My car has these problems: broken speedometer, replaced motor mounts, windshield wiper that doesn't hit the window, light out on the dashboard, etc. But my question isn’t about those (just listing for your info). For a while, my car has been leaking oil (no burning). I was told that it’s a valve cover gasket. But I looked and the oil is coming out from underneath the oil filler cap on top of the engine. Almost like a blowback.
When I stop to fill up the gas tank and check the oil, if I have been driving for a while, there is pressure build up and blows a little oil out of the dip stick tube. The other day while it was running, when I opened the oil cap, it hissed with pressure like a radiator cap. There’s supposed to be oil pressure, but I’m wondering if this is normal. In your professional experience, is something blocked or clogged that causes a build up of pressure that spews oil out of the filler cap? Thank you.
If you had excessive blowby from worn rings and all, then you would have excessive smoking and oil consumption through the engine. It almost sounds like your PCV (positive crankcase ventilation) system is not feeding blowby gasses back to the intake so crankcase pressure is building up in the engine.
The Volvo 850 has a breather box located under the intake manifold. Make sure the vacuum lines to the box are not deteriorated or damaged, and if the box has never been replaced, then it might be a good idea to do so. Failure of the crankcase ventilation system can cause gaskets and seals to fail which can be very costly to repair if the system is not corrected immediately. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will be able to give your car a comprehensive inspection and address all the issues that you've listed.
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