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Old 10-06-2005, 11:33 AM
jdaly986 jdaly986 is offline
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Overheating problems

I have a 78 C&C 34 “Good old Boat” bought about four years ago. The old owner had just installed a “rebuilt”(new version) Atomic 4 that from all indications was done adequately, though probably not up to my standards. It is a “newer” model with a folding prop and a reduction gear. Crusing RPM is about 2000 and full power (WOT) at about 2500 to 2700 RPM. In any event, soon after I started using the boat I experienced chronic overheating problems. I did all the things the various sites and Don recommend: acid cleaning, new thermostat, new pump impeller, thicker cam shoe, bypass restriction, new thermostat housing etc. The most effective help was the Moyer flushing kit, procedure and acid cleaning. This seemed to help for about 2-3 months on the water after a flush (I use the boat weekly with about 2 hours on the engine), then it would become overheating prone again and unreliable. I found it notable that a large amount of black “silt” was discharged in each flushing operation.
I noticed during overheating incidents widely uneven temperatures in the engine and steam noises from the block. I also noticed decreased water flow from the exhaust which I surmised might be because of a steam “bubble” forming in the engine cooling passages and higher head pressure on the pump.
This seemed to occur even at 180 F measured at the temp sender location. Also, once temperature reached 180F +, thermal runaway would occur rapidly and the engine would over heat because of steam formation internally. I found I could not run the engine under load at more than 170F or it would overheat rapidly.
Eventually, I removed the side plate to perform the modification to the water injection cap Don recommends, drilling a ¼ inch hole in the top of the cap. While I had it open I was amazed at the amount of “mud” in the cooling passages. After cleaning the water jacket area, and flushing the block, the engine ran fine until a month or so later when it gradually started to overheat again.
At this point I was really dissatisfied with the engine, and contemplating a 10K investment to re-power with a new diesel in order to get some reliable power. Then I remembered overheating problems I had in an old Fiat I once owned, traced to air in the closed loop cooling system that would allow steam pockets to form in the engine restricting coolant flow. I reasoned that my problem was a combination of:
a) Fine slit from the Chesapeake Bay river bottom where I operate my boat, being sucked up into the pump, through the filter and settling in the engine block over time (like a centrifugal filter) while I pumped the clean water overboard! This caused a gradual buildup of “mud” in the engine and reduced cooling flow/heat transfer area. By the way, the river bottom here is always about 3-4 feet below my intake, but I guess the movement of the boat stirs up the sediments, or they are naturally suspended).
b) Insufficient cooling water flow through the engine unless it is very close to perfectly clean. This may be due to the size of my intake thru hull (about ½ inch diameter from the boat builder) the size of the cooling pump (though I have replaced it with the larger cam shoe and new impellers etc.) or just restrictions in the engine block.
In desperation, I bought the Moyer Marine fresh water cooling system. I thought at the very least it would:
a) Allow the engine to run hotter than 160 F by eliminating air in the system and the ability to form steam “bubbles” internally. Also, antifreeze and a system pressure would raise the boiling point.
b) By running the river water through a heat exchanger, and not the engine, silt would not build up in the engine but in the heat exchanger if at all, reducing the need to flush so often.
My only concern in installing the system was if some scale got loose in the engine/manifold and plugged the heat exchanger, so I added a strainer to the coolant return loop.
The results have been excellent. I find I can run the engine wide open without overheating if required for an extended time as I had to this summer when an intense squall hit with sustained 50+ kt winds in the Magothy (this off a lee shore; Gibson Island) . I had to claw off and ran the engine wide open for about 30-45 minutes to keep from running aground. Under normal cruising speed it always runs fine and about 160-180 F. I have no more anxiety about if I will have to shut it down at an inopportune moment to cool off. The cooling system and other Moyer engine upgrades (electronic ignition, new coil, new adjustable carburetor) have turned it into reliable, and economical auxiliary power using about 1 gal per hour at cruising speed. I ran it for two months with fresh water in the cooling loop and found nothing in the strainer. I flushed the heat exchanger and it was clean. I think the heat exchanger has high flow velocities in it in all areas, and not significant low flow areas, so the sediment does not centrifugally settle out in it, like it did in the engine block. The system now has propolylene glycol coolant in it, and the engine temperatures are much more even and there are no “hot spots”.
As a mechanical engineer, I knew that theoretically a closed loop, air excluded, and pressurized cooling system is more efficient, will allow higher operating temperatures, is better for the engine by keeping temperatures equalized, reduces corrosion, and eliminates the possibility of introducing sediment into the engine which acts like a big dirt trap. But, you never know how much of a difference something like that will make in a real case, especially in an engine that was designed to be robust enough to accommodate open loop cooling. It is also a question if the heat exchanger in the kit is sized large enough, etc. However Don, I thought you had done the homework and it would work properly, and at worst I would still have reduced overheating problems for other reasons.
Well, tt was the best $400.00 I have spent on this boat! I now have a reliable engine and my overheating problem is solved. My boat has an internal thermostat and it works fine with this setup. One modification I made that works well is a bypass on the engine coolant side of the heat exchanger, to allow faster warm-ups when the water temperature is low.
I would strongly urge anyone having similar problems, especially operating in shallow Chesapeake creeks and rivers to consider the Moyer freshwater cooling modification if for nothing else than to keep your A4 from being the bottom filter for your creek!
John Daly

Last edited by jdaly986; 10-06-2005 at 11:43 AM.
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Old 01-16-2008, 11:32 AM
castinemarine castinemarine is offline
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Another Good Old C+C 34

I bought an old 72' Mk I around the same time you did.
The problem you addressed above probably saved me from the 10K engine retrofit you talked about. I'd like to hear anything more you might have to say about your experience!

Thanks! Chris

72' C+C 35 Mk I "Surfrider"
South Freeport, ME

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