I have a Mastervolt 6 Genset. Sits in a plastic, insulated case above the boat engine
. It has a Mastervolt exhaust
gas separator, a device which separates the exhaust
gases from the exhaust water
. The separator is downstream from the exhaust mixing elbow
. The gases are vented out the back of the boat through an opening in the transom, while the water
is discharged via a thru-hull under the boat. The purpose of this is quiet running, i.e., no above waterline water discharge to make noise
for the Genset is a two cylinder Mitsubishi diesel
. The engine overheats intermittently. The Genset is 2000 vintage with 258 hours on it. Sometimes it runs under load w/o any problems; sometimes it shuts down after running with a load for 45 minutes; sometimes it shuts down right after start-up. The discharge of the water under the boat makes it impossible to determine the cooling
water flow. The usual suspect is the impeller, but it is fine. All vanes and ribs intact; no missing pieces. I changed it last summer. Looked at it a week ago. The engine has two heat sensors, one for the coolant
and another for the exhaust discharge. There is also an oil
pressure sensor, and any of these three can shut down the engine. I think they all work—as well as the thermostat. I say that because I have run the engine w/o the thermostat, and it has over heated. I have had a heat gun on the engine, and when it does shut down, it has really overheated. Not a false alarm
. The coolant
temperature sensor is set to shut it down at 220-234F, and it does. Heat gun readings confirm it. One can also see air bubbles running from the coolant tank in a clear tube to the coolant expansion tank. Caused by boiling, I assume. Plenty of oil
. Plenty of water coming in via the intake seacock and strainer. The strainer is a clear Vetus model, and I can see the water flowing.
One theory is broken impeller pieces floating around in the cooling
jacket. I am contacting the boat’s former owner—I bought the boat last year and have not had much occasion to use the genset. Haven’t figured out how to get to them if it is broken pieces of impeller, and I’m not sure I can check for scale as the heat exchanger
is under the engine and generator
. I’d have to remove the Genset from its plastic container, which means the whole thing has to come out. And one would think that were the problem scale, it would always overheat--nothing intermittent.
suggested another theory. Both the intake and discharge seacocks are located next to each other on the bottom (hull). The mechanic
thought that if the gas-water separator were malfunctioning, it might be discharging bubbles (of air and gas) along with water under the boat and next to the intake opening. The bubbles get sucked in (intermittently owing to current
or in a marina) and air gets into the cooling system. I have to add, the one time I ran the generator
while underway (and with a full load on it), no issues. Ran it for two hours and was doing 6.5 knots.
Does this explanation (about the seacocks being too close) make any sense to anyone? Can always crank it up and get a diver to look and see if there are any bubbles.