# Engine Crankcase air pressure build up **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** chevrolet, trailblazer\ **Created:** [January 8, 2011, 11:18pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727 "2011-01-08T23:18:13Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![roller858791](https://avatars.discourse-cdn.com/v4/letter/r/a88e4f/32.png) [@roller858791](https://community.cartalk.com/u/roller858791)\ **Post date:** [January 8, 2011, 11:18pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/1 "2011-01-08T23:18:13Z")
I have a 2002 Chevy trailblazer with a 4.2 inline 6 cly. engine. The engine crankcase is building up air pressure and blowing oil out onto the engine. ---
**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\ **Post date:** [January 8, 2011, 11:45pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/2 "2011-01-08T23:45:38Z")
Try replacing the PCV valve. Cheap fix, and I replace mine every time I change the spark plugs. ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [January 8, 2011, 11:50pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/3 "2011-01-08T23:50:22Z")
Make sure the PCV system is not clogged. If it’s okay, then you have excessive blow-by from worn out rings. ---
**Author:** ![Rod-Knox](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Rod-Knox](https://community.cartalk.com/u/Rod-Knox)\ **Post date:** [January 9, 2011, 12:02am UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/4 "2011-01-09T00:02:49Z")
Check the oil level. If over filled it will blow out the dip stick tube. ---
**Author:** ![roller858791](https://avatars.discourse-cdn.com/v4/letter/r/a88e4f/32.png) [@roller858791](https://community.cartalk.com/u/roller858791)\ **Post date:** [January 9, 2011, 5:31pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/5 "2011-01-09T17:31:46Z")
I stopped by the auto parts dealer and they told me this engine is not equipped with a PCV valve. ---
**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\ **Post date:** [January 9, 2011, 7:43pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/6 "2011-01-09T19:43:23Z")
You’ll need a manual to determine how the crankcase is vented. Federal law will not let the crankcase be vented to the atmosphere like cars in the 60’s. But, if the system this engine uses to vent the crankcase is clogged or non-functional, pressure will build up and cause these issues. My Supra uses a ported vacuum line with no PCV valve. Some Volvo’s use a breather box that is baffled and ported without using a PCV valve. I’d be interested to find out how this GM engine does it. ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [January 9, 2011, 9:35pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/7 "2011-01-09T21:35:38Z")
This would be why I said PCV system and not PCV valve. ---
**Author:** ![waterboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/waterboy/32/764_2.png) [@waterboy](https://community.cartalk.com/u/waterboy)\ **Post date:** [January 9, 2011, 9:45pm UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/8 "2011-01-09T21:45:01Z")
[http://forums.trailvoy.com/archive/index.php/t-9838.html](http://forums.trailvoy.com/archive/index.php/t-9838.html) MTPockets, “There is no PCV valve used on the 4.2 engine. Fresh air from the throttle body is supplied to the crankcase, mixed with blow-by gases and then passes through the crankcase ventilation pipe into the intake manifold. The vacuum used to “sweep” the crankcase in that which is created in the intake manifold. When the throttle is opened manifold vacuum decreased. At this point in time, crankcase pressure are higher and crankcase gases rush down the ventilation pipe, into the engine and are then combusted together with the normal fresh air/fuel mixture. Also, GM also states that the crankcase ventilation has no serviceable components, so no maintenance of the system is required.” More responses in the link. ---
**Author:** ![roller858791](https://avatars.discourse-cdn.com/v4/letter/r/a88e4f/32.png) [@roller858791](https://community.cartalk.com/u/roller858791)\ **Post date:** [January 10, 2011, 4:26am UTC](https://community.cartalk.com/t/engine-crankcase-air-pressure-build-up/59727/9 "2011-01-10T04:26:07Z")
Hey…Thanks for all the help. I found out that in the plastic intake manifold the inlet port from the engine was plugged up and frozen. Upon further inspection this molded inlet port was not completely open from the factory molded component. I used a philips screwdriver to open up the plastic mold slag into the intake manifold. It probably was open just enough until years of routine driving which eventually clogged it up. I have cleaned and components, used engine degreaser on everything and all seems to be working now. Probably will have to change the serpentine belt soon…starting to squeek a little. Again thanks for the help.