White smoke equals steam. If there is no coolant leaking, try parking on a very steep hill or ramp, then get the rpm up to 5500 in neutral several times. Check the pavement for water. You could possibly have a muffler full of water.

Klaus
--
98 V70Rawd(108Kmi), 95 854T(88K mi), 75 164E(173K mi)

I think what your mechanic says makes sense if it is really oil. In all of the cases (clogged rebreathing vent, turbo or leaking valve guides) the oil consumption would be high, possibly more than 1 quart per 1000 miles. Is it?

Is it possible you are seeing condensing water vapor? Does it smell like oil, not smell at all or smell like coolant? If it is water then you might reasonably not see it till the engine is warm enough to vaporize the water. You might see it only at idle because at faster revs the flow thru the exhaust system would be too fast for the vapor to condense near the end of the tail pipe. With oil I would expect you to see more smoke at higher revs.

If it is water it could be any of leaking or cracked head, water pump, or turbo. It seems to me that any leak between oil and water would result in a little film of oil floating on the coolant - you would see this by looking in the reservoir or radiator after letting the car sit overnight, when the engine is stone-cold and has not been run. That would confirm whether water/coolant is mixing with oil somewhere.

If so, maybe a pressure test of the cooling system would help - sooner or later some amount of coolant should move through the leak and you might be able to find it, in turbo oil lines, on plugs, or whereever.

Black = running too rich
White = Possible coolant getting into chambers some how.

First, there is no such thing as white oil smoke. The smoke is either blue, black or white. In general blue means engine running too rich, black means engine burning oil, and white means coolant leak.

It is possible that you may have a hairline fracture or pinhole leak somewhere in the block. This happened to me on one of my cars and not until I popped the hood and looked at the water pump did I notice only very slightly a pinhole leak with steam coming out. It was enough to drain not only my radiator, but peg my temp guage. Nothing ever showed up on the ground.