MTFCA Forum

The threads on the radiator filler on my 21 touring. I don,t believe they are stripped but just worn. I have researched the forum and not have found a answer. Has anyone had experience with restoring the threads on the filler neck?

I'd think the radiator neck wall is too thin to allow restoring the threads. There's very little metal to work with. Replacing the neck is one option.

Some past discussions didn't have an answer to the filler neck other than chasing the threads but questioned the threads of the cap. Have you tried a different cap to see if it feels different? Is it an original or repro cap?

one or two wraps of Teflon tape will be invisible, will secure the cap, and (because it is not a tapered pipe thread) will not tend to shred.

Scott_Conger wrote: ↑

Sat Jan 21, 2023 1:01 pm

one or two wraps of Teflon tape will be invisible, will secure the cap, and (because it is not a tapered pipe thread) will not tend to shred.

I agree with Scott. His suggestion was going to be mine until I saw he had already suggested ti. A new cap with fresh sharp threads mis helpful. I had the same problem with a T radiator and ended up having a radiator shop, replace the neck with a new one.

Hi George,
I once pick up a cast brass cap that didn't fit any of my radiators ( was to tight ) One day I was working on a T that had a Moto-Meter
that would not stay tight. I took the Moto-Meter off and the cast cap fit perfectly. That cap may have been one that the hot rod suppliers
like Speedway sells. Might be worth a try, if it works out let everyone know.
Craig.

I’ve found that on worn neck threads slowly and carefully thread the cap on. Worn threads can be caused by cross threading the cap on to many times and it eventually smoothing the threads down. It doesn’t take but a thread to do it and it’s hard to tell that’s you’ve done it.
My opinion of course but you can use a used cap that will thread better. If you have a decent original use it instead of a repo. Some of them don’t always work well if at all.

One way to fix it, but will look awful, however, a typical back yard fix would be to use a hack saw on the filler. Cut part way down almost to the end of the threads and then wrap around the threaded area a hose clamp and tighten enough to compress the neck to keep the cap on. Remember this is a back yard fix and if you want the car to look good a new neck would be required.
Norm

The radiator necks can sometimes swell a bit and flare out. They can also crack and split. Coupled with worn threads, and you've got your problem. Scott's teflon tape idea is great. Maybe also consider squashing the cap a bit to make it out-of-round, which may give some thread engagement in a couple of spots and be just enough to hold the cap on. This assumes you're using the stock cap and not a motometer. And obviously, if you go that route, don't go so far as to visibly deform the cap. I'm thinking it shouldn't take much movement to make it work.