Bad Heat Exchanger???

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MichaelNJ

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My port engine (Mercruiser 6.2 Horizon FWC) started to overheat today. I checked my Seawater pressure and it was fine. Checked my strainer and it was clean and water was flowing through the seacock. I opened the pressure cap on my heat exchanger and didn't see any coolant in there. Recovery tank was empty too. Looked around the bilge, didn't see any coolant anywhere. Hoses all looked good. Put a half gallon of coolant into the heat exchanger and started to engine. The temp started creeping up again.

I took off one of the end caps to see if I needed to flush the raw water side coolant poured out. So it looks like there is a leak between the raw water and fresh water passages. That surprises me. I believe it's copper so I wouldn't expect it to rot out.

Is this common? Just a matter of changing the heat exchanger which shouldn't be too hard.
 
Get it pressure tested before you replace it. The are other ways to loose the coolant.
 
I'm going to take it off and bring it to a radiator shop. I'm also going to take the end cap off again and fill it again and see if the coolant is coming through one of the tubes. I understand you can have a bad tube plugged at each end. But for $1,800, you're right. I'm not going to just replace it.
 
Pressure test. The fluid is under pressure went it comes into it, a crack might not leak without pressure.
 
Not uncommon for the tubes in the FWC to leak. Raw water runs thru the tubes. Pressure test the coolant side. You don't need much pressure. Wrap a wet rag around a air hose and pressure test the 3/4" tube in the middle of the top section. look for leaks from the end cap side. might need a flash light. If you see or locate a leak, it's easy to fix. The tubes are 1'4" brass. You can buy 1/4" brass rods at hardware store. You're trying to plug up the brass tube. Rough up the end of the tube and rod and clean real good. You can solder OR JB weld the rod and tube. let set at least 24 hrs. You might be able to plug both ends without a brass rod by just plugging the ends of the tube with JB weld.

Let us know if that was the problem. If not, the problem may internal...which will get a bit more expensive unless you can pull the heads yourself.
 
Also likely a good time to review who and how the zincs are being serviced on those heat X-changers.
 
Thanks Jim. I was thinking JB weld would be an easy fix.

Smitty, Mercruiser doesn't use zincs in the exchanger or any part of the engine.
 
Sure they do. On standard San Juan exchanger, the zinc fits in a plug...usually on the raw water tank, lower fill side. Not sure what type drive system you have, that's why I said fill side as radiator cap is on the right of middle.

Also on ex manifolds/risers and blocks, in place of drain plugs
 
No zincs in heat exchanger or the oil cooler?????? Don't think I've ever seen that.
 
I agree that there should be but not on my engine. I just replaced a the transmission and oil cooler on my other engine and there is no anode in the oil cooler either. The aftermarket exchanger made by Seakamp uses a pencil zinc in the drain plug.
 
If the X-changer has no zinc then it must use a method to isolate it from other metals in the system to prevent corrosion. With trans coolers and oil coolers you can select CuNi coolers without zincs and set them on a replacement schedule of 7-9 seasons or so with great results.
Raw water heat X-changers in salt water with no isolation and no zincs will last about the same amount of time.
I see your boat is an 06' so any salt water cooled items will be due - trans cooler, fuel cooler, oil cooler and heat exchangers on the mains on the genset unless completely isolated or zinc protected.
 
My Kohler 7.3 has a pencil zinc in the heat exchanger that I replace every year.
 
"My Kohler 7.3 has a pencil zinc in the heat exchanger that I replace every year."

As long as your zinc is less than 60-70% gone when you replace it then that heat x-changer will last a long time.
Usually these heat exchangers and coolers are made with similar materials with similar thickness and methods.
Yes you can find straight copper coolers vs the more robust CuNi coolers but for the most part they are mostly all the same from any reputable supplier.
 
quote:
Originally posted by Gregory S

No zincs in heat exchanger or the oil cooler?????? Don't think I've ever seen that.

Click to expand...


MTU is one engine maker that I can think of off the top of my head that uses no zincs.
 
"MTU is one engine maker that I can think of off the top of my head that uses no zincs."

I have owned 4 boats (8 main engines) that utilized Hino (US marine) diesels which do not utlize zincs either. Between those that I owned and a number of other Hino's I have worked on the system of isolating any dissimilar metals in the heat x-changer works great as long as they remain isolated. The ability to check for that isolation is simple and quick but I do not think it is applicable to these 6.2 Horizons.
 
Is it just a matter of putting an ohm meter between metal on the raw water side if the exchanger and the engine? It really doesn't matter I guess. I know I have a leak so do I need to replace the entire exchanger (and the one on the other engine) or can it be repaired. I called an auto radiator shop and he didn't want to do it.
 
Michael - It does sound likely the H.Ex. is leaking. Have you been checking the pencil anode once a month and replacing it any time it looks 1/2 gone ( remaining part will be very porous)? That is critical to longevity. Also , you might make sure the ground/bonding connection is intact.

Even though most H.Ex.s are likley copper, that is the cheaper alternative to the much more corrosion-resistant cupro-nickel ones. Not sure but I suspect the latter is what Crusader uses as OEM. But the pencil anode replacements are still critical what ever material yours may be made of, particularly used in SW.

If you google marine heat exchanger repair, there are shops that specialize in that , and they make or sell new ones too. I've always just bought new ones presumably for best long term results.
 
Michael posted - "Mercruiser doesn't use zincs in the exchanger or any part of the engine"
 
"I took off one of the end caps to see if I needed to flush the raw water side coolant poured out. So it looks like there is a leak between the raw water and fresh water passages. That surprises me. I believe it's copper so I wouldn't expect it to rot out."

Well you found your problem... Bad heat exchanger, replace it and enjoy the rest of your boating season...

If you have coolant in the raw water side, it's leaking. You think copper doesn't corrode in sea water?? You got to be kidding, right? Copper will rot out, this is why you never use copper fittings in a raw water circuit Like air con. This is why most manufacturers use zincs.
 
I tried to tell you how to locate and repair a leak. They're all brass/copper which will readily solder. If you want to spend the $1500 rather than $5 for solder...
 
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