Quote:
Originally Posted by Image
Indeed .... that's one scenario I'm prefering not to think about 
Gradually working through the possibles with the cheap and accessible ones first ... but eventually I'll have to bite the bullet, remove a load of plastic and delve down the back of the engine .... what is strange is that it smokes when cold and once warm neither hard acceleration nor hard engine braking effects the smoke .... wouldn't those more expert than me expect the manifold vacuum to draw more oil past the seals into the intake side on over-run and hence give more smoke if the seals were gone??
K |
I think you are thinking of the phenomena of worn valve guide seals where an engine would smoke a lot after being stood a while and started, due to the oil seeping down the stems, finding it's way into the combustion chamber and the back of the exhaust valves where it got burnt and cleared after a short while, with very little smoke thereafter even under hard acceleration.
However, with foot off the pedal and say cruising down hill on overrun a brief puff of blue smoke was seen as the accelerator was depressed this confirmed in most cases worn guides.
This is due to an engine which incorporates a throttle valve/plate in the inlet system, (not to be confused with a throttle body) which when closed on overrun it creates a high vacuum, (not the correct term but one every one understands ) in the inlet tract drawing oil down past the stem seals.
However, throttle plates are mainly on petrol engines, with very few being used on diesel engines, the 75 engine doesn't have one and other than excess engine crank case blow by, inefficient PCV or oil mist from the turbo, there are no other places that oil can be introduced into the inlet tract.
There is also one fault that can give the same problem of smoke at all times which is worn piston rings and bores especially oil control rings which can sometimes suffering from varnishing and gumming preventing efficient bore wiping.
The first thing you need to do is identify if the smoke is from oil or derv sometimes your nose is the best test.
Smoke from derv can be blackish or white, black resulting from insufficient air or excess fuel for various reasons, white being unburnt fuel again due to various reasons.
Blue is oil.
Occasionally due to oil dilution by derv which ' thins' out the oil, this ' thinner oil ' can pass the rings.
Has the problem been building up or has it suddenly happened ?
Is there copious oil in the intercooler pipe work, there is always a bit.
Non of the above points to the actual problem or cure but may help you to look at different areas.