Radiator Caps

[rodneym]

It seems like the more I ask, the more (different) types of answers I get...

What kind of caps do we use on the expansion tank? Vented or non vented?

My setup I think is typical. I only fill using the expansion tank. No cap on the radiator istelf, it's plumbed to and from the tank. If the heat/pressure goes up, coolant goes to the tank, and if too much, out the 'relief' hose when the cap gets opened. Right?

The vented cap has a metal button that simply hangs below the rubber spring loaded disk. The non vented (what I'm used to seeing) has the metal button that is touching the rubber but can be gently pulled away from the rubber.

So what do I/we use? My original is misplaced. I now have a billet specialties one on there which I'm pretty sure is non vented. It's working properly but who can explain the difference?

Any help out there?

Thanks,

rodneym

[Archrms]

I believe the caps without the second valve are used for over-flow type systems, where it lets coolant expand out of the system into an over flow tank, but does not allow the coolant back into the system. The caps with the second valve are used with recovery type systems which allows coolant to expand into a recovery tank, then return to the system as the engine cools down. Hope this helps.

[Rick Parker]

Caps that are intended for recovery type systems will have a rubber seal around the perimeter of the cap that seals on the top of the neck as well as on the smaller hole (approx 1.25" dia) into the radiator. As the coolant expands with heat and creates pressure it lifts/forces open the "plunger/seal" on the smaller hole and coolant exits the radiator and or surge tank. It will then flow throught the overflow hose and either onto the ground (non return) or into a sealed tank (return type) that will itself often have a radiator cap on it (rated higher than the cap on the surge tank or radiator). On the sealed system when the coolant in the engine begins to cool it "Shrinks", taking up less space in the radiator and with the system sealed it pulls coolant out of the sealed tank and past the metal button you speak of.

[Bernica]

This question shows up all the time. If someone is able, they should post pics of both types to put it to bed..m2c

[patrickt]

Originally Posted by Bernica

This question shows up all the time. If someone is able, they should post pics of both types to put it to bed..m2c

Here you go (mostly the second page): Overflow Tank question

[rodneym]

Patrickt,

On the thread you linked, your last post/picture shows what I believe most of us use.
BUT, Stant sells caps rated at the same pressure, that say 'Vented'. When I pick it up, that little button (lower most part of the cap) just hangs loose about a quarter inch. If both caps are placed upside down like your pic, you won't see the difference.
The caps that don't say 'Vented' have the button that touches the smaller rubber piece and is slightly spring loaded.
I understand how the expansion system works but I don't necessarily see how the button being spring loaded affects use, all I know is that the 'Vented' caps have a dangling button.

Am I in the Twilight Zone on this?

Rodneym

[patrickt]

There all going to be "vented" in that when they reach their maximum pressure they will allow steam/coolant to blow out through the cap. Mine has done that when my fans failed. What a plain vented cap won't do is allow coolant to be sucked back in to the cooling system as it cools and contracts. That's where you need a coolant recovery type cap and a coolant recovery system (of which I have neither). If you are not sure whether or not you have a recovery type cap, the way you test it is with the "Putnam Suck Test" as outlined in the referenced thread.


EDIT -- They might be using the term "vented" to also mean they have the little lever on the top that lets you pull it and blow off steam as well.

[patrickt]

No promises, but this sounds reasonably accurate... and I took it right off Amazon.com for the Stant 10331 Lev-R-Vent Radiator Cap - 16 PSI Vented http://www.amazon.com/Stant-10331-Le.../dp/B000B8LKZ0

Stant LEV-R-VENT radiator caps fit in the smaller spaces of today's engines, while providing a pressure release lever and may fit on applications where older, larger-shell caps may not. A tab on the bottom of the lever interlocks with the filler neck to prevent removal of the cap until the lever is lifted. When the lever is lifted, the entire pressure valve is lifted off the lower sealing seat in the filler neck, harmlessly venting pressure through the overflow tube.

[rodneym]

Patrickt,

The Lev R Vent is a completely different animal. And come vented and non also.

My cap is like yours on your exp tank (and I'm sure like most people's) but when I saw 'VENTED' on the cap it got me thinking .

Thanks for the responses.

rodneym