Crank Case Pressure

[CHILAND]

I have the problem of oil leaking between the engine and transmission. My Volvo shop said it could be crank case pressure and to check that first. I have checked for a flame trap clog but there is no flame trap used on this rig.

Is the a way to check for crank case pressure. I know it was possible on my 760.

Thanks,

Clyde

1997 Volvo 850 Sta Wag, non turbo.

[merlin390]

the flame trap is under the trottle body cover on the side of the elbow that goes into the throttle body itself. there should be a pipe and a vacuum line going into the side. give it a twist and it should pop right out. the flame trap is the plastic piece inside.

You will probably need to remove/replace parts of the PCV system: this includes the oil seperator under the intake and the associated lines. Typically if its your first time doing this its a good 6-8 hr job total. there have been many threads with good pics if you use the search function you can find them

-Will

[prasamin]

i have the same problem and will be servicing the PCV system soon....you will need to remove the intake manifold and clean the oil separator and the hoses out of it....I would also try to get to the EGR (if applicable) and clean that out.

[CHILAND]

Thanks for the replies, it looks like I have some work ahead of me.

Clyde

I have the problem of oil leaking between the engine and transmission. My Volvo shop said it could be crank case pressure and to check that first. I have checked for a flame trap clog but there is no flame trap used on this rig.

Is the a way to check for crank case pressure. I know it was possible on my 760.

Thanks,

Clyde

1997 Volvo 850 Sta Wag, non turbo.

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[pfeener]

A quick check to see if the PCV system is working is to remove the oil dipstick while the engine is running and see if it's pushing out smoke. The crankcase should have a slightly negative pressure while the engine is running so no smoke should be pumping out. You can also do the same thing with the oil filler cap. Years ago I had a guage that you could hold over the oil filler hole and it would give you an indication of either negative (good) or positive (bad) crankcase pressure. I don't know if such a guage is still available or not.

Another thing to keep in mind; crankcase pressure is generated in part from blow-by from the piston ring seal. In a normal healthy engine the PCV system is able to overcome this blow-by and maintain a negative crankcase pressure. If the piston rings are really worn and you get a lot of blow-by, the PCV system, even though it may be working OK, will not be enough to overcome the extra blow-by.

[CHILAND]

A quick check to see if the PCV system is working is to remove the oil dipstick while the engine is running and see if it's pushing out smoke. The crankcase should have a slightly negative pressure while the engine is running so no smoke should be pumping out. You can also do the same thing with the oil filler cap. Years ago I had a guage that you could hold over the oil filler hole and it would give you an indication of either negative (good) or positive (bad) crankcase pressure. I don't know if such a guage is still available or not.

Another thing to keep in mind; crankcase pressure is generated in part from blow-by from the piston ring seal. In a normal healthy engine the PCV system is able to overcome this blow-by and maintain a negative crankcase pressure. If the piston rings are really worn and you get a lot of blow-by, the PCV system, even though it may be working OK, will not be enough to overcome the extra blow-by.

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[CHILAND]

Thanks, That is what I am looking for. I will try the dipstick test.

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