Hi Klaus,

I'd guess a PCV at the sieve or flame trap valve. Had you tried removing the PCV vacuum hose at the air intake port, or throttle body? You may have at least two vacuum hoses at the PCV flame trap / valve / sieve. I forget your era 850-series PCV and vacuum hose routing.

With a paper towel around the end of the hose, to spare you the nasty oil flavor, blow through the hose with the filler cap off.

You may want to futz with the PCV complete. That crazy oil breather / separator box and clog over time with condensating hydrocarbons from combustion by-product and vapors that come out of the hot oil, like water. Oil that is not changed often, or suffers from short trips that does not allow you the long motoring runs to dry out, if you will, the engine oil, further enhances the clogging action of condensating hydrocarbons.

Check all connection vaccum or air intake system connection. Some of them vacuum lines may brittle, split, or in otherwise not good condition, and may not seal well.

The cams are coated in carbonized oil. The prior owners used dino oil and did not change it regularly?

As this is a turbo engine, creating more forceful combustion blow by, with a clogged PCV, it is very possible to displace the engine oil seals.

In such condition, you may want to inspect the throttle body and air intake port (manifold), for heavy carbonization and other hydrocarbon gunk. The vacuum ports in the air intake assembly including the throttle body and air intake port (manifold) can be clogged, preventing proper action through running engine air intake vacuum.

Also, a compression test or leak down test helps.

If you can ensure a freely breathing PCV, that is sealed against vacuum and air intake leaks, that can, in some instances, relieve oil sump chamber pressure that can force oil to seep past the engine oil seals; certainly the lower engine seals.

You may want for an oil change, using perhaps a quality dino oil, with some detergent action in it. Or, use a very high quality filter, and go for Mobile 1, or some of the private-label brands with a quality synthetic to melt or clean away carbonization in the engine oil sump chambers.

Check the OBD codes, yet? There may be fault codes set related to the prior owner neglect.

I hope this help and your 1995 Volvo 850 Turbo wagon delivers reliable performance as you like for cost-effective ownership.

Questions?

Thank you.

Normally Rear-Wheel-Drive Volvo MacDuffed on a Sundae.
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