Blow by

[Cheif Oceola]

My baby is a 91 YJ who I am giving some tlc to get her back in shape. Engine runs decent but I have oil being pushed out of my dipstick. There is a bolt missing in my header that is rusty in the threads where the bolt is missing, I think this missing bolt is part of the blow back issue. Any ideas how to stop this outside of a new engine? Should I just live with it till it dies?

 

[flatie46]

My baby is a 91 YJ who I am giving some tlc to get her back in shape. Engine runs decent but I have oil being pushed out of my dipstick. There is a bolt missing in my header that is rusty in the threads where the bolt is missing, I think this missing bolt is part of the blow back issue. Any ideas how to stop this outside of a new engine? Should I just live with it till it dies?

I had a cherokee with the 4.0 and it had quite a bit of blow by the whole time I had it. I put 100,000 miles on it and didn't have any problems. I don't think it was factory but from the valve cover there was a hose that run over by the air filter and down under the engine next to the frame to vent. It'd get oily down there and I'd wash the engine and frame every so often. I meant to put some kinda filter on it but never did. I think it was suppose to be run to the airbox with a PVC filter. To tell the truth I didn't worry about it 'cause I didn't think that engine would last that long. It's still going strong, had 365,000 when I traded it.

 

[Utah_jeepster]

The missing bolt in the header isn't the problem, first you need to get a tap and chase the threads in head so you can put a new bolt back into the hole.
Next you need to check and most likely replace your positive crankcase ventilation (PCV) valve.

Your crankcase is a sealed unit and the PCV valve allows the vapors to pulled from the top of the motor (also from the crankcase) and re-introduced back into the manifold to be burned.
When the PCV valve is plugged up the pressure in the crankcase can build and push small amounts of oil up and out of the dip stick.

 

[Cheif Oceola]

Thanks for the input!

 

[Bounty__Hunter]

The '91 is a CCV (Closed Crankcase Ventilation) system, Utah is correct on how crankcase vapors are to be burned by routing them into the intake.

Find the tube from the valve cover to the airbox or airtube. Pull this small tube from the airbox end and feel for vacuum sucking into the engine. If it's blowing air out, there's a problem with the CCV system. Let us know what you find.