Vented Radiator Cap / Partial Pressure Coolant System...

[7milesout]

Guys,

As I understand, maybe all of the A-Body cars came with a Partial Pressure cooling system. I had never heard of it before, so maybe some of you guys haven't either.

It's determined simply by the radiator cap. A partial pressure coolant system has a radiator cap with a gravity controlled vent. Meaning, with a cool system, there's a vent that hangs open on the bottom of the radiator cap. And the coolant system will not build pressure until coolant warms up enough to touch the vent. The vent is closed by coolant as it rises (from heat) and pushes the vent closed.

At that point, pressure builds in the system and the radiator cap works in the way it does now, opening to vent out coolant to maintain a set pressure … set by the spring force of the radiator cap.

Nowadays, these vented caps aren't used much or at all (on new cars) to my knowledge. It's now full pressure coolant systems. Meaning, from the moment the coolant starts to warm, the pressure builds. I don't believe the current radiator cap on my Scamp is vented.

I will be changing the thermostat and radiator cap when I change intakes.

Does anyone here run a vented radiator cap? Summit sells one sure enough, it's part number SNN-10231.

 

[Dana67Dart]

Go with the stock radiator cap and what ever pressure it calls for. I believe the newer cars are using a closed system not necessarily a uncontrolled pressure system.
My 2007 ford taurus has a closed system and the cap is a 16lb cap that fits on the (what looks like an overflow of sorts)

 

[7milesout]

I've got a 1970 Plymouth (Valiant) service manual. It's the closest thing I have to my 1972 Plymouth (Valiant) Scamp. And it states to use a 16 psi vented cap. And that's what I will use. Which is what the Summit part number is.

 

[toolmanmike]

Each pound of pressure raises the boiling point 3 degrees. The whole system is pressurized.

 

[mderoy340]

Guys,

As I understand, maybe all of the A-Body cars came with a Partial Pressure cooling system. I had never heard of it before, so maybe some of you guys haven't either.

It's determined simply by the radiator cap. A partial pressure coolant system has a radiator cap with a gravity controlled vent. Meaning, with a cool system, there's a vent that hangs open on the bottom of the radiator cap. And the coolant system will not build pressure until coolant warms up enough to touch the vent. The vent is closed by coolant as it rises (from heat) and pushes the vent closed.

At that point, pressure builds in the system and the radiator cap works in the way it does now, opening to vent out coolant to maintain a set pressure … set by the spring force of the radiator cap.

Nowadays, these vented caps aren't used much or at all (on new cars) to my knowledge. It's now full pressure coolant systems. Meaning, from the moment the coolant starts to warm, the pressure builds. I don't believe the current radiator cap on my Scamp is vented.

I will be changing the thermostat and radiator cap when I change intakes.

Does anyone here run a vented radiator cap? Summit sells one sure enough, it's part number SNN-10231.

I run the 10231 on a closed system.

 

[67Dart273]

I've got a 1970 Plymouth (Valiant) service manual. It's the closest thing I have to my 1972 Plymouth (Valiant) Scamp. And it states to use a 16 psi vented cap. And that's what I will use. Which is what the Summit part number is.

Juz' sayin, you can download a 72 and other manuals free from MyMopar. That manual and several others on there came from the guys right here

I don't see that the cap matters. Pressure, yes, but "partial or full" no

 

[7milesout]

67Dart273 - Believe it or not, I don't know that I've ever heard of or been on that sight before. So thanks for that. And I found a 72 model service manual. As for the thermostat and radiator cap info … it's virtually the same info as in the manual I had.

But either way, that's a great manual. I'm going to read through it like a novel. Not that I'll understand it all or be able to do much of it, but it's a heckuva good read … for a car junkie nerd like me.


7milesout