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Testing for vacuum V70-XC70

posted by  KlausC on  Sun Jun 24 18:22 CST 2012
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last visit: Fri Oct 24 10:15 CST 2014
[RELATED]

Darn, hit return rather than tab...

There should be a small amount of negative pressure at the oil fill cap and the oil dipstick. It is not possible to get a negative reading on either one of those openings, but it should not be positive - meaning air blowing out.

The natural vacuum inside the intake manifold will draw a small amount of pressure from the crankcase, by design. If there were a large hose to the intake, the additional air would push the revs to breaking point.

So not having positive pressure is about the best you are going to get. A plugged PCT or vacuum line will cause the crank pressure to go positive. Same for a clogged oil separator.

On the older cars, the oil separator usually needed replacing by about 150K miles, mainly because the hoses degraded and cracked.





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