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Old 29-04-2020, 12:30   #1
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Sealant for heat exchanger

Hi everyone
I have a Volvo MD30a (1985) engine that is leaking coolant out of the end of the raw water heat exchanger housing. It's design is a tube with a single middle bolt to secure an end plate.

The exploded parts diagram can be found here:
https://www.marinepartseurope.com/en...-26-18147.aspx

The main heat exchanger housing has corroded enough to cause small leaks that are currently manageable but I need a solution for when the whole thing blows apart.

Currently I also cant take the exchanger apart as it is mostly sealed by corrosion and no lipseal, oring or gasket will fit once its apart.
Has anyone had any success with some sort of hi temp/pressure sealant on their heat exchanger? I don't want to mess with it unless I hear of a long term solution from someone.
Thanks
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Old 29-04-2020, 16:42   #2
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Re: Sealant for heat exchanger

Once you remove the corrosion, you can build up the area with high temperature epoxy. There are fillers that make the epoxy like putty or peanut butter. You build up in a few layers to the original size and shape. Maybe with a little sanding or filing.
Another way is have a machine shop bore thru the corrosion and make a sleeve.
And another way might be sanding it smooth and use oversize orings.
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Old 29-04-2020, 17:08   #3
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Re: Sealant for heat exchanger

Another vote for high temp epoxy.

You should be seeing about 190 degrees at full temp. 212 worst case scenario.

It just has to be waterproof and able to withstand those temperatures.
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Old 29-04-2020, 17:32   #4
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Re: Sealant for heat exchanger

This high temp epoxy you speak of with fillers, AKA metal set or JB weld?
Epoxy with aluminum powder.

https://www.smooth-on.com/products/metalset-a4/

Available I’m sure on Amazon, better than JB weld

At best I’d say a temp solution, don’t go far and have towing Insurence
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Old 30-04-2020, 09:19   #5
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Re: Sealant for heat exchanger

Firstly, that situation is not high temperature or pressure.
As possible solutions:
A- Catch the drips in something until a permanent solution such as heat exchanger replacement can be carried out while in port.
B- As a temporary solution dismantle, clean, then repair as required the damaged areas using appropriate epoxy and similar based materials then reassemble using good quality RTV silicone sealant as needed. Leave for 24 hrs. before testing or putting back into service. Then arrange for replacement of the heat exchanger as needed.
This is just a normal maintenance item and should never have been allowed to reach this state in order to maintain seaworthiness.
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Old 30-04-2020, 09:42   #6
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Re: Sealant for heat exchanger

Based on first hand experience with same issue on Yanmar 4Jh4AE engine, two potential solutions for you. IF you thought you wanted to make a proper repair, you could remove the round plate, carefully clean up the mating surface and corrosion and then use JB Weld to first fill in the pitted areas. Thereafter you will perhaps need to build up the surface against which the round cap lies. If you do this, it will necessary to then carefully hand grind the JB Weld repair area with a fine file, specifically the mating surface so that it is plumb, plane and flat. It can be done...my repair has been in service for more than 600 hours of run time since with no issues. BTW, it will probably the case that the bolt holding the plate in place will be difficult to free up as it is probably stainless and the threaded boss inside the heat exchanger may or is probably aluminum and the galvanic reaction between the dissimilar metals has frozen the bolt in its threads.
So, there is an alternative solution that will probably adequately suffice. The dry section of my hot exhaust system incorporates a bellows assembly to accommodate vibration. It is clamped in place with clamps made for diesel exhaust systems which are common on semis. I used a Red HIGH Temperature RTV Silicone, Type 650, VersaChem. P/N 65309 (www.versachem.com) to seal and thus eliminate hot exhaust gas leakage from the clamped in place bellows assembly. The exhaust gas temp which is about 5 downstream of the manifold exhaust is an infrared measured 300 degrees F. This treatment has been in place for more than 500 hours with no degradation or exhaust gas leakage. Your manifold is highly unlikely to experience temps anywhere nearly as high as that, so this may well be a workable solution for you.
Good luck.
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Old 30-04-2020, 09:48   #7
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Re: Sealant for heat exchanger

I am a big fan of JB Weld. I wish it was a little thicker so it didn't run but it will definitely take the heat on the heat exchanger without a problem. I had the pipe that leads out of the mixing elbow of our engine break. I repaired it with a combination of JB Weld and fibreglass tape. I bought a new pipe but ended up keeping it in reserve. The repair lasted from Brisbane all the way back to Canada with no change in its appearance.d
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Old 30-04-2020, 10:04   #8
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Re: Sealant for heat exchanger

I don't have any suggestion for the leaks in the exchanger housing.


But for the gasket you might consider high temperature RTV gasket maker.


Something like this is resistant up to 650degF, and it remains flexible:
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Old 30-04-2020, 10:50   #9
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Re: Sealant for heat exchanger

I second the motion for Permatex Gasket repair, there's a number of them available, just have to read up on which one suits your application. Used it many times over the years on different things and works great!
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Old 30-04-2020, 10:55   #10
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Re: Sealant for heat exchanger

Quote:
Originally Posted by wannacat View Post
I second the motion for Permatex Gasket repair, there's a number of them available, just have to read up on which one suits your application. Used it many times over the years on different things and works great!



