I have an O'day 31 with a Universal M18 engine that I've owned for several years. This year, I replaced the Raritan water heater with a Force 10 water heater, both water heaters have a heat exchanger that uses the engine as well as shore power to heat the water. I finished the work and tested it last week at the dock with no problems, but took it out on the water yesterday and after about 5-10 minutes under power at about 2000 rpms, the engine overheated. When I got back to the dock, I thought I may have hooked up the heat exchanger in reverse (not so, it was correct) and disconnected the return line and no antifreeze came out, leading me to conclude that the coolant is not being pumped through the engine, resulting in the overheating. I tried the air release valve on the engine (with engine on/cool; engine on/warm and engine off/warm) and got no air releasing. Does this sound like the coolant circulating pump? Any help would be greatly appreciated. Also, if anybody knows of a competent marine diesel mechanic in the Quincy, MA area, I would very much appreciate a name/number. Thanks! Jim Malloy "LegaSea" Quincy, MA
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Air Lock in Coolant lines to Water Heater?
Jim, My guess is that you have some air in the lines that circulate the hot coolant to the water heater from the heat exchanger. Often there is a petcock installed in the highest line, just as it enters the water heater. By cracking that open and letting any air bleed off, closing it when the coolant starts to come out, should take care of the air lock and overheating problem. I had this identical problem when I replaceded the coolant lines, and it took awhile to get to this solution. (Not sure why no coolant came out when you disconnected the return, but if the pump was working before you replaced the WH, I would try the air lock solution first.) Hope this helps. Ed Ryan
Jim, My guess is that you have some air in the lines that circulate the hot coolant to the water heater from the heat exchanger. Often there is a petcock installed in the highest line, just as it enters the water heater. By cracking that open and letting any air bleed off, closing it when the coolant starts to come out, should take care of the air lock and overheating problem. I had this identical problem when I replaceded the coolant lines, and it took awhile to get to this solution. (Not sure why no coolant came out when you disconnected the return, but if the pump was working before you replaced the WH, I would try the air lock solution first.) Hope this helps. Ed Ryan
from the owners manual
Fresh Water Circulation Diagram All Models Except M-15 Normal Range 165 to 195° F Fresh Water: 1. Coolant (fresh water with antifreeze) is introduced into the system from the coolant section of exhaust manifold by removing pressure cap and filling manifold tank within one inch of lower rim of fill port. 2. Fresh water engine driven circulating pump moves coolant from heat exchanger through engine block circulating pump and thermostat back through exhaust manifold into heat exchanger to be cooled. The manifold serves as the engine expansion tank to allow for expansion of coolant as it is heated. You also fill the system at this point. In some cases when hot water heaters are installed an expansion or surge tank may be required to prevent air from entering the system. Should your engine overheat, first check coolant level to make sure it is not low which would cause air locks to develop. If air does enter the system, it may require a couple of fillings to remove the air pocket. A momentary increase of engine RPM to approximately 2800 to 3000 RPM may aid in moving the air from the system. In some cases it may require doing this 2 or 3 times. Do this just as you notice the temperature starting to rise above normal.
Fresh Water Circulation Diagram All Models Except M-15 Normal Range 165 to 195° F Fresh Water: 1. Coolant (fresh water with antifreeze) is introduced into the system from the coolant section of exhaust manifold by removing pressure cap and filling manifold tank within one inch of lower rim of fill port. 2. Fresh water engine driven circulating pump moves coolant from heat exchanger through engine block circulating pump and thermostat back through exhaust manifold into heat exchanger to be cooled. The manifold serves as the engine expansion tank to allow for expansion of coolant as it is heated. You also fill the system at this point. In some cases when hot water heaters are installed an expansion or surge tank may be required to prevent air from entering the system. Should your engine overheat, first check coolant level to make sure it is not low which would cause air locks to develop. If air does enter the system, it may require a couple of fillings to remove the air pocket. A momentary increase of engine RPM to approximately 2800 to 3000 RPM may aid in moving the air from the system. In some cases it may require doing this 2 or 3 times. Do this just as you notice the temperature starting to rise above normal.
Try expansion tank
I had same problem with O'day 30 and corrected with installation of an expansion tank.
I had same problem with O'day 30 and corrected with installation of an expansion tank.
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