When I say negative pressure, there is enough vacuum in the crankcase to make it difficult to remove the oil fill cap while the engine is idling (if i remove the dip stick it sucks like a hover),the car has smoke or steam coming out the exhaust ,i have just fitted the engine over the weekend and its a 2002 polo engine anyone any idear what the problem may be ? im going to do a compretion test tomorrow to see if its a blown head gasket but there is no water in the oil and i dont think it loseing any water

Could be a blocked breather...

I thought blown gaskets made positive pressure not negative

When the Land Rover TD4 crankcase gauze filter blocked it created positive crank pressure and blew oil past the crankshaft seal.


Once cleaned and replaced with the BMW cyclone filter, it stopped dripping and all returned to normal.




Take the cap off and run the engine, and put your hand over the hole, suck or blow as they say ?

Blocked breather would cause positive pressure . The thing I can think of is a connection to the inlet manifold causing crankcase vacuum. Doubt if it is due to low compression

Sounds like PCV valve problem, I'm sure google will get you pictures and symptoms.

Cheers
Davie

Many cars run an electronically (or sometimes pneumatically) switched crankcase vent straight to the plenum. If your valving has failed it'll suck most of its air through the crankcase. This is a problem on a number of levels.

Probably the diaphram in the oil breather,letting it suck crank gases instead of from air filter blank the manifold connection and vent the breather to a catch tank

quote:

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Originally posted by GOJO
Probably the diaphram in the oil breather,letting it suck crank gases instead of from air filter blank the manifold connection and vent the breather to a catch tank

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done a compretion test and all was ok but all plugs were wet with oil (but i worked out the the oil was coming from the rocker breather into the throttle body so thats no suprize)

Which engine?

sorry its a 1L MPI engine
im going to remove all vacume hoses and flush them


[Edited on 16/10/12 by thunderace]

video


http://www.youtube.com/watch?v=D7nksEmK3EY&feature=g-upl

The way the idle speed changes would suggest that it's definately linked to the inlet. Not much help sorry

Cheers
Davie

Older systems had a very small pipe to let any positive pressure into the inlet but later cars have a much larger flow rate , lots of bm,s do a similar thing . Dirty breathers are common on these so clean them out and see how it drives . The idle valve compensates for the change in vac when you open the filler and it still idles so its not a major issue .