I recommended the red high temperature variety but in reality the less expensive type will likely be fine. Most (all?) silicone can handle boiling water. Pretty sure they all handle 400+ deg F, but check the technical documentation to be sure.



They make one specifically for water pumps and thermostat housings:


https://www.permatex.com/products/ga...licone-gasket/
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Old 30-04-2020, 15:24   #11
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Re: Sealant for heat exchanger

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Originally Posted by a64pilot View Post
This high temp epoxy you speak of with fillers, AKA metal set or JB weld?
Epoxy with aluminum powder.

https://www.smooth-on.com/products/metalset-a4/

Available Im sure on Amazon, better than JB weld

At best Id say a temp solution, dont go far and have towing Insurence
DO NOT buy Metalset from the only seller I found on Amazon. $57 for an 11 oz set. At least they offered free shipping.

Found it online from several aircraft supply companies for under $20 but shipping wasn't free. I finally ordered it from skygeek.com which came out to about $20 with shipping and FL sales tax. Never dealt with the company before so hopefully the order actually shows up. Will report back when it arrives.
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Old 30-04-2020, 15:42   #12
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Re: Sealant for heat exchanger

When I purchased my boat, the zinc for the heat exchanger was ignored by the previous owner or the dealer (it was taken in on trade and sat for a year before I bought it). The HX is cast aluminum with bronze end caps, about as bad as you can get for galvanic corrosion. I had about an half inch of metal that was gone from the aluminum side. I found it when I ran a salt flush, as the salt crystals were sealing the leak. At the time, I couldn't find a HX so I repaired it by taking it out and building up the missing aluminum with Pyro-putty 1000, a 2 part aluminum filled high temp epoxy. It cures at room temp, but for full strength, it required baking at 180. They have others that don't require that. I also drilled in tiny pins into the good aluminum sticking out to give some lateral support, but that was unique to my situation. I lightly screwed in the cap after applying the epoxy so that it fromed to the cap, which had some distortion.

https://www.aremco.com/ceramic-metallic-pastes/

I also couldn't source gaskets, so I used permatex form-a-gasket. The aluminum fix is holding up, and it's been 6 years. However I don't think I waited long enough to torque the caps after using the gasket maker and have a very slight leak. You can't actually see it leak though. I also think I have raw water and coolant mixing a tiny bit to. The thing it's such a pain in the ass to get out, that I just purchased a new HX. If I'm pulling it out again, I'm going to just replace it for peace of mind.


Edit - forgot to add, you can get it from McMaster, but it's not under the brand name.
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Old 01-05-2020, 13:31   #13
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Re: Sealant for heat exchanger

Thanks for the replies everyone.
There is no way to replace the exchanger it hasn't been in production since I purchased the boat which is also how long its been leaking.
When I redid the engine about 8 years ago I had a shop rebuild it with epoxy and sort out sourcing the gaskets. Sadly that shop is no longer in business so I can't ask what they used. It worked for about 6 years until I was forced to run the engine with no raw water cooling and it seriously overheated.

Another problem is that now the boat is at the end of the world with no shops in site so I will need to take all the product down with me and attempt the repair myself.

I've considered using some sort of epoxy and the Permatex RTV gasket product (both of which I have on board) but I can't find any info on what pressure the RTV gasket will withstand. A threaded thermostat is one thing but this is something different.

As others have said... Im not too worried about temperature, its the pressure thats the problem. Does anyone know what pressures I can expect? I assume the coolant cap has some a relief valve built in but I can't find specs on it.

It's good to hear people have had success doing this themselves.
Thanks
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Old 01-05-2020, 13:46   #14
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Re: Sealant for heat exchanger

Quote:
Originally Posted by skipmac View Post
DO NOT buy Metalset from the only seller I found on Amazon. $57 for an 11 oz set. At least they offered free shipping.

Found it online from several aircraft supply companies for under $20 but shipping wasn't free. I finally ordered it from skygeek.com which came out to about $20 with shipping and FL sales tax. Never dealt with the company before so hopefully the order actually shows up. Will report back when it arrives.
I tried to find data to support the claim that it is way better than JB weld but cant find that... JB Weld has a higher tensile strength (3,960 psi vs 3,600 psi) and while JB Weld specs say temperatures up to 550F, MetalSet does not specify that, but in test data shows at 275F tensile strength reduced to 800psi.

For now, Im not convinced of any product outperforming regular JB Weld in this kind if applications.
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Old 01-05-2020, 13:51   #15
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Re: Sealant for heat exchanger

DON'T use JB Weld. Been there tried that. The JB became soft and pliable leaking within 15 minutes of running the engine. I used it on a cracked fitting on top of a coolant tank. Evidently it doesn't like heat. Maybe just filling some pits it would work...?

If you can get it apart, a slightly oversize (ie: thicker) Oring may work. It will depend on how badly pitted the bore is. But I have used rubber orings to 5000 psi water successfully in industry. How high you can go is all about how tight the gap is between the piston and the bore.
But at Heat x pressures, you ought to be able to make that oversize seal work well.
Also, get some Lanolin and coat your seals/orings with that. The stuff is amazing for high pressure water applications. Although if hot, it may not be the answer.
For sealant if it's really necessary Silicone sealant should work, it's good to 350-450 degrees, soft and will extrude to fill gaps.
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