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Diagnosing bad heat exchanger

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steve hale

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"On my crusader 5.7 300hp powe

"On my crusader 5.7 300hp powerpack repowers, My port engine runs 30 deg hotter than starboard and climbs slowly over 3600 rpms. When we did the repower, we kept the heat exchangers and changed everything else. The old engines did the same thing. The flow from the raw pump is great, the sea strainers are clean. I can smell some antifreeze at the stern in the exhaust on the hotter engine. I'm assuming the heat exchanger is leaking slowly into the exhaust, since I will have to add antifreeze regularly to the hotter engine. It is not going over 200, so I don't think it is going out of the overflow. I do not think the heat exchangers have been cleaned in the repower. My question is this. Can I swap heat exchangers, and see if the higher temp follows the heat exchanger there by isolating my problem. Or are the ports different for LH or RH rotation motors. If it is leaking antifreeze, Am I putting the good motor at risk by swapping them? I know I could take them to a radiator shop and pressure test them, but I'm not in a metro area, and It might be a little harder than you think.
Steve"
 
"Steve:

Do yourself a huge

"Steve:

Do yourself a huge favor and replace that one exchanger. If that's the problem, fine--all fixed. If not, you have one of them replaced, right?

Jeff

PS: Are you absolutely certain there is no air leak in the system before the raw water pump? THe tiniest air leak will screw things up big time, especially while on plane."
 
Pressure test the exchangers y

Pressure test the exchangers yourself. Screw a tee fitting into one of the drain plugs and attach a pressure gauge that will read accurately down to 10 psi and a hand pump to pump up to 6 psi and see if it will leak down. If it does then block off the input and outputs on the heat exchanger and retest to localize the leakage.
 
"Good, but that won't dete

"Good, but that won't determine if there's a bunch of crud in there that's blocking water flow. you need to pull the covers off and go through it.

Jeff"
 
fastjeff said:
"Steve:

Do yourself a huge

"Steve:

Do yourself a huge favor and replace that one exchanger. If that's the problem, fine--all fixed. If not, you have one of them replaced, right?

Jeff

PS: Are you absolutely certain there is no air leak in the system before the raw water pump? THe tiniest air leak will screw things up big time, especially while on plane."
Click to expand...
 
Hi Jeff, I have a similar problem to what Steve describes…how do I diagnose an air leak on the intake side of the circulation pump? Thanks, Dave
 
Usually better off starting a new thread than to start with one over a decade old....

air leaks on the suction side of the circulating pump aren't common...if the leak is in the pump itself, not sure how you could prove it...once the engine warms up, the heat exchanger should show a pressure increase....

which engines do you have and what are they experiencing?
 
steve hale said:
"On my crusader 5.7 300hp powe

"On my crusader 5.7 300hp powerpack repowers, My port engine runs 30 deg hotter than starboard and climbs slowly over 3600 rpms. When we did the repower, we kept the heat exchangers and changed everything else. The old engines did the same thing. The flow from the raw pump is great, the sea strainers are clean. I can smell some antifreeze at the stern in the exhaust on the hotter engine. I'm assuming the heat exchanger is leaking slowly into the exhaust, since I will have to add antifreeze regularly to the hotter engine. It is not going over 200, so I don't think it is going out of the overflow. I do not think the heat exchangers have been cleaned in the repower. My question is this. Can I swap heat exchangers, and see if the higher temp follows the heat exchanger there by isolating my problem. Or are the ports different for LH or RH rotation motors. If it is leaking antifreeze, Am I putting the good motor at risk by swapping them? I know I could take them to a radiator shop and pressure test them, but I'm not in a metro area, and It might be a little harder than you think.
Steve"
Click to expand...
Hi All,
I'm commenting here since coolant leaks can be very frustrating (as we can see from the various posts). I'm not a mechanic but will tell you what we found on our Mercruiser 5.7L (1989 Carver). The temp would stay within range as long as we were cruising at around 1,750 RPM. When we would back down the RPM to about 1,000...coming into dock or whatnot, the engine would overheat and we were losing coolant. We chased this problem around for a couple years. We think we finally have it fixed. In the riser elbow, there is a gasket, then a thin metal plate, then another gasket. One of the gaskets had begun to fail. The thought is that when the engine was at higher RPM, there was 'equal' pressure between the seawater side of the gasket area and the coolant side of the gasket area. When the engine was hot, then RPM reduced, the pressure was higher on the coolant side of the gasket area, hence, then spraying coolant into the seawater exhaust side of the gasket and then out the exahust with the seawater. We replaced the riser elbow gaskets and it appears to have fixed it. I've had 2 sea-trials so far. It was difficult to inspect the gaskets after disassembly since they get a bit torn up in the removal process. What we did see was some evidence of 'rust' in the gasket area where there probably shouldn't have been any....and if you looked down the riser, the top couple inches of the riser area was 'clean' of exhaust carbon. The theory was that if there was a leak, that may have acted like a 'steam cleaner' and cleaned our the carbon of the inside top area of the riser (top 2 inches or so). The riser without the leak had more carbon on the walls of the riser than the leaky one....they looked different.

I hope this post helps somebody with a similar problem...
 
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