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sealing cast iron hot water radiator

I picked up a couple nice cast iron radiators that I want to use to heat a room. Overall they are in really nice shape. We tested them, one is good (held 40PSI all day no issues)

The other leaked a little bit on 2 of the top joints even without pressure (just had it upside down and had the hose in one end and let it run out the other end).

We tapped it apart, using a wood block and a mallet, working each end a bit at a time. It was not hard to do. I was going to wire brush the nipples (they seem to be a light press between sections) and castings and press them back together. I am planning to use a 5/8 threaded rod in the end holes with a steel plate on the openings and use the nuts to pull them on.

I have 2 questions

1. what do I use to seal the nipples? I have asked around and have been told a high temp RTV would work, is that correct, or is there something better?

2. the nipples are still in one side of each section. should I get them out of both sides, clean and re-seal? I can turn a piece of alum just smaller than the ID of the nipple and just a tiny bit smaller than the OD and use a mallet to tap them out but do not want to damage them.. do I need to do this or not?

thanks in advance for the help!

I can upload pictures if that helps.

thanks again!


  • Jamie Hall
    Jamie Hall Member Posts: 22,924
    Yes, you should try to get them out if you can. Those nipples are intended to be a shallow taper press fit in the sections. If there is any corrosion on them or on the seats in sections, you can try to polish that off, but if there is any tracking they won't seal.

    Since they are a press fit, you can use a very thin layer of high temp RTV or engine gasket maker on them -- but don't overdo it. You need only a thin layer.

    Are there existing tension rods on the radiators, or provision for them? If so, better to use that, although your idea of steel plates and threaded rod will work. That said, don't go gorilla. Bring the nuts up hand tight, and then pull the sections together, and then back the nuts off, bring them hand tight again, and then no more than a half turn. Otherwise, when the radiator heats, the tension on those rods will become alarmingly high.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Big Ed_4
    Big Ed_4 Member Posts: 2,700
    edited October 2021
    You can split the section and with luck it would pull the leaky push nipple side will pull from the section . The last time I did this we used peratex to lube and seal the push nipple. ... If it did not work look for another or buy a new unit ..
    I have enough experience to know , that I dont know it all
  • cnyinthewoods
    cnyinthewoods Member Posts: 2
    Thanks guys, yes there are tension rods on it. I was going to use the threaded rod to press each section as we re-assembled it, as I did not want to try an press them all together at the same time.

    everything looks pretty clean and free of corrosion.

    I will turn up an alum shaft that will go inside the nipples and have a shoulder to push the nipples out.

    question Big Ed, did you mean Permatex? If so what version did you use?

    thanks again! I hope to be able to get this together in a week or so. I will let you know how it goes.
  • Jamie Hall
    Jamie Hall Member Posts: 22,924
    I'm sure @Big Ed_4 meant Permatex. Which version? I've only ever used the black...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • psb75
    psb75 Member Posts: 808
    They still make and sell push nipples. Might be worth a search...in case they are compromised from age or removal. Measure w/ calipers and verify w/ seller before purchasing. The RTV will help 'lubricate' during installation and for sealing when dry and pressed in place.