Overheat Alarm

M

Mike H.

.
Mar 16, 2009
303
Hunter Vision-36 Richmond
We were out last weekend at Duxbury Reef doing some fishing when the overheat alarm came on.

We had been idling after trolling and motor sailing for a long time.

I shut the engine down, let her cool off and cleaned a little seaweed out of the raw water strainer.

I started it back up and the alarm sounded again, but with increased RPMs, the alarm quit. The engine ran cool with no problems on our motor home.

What do you think caused it to overheat? The low rpms for a long time? The sea weed in the strainer? Could the elbow be corroding shut again? (I boiled it out with acid once before). Or do I need new coolant? A loose belt?

What do you all think?

It's a 94 Yanmar 3jh2e.
 
Navicula

Navicula

.
Dec 14, 2011
316
Navicula 430 Hunter Toronto
check the impeller for broken fins.. it may not be getting enough water at low rpm.........another good alarm is a aqua alarm...it sounds when there is not enough water going through ( it usally set up to sound before the engine get to hot), I also carry a lazer temperature gun and I check the temp of the block to make sure that the gauge is matching what the gun says.....its called the processes of elimination.

sounds like an impeller to me:)
 
B

Benny17441

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May 24, 2004
7,190
CC 30 South Florida
I would bet the seaweed in the strainer restricted flow which was inadequate to maintain normal operating temperature. The alarm buzzer will go off well before a damaging temperature is attained. Our buzzer one time went off as we were approaching an inlet in New Jersey just as it was turning dark on us. We had a temperature gauge and observed that although the temperature was elevated it had settled and stopped climbing. We deduced that we had partial water flow and continued motoring for another 1/2 hour while watching the temperature gauge. having to listen to the darn buzzer was the worst of it and at one point even considered removing the panel to disconnect it. Next morning we removed the intake hose and determined that the small amount of water coming up the valve pointed to some blockage. We hooked up a compressed air tank and sent down a blast and instantly proper water flow returned. We later found a plastic ice bag floating in the proximity of our stern. We inspected the impeller which was fine and checked the oil viscosity which showed no significant breakdown and we were ready to go. Not having the gauge or having failed to interpret its reading would have meant shutting down the engine and anchoring outside the inlet to try and diagnose the problem. Another thing that can overheat the engine is trying to power out of a soft grounding; applying full throttle when the boat isn't moving will heat it up at least to sound the buzzer. By increasing your RPM you forced more cool water through the exchanger to bring the temperature of the engine coolant down. If the engine is running cool again you are likely good to go, just remember to periodically clean the strainers.
 
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