Okay, on my 90 740t. The car fails the jiggle test. Pulled the small hose from the "non-flame trap" Y, the brass fitting to the manifold is clear. Replaced the hose, but found out the small nipple on the Y was clogged solid. Opened that up, cleaned it. Also ran a tube down to the hose going into the breather box and blew smoke in. Smoke came out the oil filler so the breather box is clear. Replaced the oil cap gasket, and it still has oil coming out of it and fails the jiggle test. It does however, draw a vacuum when you rev the motor up, but at idle there is definitely positive pressure coming OUT of the fill hole.
Drained the intercooler at the large hex bolt, and got less than a teaspoon of oil out of it.
So now I am stumped. Any thoughts?

I did not solve the oil cap problem until I got a new cap. Bear in mind that it seeped oil with a new gasket even after I put a one way valve (PCV) in that small hose thinking that it was pressurizing the crankcase and causing a main seal leak. Turned out the main seal leak was because of a stupid mechanic (Keith Taylor Motors, Mooresville, NC) who left out the $.25 coil spring in a new oil seal. All cured now - live and learn (hopefully before you have to replace the main seal). Anyhow the new oil cap hasn't leaked for over a year even without the new seal.

Was the new cap a plastic volvo one? I've heard the old metal ones, which I don't think volvo stocks are the ones to get.
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Paul NW Indiana '89 740 Turbo 110,000

It is a black plastic one I got from FCP Groton. I had tried new gaskets and even bending the tabs on the old one trying to get it to tighten up. The new cap fixed it right away and is still tight over a year later.
Jmars 89 745 Turbo 207K

You might try replacing the gasket on the oil fill cap. I noticed that the cam lobe throws oil up to the bottom of the cap and, if the gasket is old, oil leaks out regardless of crankcase pressure.

Hope it helps,

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Will Dallas, www.willdallas.us, www.willdallas.org, 86 245 DL 205K miles, 93 940 250K miles, 88 765 GLE 149K miles, 87 745 , 86 244 DL 200K Miles