Educate me: Radiator caps...

I bought a new coolant expansion tank (advertised for use on the '99 Miata). It came with a radiator cap that didn't have a pressure release spring:

Now the car I'm putting it in to ('82 Alfa GTV6) had a tank that had a radiator cap with a pressure release spring

(photo below)

My question was simple: Is it safe to use the non-sprung radiator cap or should I try to fit an appropriate "sprung" radiator cap (as I type this I realize I have the two sitting next to each other but have not tried swapping caps...)

Except my question isn't really that simple: Because if I put the sprung option on there then there isn't really a provision to dump the expanding coolant out a "dump line" and into an expansion tank in the event of over-pressurization (I'd probably have to add such a provision)

If I put the unsprung cap on there with no pressure release provision then I assume that the next pressure release system will be in the form the oldest/weakest coolant hose bursting.

If this is a replacement for a Miata, does that mean there's another point in the Miata's cooling system that will vent pressure in the event it starts running too hot?

Thoughts from the hive on this one would be much appreciated.

Thanks! -Bill

i may be wrong but it looks like you bought a overflow tank, a quick google shows 99 miata's having radiator caps on the radiator, therefore releasing pressure/coolant from the radiator to the overflow tank which isnt pressure sensitive so no need for a sprung cap. you can see the radiator vent line going to the metal tank.

you're right! Look at that...

Hey, either way it HAS to be better than the plastic piece-o-e36m3 I removed from the engine bay (unless someone says "oh god, don't run that there!)

This may get tricky...

The neck on your new tank will not accept a pressure cap. They require a seat at the bottom for the seal to act upon

You can cut your neck off and use a Canton neck and pressure cap though

When I made my stainless pressure tank I used that piece because it was cheap and easy

That's what I was thinking for a "plan b". I bet I can find a weld on bung like the top picture and call it macaroni.

Thanks guys!

Here's one on Ebay

A shade over $15 delivered

Ordered!

Thanks

Any time mate, good luck with it bill

iadr wrote:

Hungary Bill wrote: you're right! Look at that... Hey, either way it HAS to be better than the plastic piece-o-e36m3 I removed from the engine bay

Umm, you can see through metal? If not, I would disagree. Personally I can't see through metal.

I don't know that he could see through the yellowed OEM tank much better.

90's GM products with the LT1, LT4, and L99 engines all had cooling systems with a pressurized cap on the expansion tank..

So 92-97 Corvette, 93-97 Camaro/Forebird, and 94-96 Caprice/Impala SS/Roadsmasher.. i don't know about the Vette or Camaro tanks, but the Caprice tank isn't overy huge and is mostly rectangular..

m4ff3w wrote:

iadr wrote:

Hungary Bill wrote: you're right! Look at that... Hey, either way it HAS to be better than the plastic piece-o-e36m3 I removed from the engine bay

Umm, you can see through metal? If not, I would disagree. Personally I can't see through metal.

I don't know that he could see through the yellowed OEM tank much better.

You can see through them with a bright flashlight