount of oil pooled in both the upper and lower chambers of the intake assembly.

In the last week, I have watched oil consumption apparently increase, but not consistently. In some cases, it appears to be not using any oil at all, other times it appears to be using more.
I top up the oil whenever it approaches the minimum mark. I also top up to just below max if I am going to be driving in excess of 200miles. I routinely check oil at rest stops.
On todays drive, after about 2 hours continuous driving at about 70mph, I noticed that oil pressure had increased, and was remaining high. Off scale, even.

So. my points to raise discussion and gain some feedback.

I have a suspicion that oil is being pushed through the breather system.
I know there is a small weep of oil from the rear of the left head gasket. Evidenced by oil tracking down the crank position sensor and lambda cables.
Sometimes, I get a smell of burning oil when driving, with no evidence of oil being blown through the exhaust. I expect this is due to accumulated oil dripping on the lower end of the manifolds/cross pipe.
There is plenty of evidence of oil being retained in the left hand cylinder head.
Sometimes, the oil level appears completely unchanged after several hours of driving, even though there is plenty of evidence that it should have burned some oil.

questions and hypotheses. Is it possible that oil is being trapped in the cylinder head? The cause of this might well be down to one or more blockage in the drainage/passages back to the sump. What about the oil retention valves? Can these/have these any history of problems causing oil to accumulate in the cylinder head, or in the breather system?

85 WR quattro
90 V8 Silver, 91 V8 Black, 93 V8 Lago
93 100e quattro V6. Titan, i think

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