Universal m25 Heat Exchanger

[CruiserDave]

My wife and I are on our way down to the Bahamas and are in Charleston now. I just checked my engine fluids (yes, do it every other day) and changed the oil. Ther was no water in the oil and no oil in the water. When I checked the radiator on the fresh water system I had quite a suprise. Clear water. Tasted it and it's a bit salty. I believe I have a problem with my heat exchanger. Anyone have an opinion here. If it is the exchanger has anyone replaced their's before? Any advise? Any help will be appreciated.

David

 

[SailingCal21]

I've removed and replaced mine several times to clean it out, pencil zinc pieces, scale and the like. It's a pretty straightforward project. If your's is a 2" diameter one it would make sense to take the opportunity to upgrade it to a 3" one.

 

[Max15631]

I have the same heat exchanger on my 84 ODay 34, and Scott is correct in recommending installing the larger heat exchanger. Mine isn't leaking (I hope), but it starts to run pretty hot at higher rpm's. My understanding is that the 2" dia. is marginal, at best, for this engine, and Universal themselves issued a technical bulletin suggesting that owners with overheating problems upgrade to the larger diameter.

Max

 

[BarryL]

Hello,

As others have written, it's pretty easy to remove the Heat Exchange. There are four hoses and one or more clamps. You have great access from the quarter berth.

Make sure you close the raw water intake before you remove the HX. I removed mine and took it to a radiator shop. For $50 they pressure tested and then tank cleaned it. It came back looking like new.

I would flush the cooling system before you add fresh coolant. Also note that bleeding the air out can be a real pain.

Good luck,
Barry

 

[rajhnsn]

I've been thinking that I'd like to service my heat exchanger before there are problems with it. Sounds like a good idea to have it pressure tested. I've noticed a bit of corrosion starting to build up at the sides. Is this normal? The PO also profided a deticated zinc to the heat exchanger that I replaced two seasons ago. It is showing very little wear. The picture shows how the wire is clamped to it. I've read that it is a good idea to provide a dedicated zinc because the water that remains inside is isolated from the engine block and can lead to premature corrosion.

Is this the larger size?

 

[jibes138]

rajhnsn, not sure what you mean by a dedicated zinc. The heat exchanger has a pencil zinc that unscrews from the bottom port side of the heat exchanger. The owners manual says to check it monthly, it is in the raw water circuit of the heat exchanger. You can buy just the zinc part of the pencil and save a few bucks but they do typically dissolve pretty fast and unfortunately the debris can clog up the cooling passages leading to flow reduction of cooling water. The exchanger is a copper based material brazed together so what you are likely seeing is corrosion of the copper causing the green film through the paint. Copper turns green like that. You can remove it, clean it up and re-paint it if so predisposed. I am looking to upgrade mine to the 3 incher. I think yours is a 3 inch but hard to tell for sure, take a ruler and measure it if you want to be sure.

 

[rajhnsn]

Thanks for the heads up on the zink. I'll have to take a look at mine to see if it is worn away. The dedicated zink is attached to the hull of the boat. There is a grounding wire attached to the screw of the backing plate (small block of wood) which is attached to the heat exchanger.

 

[SailingCal21]

Perhaps the PO was trying to slow down the failure rate of the pencil zinc. I'll bet that it doesn't help much. I'm of the opinion that the pencil zinc in Karma erodes due to cavitation faster than being an anode. Whenever I pull mine it appears more eroded than corroded.

 

[Winters Dream]

David,

I hate to spend money for boat repairs because parts and labor are priced three times the outside world price.

Look around the heat exchanger to try and find the leak, which is probably internal so you won't find it.

Buy car radiator "stop leak" or some such name at an auto parts store. Follow the directions and pour the stop leak in your heat exchanger. Run the engine for the length of time on the directions. This should stop any leaks.

Fill the heat exchanger with some cheap, colored watery fluid, like strong KoolAid. Run the engine for awhile. If this new fluid doesn't change color or become clear, the problem should be fixed.

Don't forget to refill the heat exchanger with antifreeze before you sail your boat to a cold climate, if you're going there. It will freeze and possibly burst without it.

Bob Lendvay[/quote]

 

[Fogg]

David,

Bite the bullet and install (or have installed) a new 3" heat exchanger with all the proper gaskets and zinc. My Catalina 30 went from running at about 190 degrees with the 2" HX to a pretty constant 165 with the 3". I check the HX frequently during the summer and change it annually as part of spring commissioning. If you can get the screw in pencill zinc to fit your screw fitting, so much the better. Get several. Do remember to shut the intake thru hull before removing the zinc for examination. Just as important, remember to open the thru hull before you restart the engine.

Good luck and fair winds.