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Oil Fill Cap Vent

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caps oil vent
7K views 15 replies 4 participants last post by  leon1017 
#1 ·
I am interested in how you guys deal with the Oil Fill Cap Vent. On my 1979 CJ5 I have the "stock" oil fill cap which has the connector sticking out of the side. What the previous owner had done (and what is still in use today) is that I have taken a long piece of hose and connected it to the vent part of the cap and ran it all the way to the back of the jeep so that it vents out near the exhaust.

I know the other way to vent would be to do something with the valve cover, etc. but I am curious to know how you guys are handling the venting.

Thanks
 
#4 ·
Thanks for the pic Matt. My engine compartment does not have the factory air cleaner so either I go back to factory like yours, or vent it back into the aftermarket air cleaner? There is a knockout for it. I would just have to find a connector for it.
I am curious though, do you have much oil venting back into your air cleaner? Any at all? I know that there is a small "filter" in the oil cap itself, but that will only catch so much.
 
#5 ·
I am curious though, do you have much oil venting back into your air cleaner? Any at all? I know that there is a small "filter" in the oil cap itself, but that will only catch so much.
None. Since that is the intake side of the PCV, there should be a small amount of vacuum at the nipple on the oil-filler cap when the engine is running. In other words, the flow of air should go from the air cleaner thru the cap into the crank case, then out the PVC valve into the intake.

If you're getting oil thru the cap, then either the vacuum side of your PCV system isn't functioning properly, or you have excessive blowby from a tired engine.

Clear as mud?

Matt
 
#6 ·
That makes sense Matt. I am thinking more of a tired engine more than anything. I am just trying weighing my options as to what to do.

So, with the engine running i should feel a small vacuum at the nipple on the oil filler cap while engine is running. If there is none then what? Tired engine?
 
#7 ·
If there is no vacuum at the cap, then check the PCV valve. If it rattles when you shake it, then it's likely OK. If not replace it.

Also make sure the PCV valve is connected to a manifold vacuum source. Usually it's a large nipple on the rear of the carb, like the pic below.

Matt
 

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#8 ·
Okay, so now I think I have some additional issues to sort. I know for a fact that the manifold vacuum on the carb is capped. So there is no hose, or PCV valve for that matter going from the carb to the manifold. Would it be in my best interest then to put back in a hose based on your picture to get proper vacuum again?
 
#9 ·
Yes, you need a PCV valve attached to a vacuum source to properly vent the crankcase vapors. Otherwise, you will have an oily mist everywhere inside your engine compartment.

Here's what the PCV components look like. The grommet part # isn't correct, however.

Matt
 

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