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Re: crankcase pressure, odd question ALL 1989

posted by  someone claiming to be Don Foster on  Sat Mar 3 03:37 CST 2001 [RELATED]

Randy --

When you remove the oil cap you'll definately have fumes "puffing" from the valve cover. But at the same time, you'll have fresh air "puffing" onto the engine. These are the pressure pulses from the pistons oscillating up 'n down. For an ordinary engine in good shape—and with a good ventilation system—the net effect is a slight vacuum. (The puffing is kinda like an AC signal riding on a DC offset.)

To determine what's what, you must make a measurement.

"...either the Bentley or Haynes manuals even show the plug on the back of the head?"

Dunno — never looked at the manuals. The picture I posted is of an '86 B230F from a 245. The plug fills the hole that accepts the distributor when this motor is used in the 700/900 car.

If your plug popped, then you might want to measure your crankcase pressure. If you don't have a gauge (sometimes they're cheap on eBay) you can easily configure a water manometer.





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