Pretty much says it. What happens is when under neutral load (not engine braking or accelerating) for more than 30 seconds, oil seems to be building up under the valve cover and getting pushed out the vent tube and into the intake air duct. It will block out the sun when this happens, and it seems that some oil is making its way all the way through the engine (turbo downpipe has oil in it). If I run it hard and floor it up hills and otherwise work the engine, there is no problem, and its a pleasure to drive, but under light load, all hell breaks loose. The smoke is accompanied by a surge that I can control by downshifting and letting the engine burn the oil out. Quite scary.

The engine is a 4D55T with a 4D56 head, it has a rebuild that is less that 15000ks old and recently blew a head gasket (hence the new head). After putting it back together, this started happening.

I was able to observe the phenomena when idleing the engine after a cold start. For some reason, it will only puke oil on a cold start, and can idle for an hour without incident once hot.

Otherwise the engine runs very well and has good power and oil pressure.

If you have any ideas, please share them, because as of right now the truck is not safe to drive.

Well, I can definitely confirm that too much oil is getting on top of the head. Started it up this morning and poped the fill cap off to see what is happening. Slowly but surely, valve cover will fill with oil until it reaches the vent tube and gets ingested by the engine.

Oil pressure seems to be a bit on the high side, but I have no idea what is normal for this engine.

What is the normal oil pressure reading for idle and for load on this engine? When its cold it sees 90 psi easily and any extra throttle will peg the gauge at 100 psi. when idling hot, it is closer to 30psi, and can still go close to 70 when reved up.

those oil pressure numbers seem about right. that is a very strange problem. I will ask my buddy who is a VW Diesel freak, he might know of a solution.

If you just had the head off and changed the gasket, what are the possibilities that you have an oil passage partly plugged?

Good call. RTV used on the gasket?

What bae146 said.

I carefully compared the new gasket to the old one, and all the holes and passages were the same. Only difference I could find was a better rubber seal around some of the water passages. No RTV sealer (or any other sealer) used anywhere on the head gasket.

The oil drain galleries are slanted in the head, do they continue in that direction in the block? or are they vertical in the block? I heard of a similar case happening with an older VW diesel, but never found out what the cause was.

Any chance there's too much oil in the engine?

All I have to go by is the dipstick tube, because I don't know the capacity of the engine. My guess is that its 6.5L (15w40) in there, maybe a bit more. Its right in the mid range of the dipstick when the engine is warm. When I get the chance, I will pop the valve cover off again and see if there is a plug in the drain gallerys, might also try draining 0.5L of oil out of the sump and see what happens.

The problem is obviously a restriction preventing the oil to drain back into the sump.

The Heath Robinson solution would be to fit an overflow pipe from the tappet cover to the sump (join up with the turbo's oil return pipe).