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Crankcase ventilation problems[700/1988] posted by Gary DiFrancesco on
Monday, 26 October 1998, at 10:24 a.m.
This is a posting to go along with Monte's concerning crankcase ventilation. This past weekend I finally got around to cleaning the throttle body on my '88 740T that has been idling unsteadily. The throttle body was gross which is not surprising since I doubt the P.O. ever had it serviced. A good cleaning, new gaskets, and new o-ring, and the engine idles like a dream. Never thought I'd see this engine idle this smooth.
While the throttle body was off, I attacked the crankcase ventilation system. I have been experiencing a bad oil leak from the o-ring at the bottom of the turbo oil return pipe. Oil consumption has been 300 - 450 miles per quart. I don't think the engine is burning oil since there is no smoke, the new exhaust system (last spring) is not overly carboned up, the spark plugs when replaced last summer showed no sign of fouling (just the typical yellowish deposits), and minimal oil coating in the intercooler and associated plumbing. Besides, I can see the oil dripping from the block near the turbo oil return pipe with the engine running. In addition, I performed the "oil cap jiggle test" a few weeks ago and there was a definite jiggle. Going after the "flame trap" and breather box is much easier with the throttle body off.
I did not find any of the passages or hoses in the vent system plugged. I cleaned out all the passages anyway on the throttle body, intake manifold, and flame trap housing. I removed the breather box only to find out it is a sealed unit. I was able to blow air through all the ports, so I concluded that it was not plugged. When reassembling the vent system and throttle body, I replaced most of the vac. hoses since they were old, hard, and/or disintergrating.
The oil filler cap still jiggles at idle. Though when I go to lift the cap off, I feel a slight suction which I can't remember existed before. Apparently there is still a pressure pulse in the crankcase that is causing the cap to jiggle. Time will tell whether or not the crankcase ventilation is improved. Reduced oil leakage will probably be the best indictor.
My questions to the gurus out there are:
1. How much suction should I expect with the vent system working properly? Should the oil cap suck down hard, or is a slight jiggle with what appears as an overall suction enough?
2. Did I miss anything when servicing the throttle body and vent system? Anything else cause a crankcase vent problem that I missed? I thought of bad rings as a possibility, but wouldn't see more evidence of burning oil?
Thanks,
Gary DiFrancesco
Re: Crankcase ventilation problems[700/1988] posted by Mike Harrell on
Monday, 26 October 1998, at 6:59 p.m.
I just purchased a 87 745 turbo that was blowing oil from the oil fill cap on the valve cover. I took a rather heavy handed approach. I bought a can of Gunk motor flush. I warmed the motor, turned the motor off and then poured the motor flush down the large hose leading to the flame trap. Initially, the motor flush would not move through the flame trap. Within a few min. it was running through the hose and into the flame trap as fast as I could pour it. I then blew through the hose with compressed air, started the motor and let it idle a few min. Then drained the oil and changed the oil filter. Just to make shure all of the motor flush was out, I again blew through the flame trap with compressed air. I plan to drive the car about 1,000 miles and replace the oil and filter again. I know this is probably sacrelidge to some but I think this is the fix. The motor is no longer blowing oil out the breather.
--Mike/Alexandria, Va
Re: Crankcase ventilation problems[700/1988] posted by Len Kelly on
Monday, 26 October 1998, at 10:00 p.m.
Dear Gary,
My only experience is with 240's and on the 88 and later models there is no suck down as on earlier models. The flame trap is higher than the intake manifold and is inverted, and this says, the Volvo Problem Solver, is the reason for no suck down on non turbo 240's. There is no mention of the 700 series in this reguard but I understand they are similiar. May be worth looking into.
Len
--VCOA#8933