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I bought a new overflow tank and cap for a 78-82 and it leaks around the cap all the time when driving. I have gone as far as adding EPDM rubber to inside of cap as a seal and it leaks less but still leaks. I decided to figure out a fix and found some rubber silicone plugs off amazon in 40.3mm after measuring. They are a real tight fit so I doubt it will be able to leak now and can still be pulled out. Just thought I would offer this out as it’s been a real annoyance for me. The replacement plastic Cap looks like it expanded and flared out from the under hood heat. The silicone plugs off should be good for alot more than it will see and can still be removed. If the cap was longer I would thread it on over.
I’ve been using this red plastic plug that came on a new power steering pump for another car. It says CAPLUG 17 on the back. The hard plastic doesn’t seal as well as silicone, but it’s good enough for the overflow tank, and the cap fits over it.
Charlie
I think you are looking at the wrong cap with your issue.
The overflow tank barely needs a cap; nothing should come out unless it's a bumpy road, slosh.
Your overflow tank is under pressure now, for some reason. The overflow tube is constantly pressurizing the tank.
What is the condition, age and number of pounds of the radiator cap?
I think you are looking at the wrong cap with your issue.
The overflow tank barely needs a cap; nothing should come out unless it's a bumpy road, slosh.
Your overflow tank is under pressure now, for some reason. The overflow tube is constantly pressurizing the tank.
What is the condition, age and number of pounds of the radiator cap?
The overflow isn't pressurized, its just road slosh. My level is at the min when cold and I don't think it even reaches Max when hot. The rad is basically brand new Entrophy dual row aluminum, the cap is a new 16lb and not leaking and I've tried two new ones just to be safe. Its leaking around the overflow cap when I'm driving around as the roads are windy and bumpy. The cap can't even be tightened by hand as it just spins off so I know its not sealing at all. It also probably loosens more as things heat up. Radiator temps are also almost always below 190*F even with the turbo and underhood heat thanks to the radiator and the Spal Brushless 16" fan with Dewitts spal shroud.
Thanks for the info, just ordered one. I have the same problem of coolant sloshing out of my 82 tank when autocrossing.
no prob. I took the car out yesterday on its normal trip and when I got back no leaks. I pulled it out and all under the plug was coolant so it was sloshing all around.
you might also want to extend the vent which mine was leaking out of also from sloshing. With the new tight plug and the extended vent I have no more leaks.
for the extended vent I heated a 1/8 npt 90 brass fitting with a torch and pressed it into the vent. Sealed it with high temp RTV and added a few inches of silicone hose. The top of the vent is now right at the underside of the top fender underside.
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Leaking 78-82 overflow tank cap fix
