I have recently been through all sorts of crankcase vent issues with my 1994 850 and can, I hope, provide some useful advice.

The oil rings on these cars appear to wear faster than the compression rings. This leads to some oil use later in life but should not lead to serious problems. As the get oil vapor in the crankcase it comes through the crankcase vent system and flame trap, mixed with the induction air and burned. This oil vapor attacks the plastics and rubber used for all of the components of the crankcase vent, including the 'fresh air' inlet where the air from the air box and the crankcase vapors are mixed. This is why your flame trap has a hole in it.

The holes in the flame trap and the size of the aperture in the flame trap fitting in the 'fresh air' inlet play an important part in regulating crankcase vapor pressure. I recently replaced the 'fresh air' inlet (about $50) and have seen a noticable decrease in oil consumption.

First off, check/change your oil and filter. Check coolant. Change plugs. Check rotor and distributor cap. The engine control system controls timing, so if the timing is bad you probably have a bad cam position sensor. Check/change the air filter. Check the air mass meter for correct function. Check all vacuum lines -- these are famous for failing in hidden places. Check electrical connections to all engine sensors. The sensors typically don't fail, but the connectors and wires do. Check compression, including a leak-down test.

Try an experiment: wrap lots of electrical tape around flame trap to seal hole. This is temporary to see whether it solves the smoke problem.

Probably the best thing is to take your car to a good independent Volvo shop and have them diagnose it. IMHO, an independent shop is more likely to give you sensible, affordable advice.

Good luck.
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-- Bruce / '82 244 (315k miles!), '86 745, '87 760Ti, '94 854

White/blue smoke is a fatal indication usually due to lackness of lubrication. It is produced by dry friction between metal parts.

Be sure flame trap has nothing to do with it.

Oil burning produces dark smoke.

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850 GLT Aut.