TEMP ALARM RUNS HOT & COLD

[MooreBoys]

2004 OPTIMAX 115hp on 20x72 Express Aluminum Boat with center console, SmartCraft, only 50hrs tunning time on this new rig.<br />PROBLEM: Sometimes at part throttle on trim the Engine Overheat Alarm sounds. I them switch from RPM Mode to Temp Mode finding a reading of less that 160 Degrees. Reducing the rpm will put out the alarm. Continuing to operate the engine at 3800 Rpm the Temp Gage starts dropping and bottoms out at 112 degrees. My dealer has no experience with optimax units. Mine was the first he had sold. He caters to smaller classic engines. While this is going on there is a good strong stream of water leaving the engine. This problem is intermittentbut is of great concern to me. This unit has a thermostat. I watch the temp gage upon starting out. The temp is in the 70/80degree range. The engine operated slowley and carefully shows the temp to climb to 160 degrees ang when the thermostat opend the temp drops to 140 degrees (this is where it normally operates. I cant figure hot why tat times the overheat alarm sounds and then very shortly after the temp just keeps droping to the 110/112<br />degree range. I dont think the engine is running hot or cold....I think I have a sensor and or gage malfunction. Anyone got any ideas on this problem.<br />MooreBoys

 

[tryan]

Re: TEMP ALARM RUNS HOT & COLD

i was doing a little inspection on a four stroke yamaha. i removed the stat housing and started the motor. there was no water at the thermostat at idle. ( i am assuming the impeller is lacking a vane or two. )

 

[Oldsaltydog]

Re: TEMP ALARM RUNS HOT & COLD

It could be a malfunctioning thermostat. Or it could be a bad temp sending unit. To test the latter, take a pan of water, place it on a range burner, place the sending unit in there, along with a kitchen thermometer, and attach an ohm meter to the wires (above water). When current begins to flow, the thermometer should give you a reading and you could find out from a manual if the numbers match up. You can use the same pan for testing the thermostat, but you will not need the ohm meter. Just check visually at what temp the thermostat opens and if it does so consistantly -- again a repair manual should give you the specs. You could also possibly have some sort of an obstruction in the cooling system, perhaps at the thermostat housing.