Radiator caps

southpw · Post by **southpw** » Thu Dec 15, 2016 6:02 am

I have an aftermarket radiator I have purchased used. It did not come with a cap. The filler hole is much smaller than that of the M38 diameter. My thoughts of easily going to the local auto store and comparing numerous on the shelf was just that, a thought. Shelf had 2 kinds. Upon asking the desk about more available and got the dreaded "for what vehicle?".
Anyone know how to measure for a rad cap and a site to purchase? I know I should get one that works at around 4psi but unsure how to identify the correct cap. My rad filler neck has an overflow tube. Not sure if cap should seal at the bottom of neck or around top flange?
Thanks
Brad

Post by **wesk** » Thu Dec 15, 2016 12:03 pm

I would start by contacting the aftermarket radiator's manufacturer or distributor. They may well have a set of installation instructions with a parts list.

If no joy with that then take the radiator to the parts store. Put a short length of hose on the overflow tube. Test fit caps until you get one in the correct PSI rating range that seals the seat below the overflow. Check this by blowing thru the hose. If it seals the seat the air will only escape out through the top surface of the cap. If it doesn't seal you will hear or feel the air escaping at the top radiator hose port.

RICKG · Post by **RICKG** » Thu Dec 15, 2016 12:36 pm

2X on what Wes said. A 3rd option might be a rad repair shop, a grizzled old rad repair guy may take one look at it and have the answer.

With the throw-away rads they put in todays autos the grizzled old guy is getting harder and harder to find.

southpw · Post by **southpw** » Thu Dec 15, 2016 4:09 pm

Thanks guys. There is a rad shop local to me that epoxy'd my tank. I will see what he says.
I cant find a manufacturer's name on the rad which makes it harder. I found an aluminum rad on ebay and contacted them about the rad cap.
Once the snow stops flying I will take a trip to Napa and see what they have. Only problem with Napa in Canada is everything is in a warehouse with just oils, etc in the actual store.

Hawkshadow · Post by **Hawkshadow** » Fri Dec 16, 2016 10:24 pm

X2 on just rolling up to the rad shop. I needed a new cap, the old guy took one look, walked inside, and 2 mins later I had a new one and was on my way.

4x4M38 · Post by **4x4M38** » Sat Dec 17, 2016 8:53 am

We are losing those guys every day.

One day we are going to be the grizzled old guys...

Post by **wesk** » Sat Dec 17, 2016 12:57 pm

Some of us do not have to wait for "someday".

A word of wisdom when you take the cap from the old grizzled guy take it home. Put it on the radiator and do the air flow tests I posted above. Also read the print on the cap for the rated pressure yourself just to make sure the old grizzled guy was not blind or just an old grizzled guy with no calling! Many later systems are 7 or more PSI but you need 4 1/2 PSI.

southpw · Post by **southpw** » Sat Dec 17, 2016 5:06 pm

Thanks. I will be taking rad with me and will confirm both things before purchase. I've spent $10 here and $10 there to many times on this project already and pieces sitting around doing nothing

4x4M38 · Post by **4x4M38** » Sat Dec 17, 2016 8:16 pm

"Welcome to the party pal." John McLain

southpw · Post by **southpw** » Wed Dec 21, 2016 5:36 am

Im noticing many of the rad caps are labeled in lbs, not psi. Would 4lb cap be the same as a 4psi cap?
I have not had a change to go to the rad shop yet but just dont want to get a correct fitting cap yet it is not the right pressure
Thanks

RICKG · Post by **RICKG** » Wed Dec 21, 2016 8:07 am

YEPPIRS!

southpw · Post by **southpw** » Wed Dec 21, 2016 10:37 am

Thanks Rick