# Valve Cover Breather Cap Leaks Oil at WOT



## MaL (Jun 12, 2008)

I'm breaking in my rebuilt original 1966 389 on my GTO.

I have stock valve covers and (oil) breather cap. I've noticed when I get WOT I develop some smoke coming out from under the hood.
When I inspect everything, I see that oil is coming out of the breather element of the bottom side of the cap.
I took the cap off and peeked inside and found the oil baffles are not there. After 3 machine shops, I'm not going to attempt to figure out where they went.

So what's the best fix here? Either get replacement baffles and hope the rockers aren't too far from stock so it all fits or get a cap that doesn't breathe?


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## PontiacJim (Dec 29, 2012)

MaL said:


> I'm breaking in my rebuilt original 1966 389 on my GTO.
> 
> I have stock valve covers and (oil) breather cap. I've noticed when I get WOT I develop some smoke coming out from under the hood.
> When I inspect everything, I see that oil is coming out of the breather element of the bottom side of the cap.
> ...



Pontiac valve covers don't have baffles. You shouldn't have any oil coming out of the breather. Check to make sure that it is not as simple as a bad seal on the underside of the breather or wrong breather fitment. Oil coming out might also indicate a problem under the cover. I would pull the cover to take a look first, then if all looks good, have someone fire it up (while still cold) for about 30 seconds or so so you can see what is going on while it is running. Keep rags handy as it'll get a little messy and you don't want to do this with a hot engine and have fire.

Might be a rocker with an enlarged or worn out oil spurt hole in it directing the oil right at the breather. Assume you have the 60 psi oil pump and not the 80 psi which could be pushing too much pressure. 

DO NOT close off the breather hole as an engine builds internal pressure as the pistons go up and down and you will push oil out the dipstick and probably blow out a gasket somewhere on the engine. If anything, you want to add another breather to the opposite side. Take a look at this 389 valve cover on Ebay with the extended breather as this may be an option: ORIGINAL 1964 PONTIAC GTO 389 CHROME VALVE COVERS - | eBay

Hopefully you don't have an internal problem where the rings are not fitted correctly and you are having excessive blow-by. You might get a little as you say you are breaking in the engine, but it should not take long to seat the rings.


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## anguilla1980 (Sep 29, 2016)

This is a fix presuming there are no other "problems" causing it:

https://www.summitracing.com/parts/mrg-6002

It will really help seal the piston rings to prevent blow by and excess crankcase pressure. Been an old racers trick for at least 60 years...

My car does this too but since I hardly ever do full throttle runs, I'm not too worried about it and just wipe off the valve cover after I do.


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## pjw1967 (Mar 10, 2014)

I will try to post the diagram later. In the '67 shop manual it shows how the air flow through the PCV system reverses under WOT. There's little or no vacuum so guess the crankcase pressure builds up forcing some oil to exit through the breather cap. I do exactly what anguilla80 does. Wipe it off and keep pounding the throttle. FYI, been wiping that off for 22 years.


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## MaL (Jun 12, 2008)

I'll probably get an extended breather for now until there's more mileage on the new engine. Seems to be the simplest first step and go from there.

Thanks for feedback!


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## MaL (Jun 12, 2008)

I located and installed original oil guards that went missing, as I originally posted.
I'm hoping this will make a less direct path for the oil to come out of the breather cap.
I'll update soon on how it works out.

Missing-


Installed-


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