Oil Filler Cap & PCV - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**lkt1954** · 07-04-2023, 06:49 PM

On my 70 C10 with a 350- automatic/air conditioning, each valve cover has a 1.25" hole.
I know one is for the PCV valve and it connects to the base of my EFI and the other is for the oil filler cap.
I've read multiple post and am still a little confused on which oil filler cap I need. Do I need the push in rubber cap or a breathable cap with a grommet in the valve cover?
Thanks

Dead Parrot · 07-04-2023, 08:53 PM

Most OEM PCV systems have the PCV valve in one valve cover with a hose that runs to the base of the carb(or in your case the EFI base).
The other valve cover has a hose that runs to a small filter in the OEM air cleaner housing.

My 68 Impala had the oil fill in the intake manifold. At some point that moved to a 2nd hole in a valve cover, which is how my 75 C10 (350/TH350) is setup. 2 holes in one valve cover 1 for the air vent, the 2nd for an unvented oil cap.

Guessing that since you have a EFI system, you also have an aftermarket intake manifold and probably lost the oil fill tube in the OEM manifold. If this is the case, you should use a vented oil cap in the valve cover opposite the one with the PCV valve.

Do you have the OEM air filter housing?

**lkt1954** · 07-04-2023, 09:49 PM

Dead Parrot- no it's an after market air cleaner. Also both the intake and valve covers are after market.

Dead Parrot · 07-05-2023, 10:38 AM

Quote:

Originally Posted by lkt1954

Dead Parrot- no it's an after market air cleaner. Also both the intake and valve covers are after market.

Then get a vented oil cap. PCV valve on one side, vented cap on the opposite side. You want the air to enter one valve cover, go through the rotating assembly and exit the other valve cover before being use as combustion air.

Do the valve covers have splash guards for the holes?

**lkt1954** · 07-05-2023, 01:49 PM

I'm not sure on the splash guards. My guess I will need a grommet for each side.

geezer#99 · 07-05-2023, 09:24 PM

Splash guards are called baffles.
They keep the oil inside the cover and let the fumes out to the pcv. The air in via the breather doesn’t absolutely need a baffle but can use one.
If you can look in the holes and see the rockers or valve springs then you have no baffles.
In that case they make baffle grommets like in the link in various sizes.

https://www.ebay.com/itm/385427949320

**lkt1954** · 07-06-2023, 11:22 PM

Thanks for all the help got everything ordered and even ordered baffled grommets to be safe.

07-04-2023, 06:49 PM	#1
lkt1954 Active Member Join Date: Dec 2007 Location: Dumas, Texas Posts: 188	Oil Filler Cap & PCV On my 70 C10 with a 350- automatic/air conditioning, each valve cover has a 1.25" hole. I know one is for the PCV valve and it connects to the base of my EFI and the other is for the oil filler cap. I've read multiple post and am still a little confused on which oil filler cap I need. Do I need the push in rubber cap or a breathable cap with a grommet in the valve cover? Thanks

07-04-2023, 08:53 PM	#2
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,506	Re: Oil Filler Cap & PCV Most OEM PCV systems have the PCV valve in one valve cover with a hose that runs to the base of the carb(or in your case the EFI base). The other valve cover has a hose that runs to a small filter in the OEM air cleaner housing. My 68 Impala had the oil fill in the intake manifold. At some point that moved to a 2nd hole in a valve cover, which is how my 75 C10 (350/TH350) is setup. 2 holes in one valve cover 1 for the air vent, the 2nd for an unvented oil cap. Guessing that since you have a EFI system, you also have an aftermarket intake manifold and probably lost the oil fill tube in the OEM manifold. If this is the case, you should use a vented oil cap in the valve cover opposite the one with the PCV valve. Do you have the OEM air filter housing?

07-04-2023, 09:49 PM	#3
lkt1954 Active Member Join Date: Dec 2007 Location: Dumas, Texas Posts: 188	Re: Oil Filler Cap & PCV Dead Parrot- no it's an after market air cleaner. Also both the intake and valve covers are after market.

07-05-2023, 01:49 PM	#5
lkt1954 Active Member Join Date: Dec 2007 Location: Dumas, Texas Posts: 188	Re: Oil Filler Cap & PCV I'm not sure on the splash guards. My guess I will need a grommet for each side.

07-05-2023, 09:24 PM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,523	Re: Oil Filler Cap & PCV Splash guards are called baffles. They keep the oil inside the cover and let the fumes out to the pcv. The air in via the breather doesn’t absolutely need a baffle but can use one. If you can look in the holes and see the rockers or valve springs then you have no baffles. In that case they make baffle grommets like in the link in various sizes. https://www.ebay.com/itm/385427949320

07-06-2023, 11:22 PM	#7
lkt1954 Active Member Join Date: Dec 2007 Location: Dumas, Texas Posts: 188	Re: Oil Filler Cap & PCV Thanks for all the help got everything ordered and even ordered baffled grommets to be safe.



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