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crankcase pressure[740-760/1990] posted by Randy on
Sunday, 3 May 1998, at 12:44 p.m.

1990 740 B230F Auto 160,000

I noticed the smell of oil in my recently acquired 740 and upon raising the hood found the dipstick pushed up about 2" and oil blown around the area. I have just recently checked the flame trap and it was new. I haven't had any problems with the car in the almost 1000 miles I have driven it. The compression is 150, 150, 150 and 140. After discovering the dipstick pushed up I added oil and took it out for a run that included a couple of segments of max throttle and RPM's and when I lifted the hood after returning home the dipstick was pushed up again. What is causing the crankcase pressure to build up like that? I have experienced clogged flame traps before but I'm at a loss at this point. Thanks for any insight.

Re: crankcase pressure[740-760/1990] posted by Randy on
Sunday, 3 May 1998, at 1:46 p.m.

I had a chance to do a little exploring and can add the following to the mix:

When I remove the flame trap and insert a hose into the receiver of the small end of the flame trap holder I find that I have a near perfect seal. I can blow on the length of hose and create pressure that doesn't leak down unless I pull the dipstick or loosen the oil filler cap at which point pressure is immediately lost.
Doing the same "test" on my 88 240 (B230F) allows for a low pressure buildup but it very quickly leaks down.

It would appear that I have a blockage in the 740's plumbing in the assembly that bolts to the block under the intake manifold. I plan to remove that and see what I can find out. Has anyone had this problem?

Re: crankcase pressure[740-760/1990] posted by Alan Carlo on
Sunday, 3 May 1998, at 10:45 p.m.

I read in a recent post that a fellow Volvo enthusiast discovered that the tube that connects to the underside of the oil separator, and extends down into the oil pan, was kinked. He found this out during an engine rebuild. If it is kinked it may be blocked. Do not pull this tube out of the block as the oil pan will have to be removed to reposition it correctly. Maybe you can GENTLY slide a piece of wire down inside it to see if it passes freely. After checking all of the hoses and the intake manifold orifice it may be worth a shot. Good Luck.
Alan Carlo

Re: crankcase pressure[740-760/1990] posted by Jim S. on
Monday, 4 May 1998, at 7:21 a.m.

YES.... that was me, and that would be one thing to check and a good way to check it. having just cleaned the plastic flame trap, I'm not sure the kink could cause the problem now. Because it is open to both passages into the block. Unless the hose and the other port are both kinked/clogged. I would suspect the hose between the manifold and orifice. Was the compression test run cold, and nothing squirted into cylinders?


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