exhaust comming out of oil cap

[RyanD]

I was messing aroun with my ac system with the car running and i got curious and took my oil cap off. I noticed exhaust comming out of it

Is this normal?

[Jarrett]

I doubt it's exhaust if your engine is running well. The crankcase is a pressurized environment due to the fast moving parts inside it an the continuously changing displacement. When your cylinders displace volume that volume comes from the crankcase. That's why we have crankcase vents and a PCV valve. Now might be a good time to verify the functionality of the PCV valve.

[BurtonRiderT6]

I dont think it's exhaust, pretty sure its just air pressure getting pushed out from the moving components. Yes it's normal.

[RyanD]

I doubt it's exhaust if your engine is running well. The crankcase is a pressurized environment due to the fast moving parts inside it an the continuously changing displacement. When your cylinders displace volume that volume comes from the crankcase. That's why we have crankcase vents and a PCV valve. Now might be a good time to verify the functionality of the PCV valve.

It smelled like exhaust.

How do i check my pcv valve?

[RyanD]

I dont think it's exhaust, pretty sure its just air pressure getting pushed out from the moving components. Yes it's normal.

I read somewhere it was called blow by so i got worried

[10thAnnivCB7]

mine has been doing that since i got it and thats what the PCV is for. I hope its normal lol

[oyajicool]

There is blow-by on every engine, new or old. Older ones tend to have more blow-by than new ones.

As long as your engine is not using excess amount of oil and have good compression on all cylinders, your engine should be good.

[BurtonRiderT6]

Blow by I believe is more so air blowing by the rings causing a loss in compression. I'm pretty sure you are ok though.

[oyajicool]

You can place a piece of paper on the oil filler opening and see how much air is coming out, due to blow-by.

[Fleetw00d]

The pistons moving up and down don't create a net flow of air out of the crankcase. When two are moving up, the other two are moving down at the same rate, so there is a lot of air movement within the engine, but the pistons are not directly pumping air out of the crankcase. The air coming out of the valve cover is primarily leakage past the rings (blow by). This includes air leakage during the compression stroke as well as exhaust leakage during the power stroke. It will normally at least smell like oil. As previously indicated, if your engine is running well and compression is good, then you should be OK. If compression is low, then you may indeed be smelling exhaust.