Positive Crankcase Ventilation (PCV) is an important feature of all car engines. Volvo has an unusual (but not unique) PCV system which involves an oil separator under the intake manifold (for all models) and a flame trap near the throttle body (for normally aspirated = non-turbo models like this).
Volvo PCV systems have a tendency to clog up easily if oil is not changed regularly. One sign of this is smoke coming from the dipstick and oil leaks at the fill cap, camshaft seals, or (worst of all) main seal at the crankshaft output.
This car has light smoke but no measurable pressure at the dipstick so it seems as though the oil separator and hoses aren’t too clogged up. But the flame trap is always suspect so removed the flame trap screen and found it fairly clogged with globs of oil and bits of solid crud:
Disassembled and cleaned all the separate parts of the flame trap assembly well using throttle cleaner, toothbrushes and toothpicks.
Sealing o-ring was OK so didn’t need to be replaced. Seafoam treatment may also help clear out the entire PCV system a bit.
Many experienced owners say to just remove the flame trap screen since Volvo reportedly stopped including it in 1998. But I’m content to just clean the flame trap and re-install it. Needs to be cleaned about once per year and is not hard to do.
One other issue with the flame trap on this car is that the original hose to the intake manifold vacuum tree was gone and had been replaced with an oversized soft rubber tube which had holes worn in it and did not fit tightly at either end.
Replaced this vacuum line with proper Volvo parts.
1997 Volvo 850 Wagon Project 