Marine diesel heat exchanger leak, high temp sealer/adhesive for brass to cast iron.

[Rivertest]

I'm trying to repair a cast iron marine diesel heat exchanger which has a standard brass radiator filler neck. I suspected that it was leaking for some time so removed the complete unit and had it pressure tested locally by a radiator specialist, and sure enough it leaks where the expansion pipe comes out of the neck. The original hasn't been soldered in and they weren't to keen on trying to solder it. The neck has been sealed into the casting with some kind of putty so I was looking for a recommendation of a suitable product to use. I've bought a new standard brass neck as I suspect the old one won’t come out without damage. Dimensions of the replacement are identical. Any help much appreciated.

 

[Bornfree]

If its a tight fit, a loctite type product would do it.

 

[James1979]

Either something like devcon or hysol, depending what you can get locally, but my first choice would be solder / braze it in place. Silver solder would work well on that.

 

[Brad93]

where are you based?

 

[Rivertest]

where are you based?

Hi Brad, Honiton in Devon

 

[Rivertest]

Either something like devcon or hysol, depending what you can get locally, but my first choice would be solder / braze it in place. Silver solder would work well on that.

I haven’t tried to take it out yet. It’ll be interesting to see how exactly it was put in originally. Whilst a previous owner had put some sort of filler around the neck and also silicon there are signs of a hard sealant down inside the where the neck seats in the casting.

 

[Brad93]

if you go with an epoxy it will need to take the heat and moisture. Sure belzona will have something but make sure you are seated. I'd look for a radiator specialist.

Personally I think that could be soft soldered or silver soldered.

 

[mike os]

Hard to see why it wouldn’t solder

Most rads are soft soldered

Is it leaking from the pipe or the join between the pipe and the filler ?

The pipe was almost certainly soldered in originally

 

[Rivertest]

Thought I’d give it a go with a bit of heat and a couple of pry bars. It came out pretty easy and it looks like some sort of flexible sealant not silicon though.

 

[Rivertest]

Hard to see why it wouldn’t solder

Most rads are soft soldered

Is it leaking from the pipe or the join between the pipe and the filler ?

Hi Mike, take a look at the latest photos. It was leaking around the pressure relief pipe coming from the brass neck where it passes through the slot in the casting, hope that makes sense. The slot was also filled with sealant/putty around the pipe but I suspected this was where it was leaking as the sealant was cracked.

 

[mike os]

If the putty was around the pipe I suspect the putty is because it was leaking previously and someone had a go.

If it’s leaking from the pipe or around the pipe the pressure cap is passing, should only pass if failing or over pressured.

Probably leaking from the seal between parts? That’s the lowest point so would pass there?

I would start with the neck/ cap assembly.. make sure it works and isn’t leaking then look at a suitable bonding agent to refit.

 

[Rivertest]

If I was going to put money on it, the sealant looks and acts like Isopon or similar and amongst it all is an o ring which fits on the neck. It’s now cooled down and the neck is a good interference fit. So epoxy could be a good alternative?

 

[Brad93]

I'd clean the hell out of that and solder it with bakers fluid and 60/40

 

[mike os]

The o ring implies a mechanical seal was intended to me but no idea how it was to be retained.

I think on this one adhesive is probably the solution as you don’t want to desolder the relief pipe (assuming it’s soldered in)

A good quality epoxy putty I think with very clean, lightly abraded surfaces

 

[Bullet2012]

What pressure (psi) cap is fitted

 

[Rivertest]

If the putty was around the pipe I suspect the putty is because it was leaking previously and someone had a go.

If it’s leaking from the pipe or around the pipe the pressure cap is passing, should only pass if failing or over pressured.

Probably leaking from the seal between parts? That’s the lowest point so would pass there?

I would start with the neck/ cap assembly.. make sure it works and isn’t leaking then look at a suitable bonding agent to refit.

Thanks Mike,

The o ring implies a mechanical seal was intended to me but no idea how it was to be retained.

I think on this one adhesive is probably the solution as you don’t want to desolder the relief pipe (assuming it’s soldered in)

A good quality epoxy putty I think with very clean, lightly

I'd clean the hell out of that and solder it with bakers fluid and 60/40

What pressure (psi) cap is fitted
Mike, can you recommend a good putty?

Brad, tbh I’d rather stick with the same sort of method to refix the neck. The rad people that tested it also thought that using the original method would be easier. The heat exchanger is circa 1996 so using epoxy will hopefully be a better alternative to the original goop.

 

[mike os]

Devcon would be my normal go to but it’s only good to about 120c iirc

This may be sufficient… no idea how hot it gets

If you need hotter then a search fit high temperature epoxy should give you options

 

[W.olly]

Can an RTV sealant/adhesive be used ?

 

[gt6s]

JB Weld THE SLOW CURE ONE. The rapid one does not like heat. Same aplies to Araldite even the slow one is nowhere near as good as it used to be. I would definily advise slow cure JB Weld.. I know for sure it works with hot water.

 

[brightspark]

belzona is the best but big £££££££