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what causes oil to come up into the oil cap while the engine is running? the engine is in a 1970 stang. 302, 2V, c-4 trans. i have a pcv valve in the right valve cover and a push-in ford motorsports oil cap in the left. the oil cap has a place to put a hose that would go to the air cleaner, if my air cleaner had a place to connect it. right now i don't have a hose on it. it is blowing enough oil to make me mad on my chrome valve covers. what would cause this or what do i need to do? any ideas...
 

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You could have blowby due to worn rings allowing air to get past rings and push oil vapors out the cap. I have a 70 Coupe 302 2v 3 speed. My cap has a screen in it to filter the air that should enter this if blowby is in control and pcv valve is able to handle the normal amount of blowby.

If you plug the cap, and blowby is the problem, it will force oil out of every gasket it can!

Tom
 

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two choices..put a hose in the oil cap and connect it to the air cleaner..or get a cap with a mesh inside to control the vapors...'70's were designed to rebreathe the vapors..if you put on a solid cap with mesh..you will need to change it about every 6 months..as it becomes blocked over time the mess will start up again
 

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I agree with Teebone. I will also add thatyour valve cover should have some kind of baffle under the cap. The baffle helps greatly to reduce oil splash from reaching the cap.
 

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Since you have chrome valve covers, I'll bet that there are no baffles in them. The factory covers have a baffle/oil seperator under the breather & pcv holes. If you pull the fill plug out, and can see your rockers when you look inside, then there is your problem. Get a good set of covers with a baffle, and that should stop your oil problem if your engine does not have excessive blowby.
 

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I agree with Hemikiller and onetrickpony. You probably have no baffles in the valve covers. I can run my engine without the oil breather cap (open element filter on mine) and no oil will splash out. I use the Edelbrock "finned" valve covers. They have a nice BIG baffle under the fill/PCV holes. Putting oil in is slow because of them, but I can live with that.
 

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Hi compression engines, no only bad rings, can cause the extra blowby. If you have a stock 70 302, this is not your problem. But if it's been rebuilt with flat top pistons and/or small chamber heads, you will get more vapors sent through the "breather".
 
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My chrome valve covers both have baffles. I know that the oil cap needs some kind of vent in it, because I have tested that already. With the oil cap just plugged, I get some oil blowing out the dipstick tube. This leads me to believe that I probably have worn rings. I did a compression check and all cylinders checked good and strong. I don't get much oil blown out the cap, just blows a little out on the valve cover which P's me off. The oil cap I have is hollow. Maybe if I stuff something in there that will allow the engine to breath, but won't let the little bit of oil blow out. I think that if I run a hose to the air cleaner, it will just blow the oil up there, which I don't want either.
 
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