Hey, I've seen some guys replace the the oil filler cap on their valve covers with a breather cap...is there any advantage to this? What does it do? I'm just curious if this is something that I should be doing & am not aware of 
Valve Cover Breathers...Whats the point?
- Thread starter hamonkeiser
- Start date
BlackFox5.0
Founding Member
It's more of carbed car thing, it lets in unmetered air into the engine on efi cars. Some supercharger guys run them because we constantly blow air even at idle into the crank case if you have that tube connected from the valve cover to the TB
Blue Thunder
15 Year Member
An engine requires positive crankcase ventilation to evacuate any gases formed by the normal blow-by effects of combustion on the piston rings. (If not eliminated, those gases will contaminate the engine oil, reducing its lubricating and cleaning properties)
So anyway, the engine needs an outlet side of the system and an inlet side. Engine vacuum sucks air from one valve cover and the breather on the opposite valve cover filters in fresh air. The factory setup uses a PCV hose on one valve cover, and the opposite cover has a grommet with another hose leading to the air filter housing. The fill cap is just a fill cap, since that particular PCV system is complete even with the fill cap closed.
If you eliminate the hose leading from the grommet to the air cleaner housing, (such as when you install an aftermarket air cleaner) you need to install a breather in the valve cover to take its place. Some aftermarket valve covers only come with 1 hole, so then you'd need to buy a combination breather/oil filler cap on that side.
So anyway, the engine needs an outlet side of the system and an inlet side. Engine vacuum sucks air from one valve cover and the breather on the opposite valve cover filters in fresh air. The factory setup uses a PCV hose on one valve cover, and the opposite cover has a grommet with another hose leading to the air filter housing. The fill cap is just a fill cap, since that particular PCV system is complete even with the fill cap closed.
If you eliminate the hose leading from the grommet to the air cleaner housing, (such as when you install an aftermarket air cleaner) you need to install a breather in the valve cover to take its place. Some aftermarket valve covers only come with 1 hole, so then you'd need to buy a combination breather/oil filler cap on that side.
Ok...so if I still have the hose leading from the oil filler tube to the EGR Plate, a breather wouldn't be necessary. Right?
25thmustang
Mustang Master
My car had horrible blow by when the rings went, and adding the breather greatly helped this out!
ok then here is my deal. i have a carbed engine and i used to have chrome valve covers with a pcv valve hooked to the air cleaner to the left cover. the other cover had a filter/filler cap on it. now i have the stock 87 valve covers with the filler tube and the little nipple coming off of that tube. what can i do to keep these covers and have a pcv system hooked up.do i just drill a hole in one cover and put a grommet and a pcv valve in it. or can i just get an inline pcv valve and hook it to the air filter and the nipple on the filler tube.
Blue Thunder
15 Year Member
dastang2 said:
The way the chrome covers were set up then, the air cleaner was doing the pulling, whereas, I run the hose from the pcv valve to a vacuum port on the intake. (I put a T fitting in the hose that feeds the power brakes) The air cleaner doesnt have anywhere near the vacuum pull, especially at idle.
Here's a quick sketch I threw together:
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