Coolant leak

[gonesailing13]

Just installed a new radiator cap on my engine and now notice coolant leaking from under the cap. Purchased the new cap from American Diesel so I know I got the right one. Any ideas ?

[BruceK]

What led you to replace the cap? They are very low psi.
The Lehman expansion tank has a meat tube inside it leading to the overflow. If that blocks,and they do(mine needed to be drilled clear),the coolant could look for a place to escape. A low psi cap could be that place.

[Bigsfish]

New parts can be defective.

[Tator]

Assuming that your engine has the overflow kit, make sure it isn't leaking from the overflow neck insert. Both of mine started leaking after 8 years of being installed. I had to pull the tanks and re-epoxy the neck. I thought it was a bad cap at first.

Tator

[Ski in NC]

Folks like to step on the caps considering placement. Often the brass gets bent a little and cap will not seal. Epoxy in a new neck and good to go.

And don't step on the cap.

[gonesailing13]

Did find a leak in the neck but unsure how to remove the old one and what kind of epoxy to use on the new one.

[Bigsfish]

I’m no mechanic like Ski but I have found a small amount of JB Weld or Matinetex works great on sealing small leaks (sometimes big ones too).

[kchace]

Originally Posted by gonesailing13

Just installed a new radiator cap on my engine and now notice coolant leaking from under the cap. Purchased the new cap from American Diesel so I know I got the right one. Any ideas ?

I replaced my caps and also ended up with leaks on both engines! The problem I had was the aluminum of the tank was corroded between the tank and the filler neck and that corrosion caused the filler neck to bulge inward - preventing the inner part of the cap from being able to seal at the inside bottom of the filler neck.

Installing 2 new filler necks solved the problem and restored correct operation of the expansion bottles.

Ken

[kchace]

Originally Posted by gonesailing13

Did find a leak in the neck but unsure how to remove the old one and what kind of epoxy to use on the new one.

The filler necks are removed by slicing them inside using a hacksaw blade then grabbing with channellocks and twisting/pulling them out.

Clean up the inside bore, making sure the new one fits correctly, then use JB Weld to glue into place.

After that is done, you run a long drill bit in through the expansion hose fitting from the outside to make a hole all the way through. Just be sure to position the filler neck into the tank far enough so that the hole ends up above the inner seat.

Ken

[Comodave]

Have the same problem on one of my engines. Coolant is always low, but never goes any further down than about an inch below the cap. Other engine stays full. Put a radiator tester on it yesterday and have a leak at the cap so I will be replacing the filler neck also.

[diver dave]

After a while the red metal that the cap seals onto can groove or pit. Even without feet involved!