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7.4 mercruiser 1998. indicates overheat with alarm

D

Dan16

New member
Temp gauge shows 200+. Lazer temp at thermostat is 160.
Alarm going off. Have replaced pump, impeller, thermostat, manifolds and raisers. Back flushed system. Replaced gauge, and sending units. Good water flow out. Happens at idle or up on plane. Need ideas!
 
having a poor ground will cause the gauge to read incorrectly. Try running a temp ground from the neg battery to the neg buss under the dash.
the alarm goes off from no oil pressure, high engine temp and low/no outdrive oil
 
Bt Doctur said:
having a poor ground will cause the gauge to read incorrectly. Try running a temp ground from the neg battery to the neg buss under the dash.
the alarm goes off from no oil pressure, high engine temp and low/no outdrive oil
Click to expand...

Many other ideas.
That didn't work.
Could engine control mod cause it?
 
[FONT=&quot]I had a similar problem that indicated high temperature and triggered the alarm and a marked reduction in power. When queried, the Mercruiser tech’s first question was “is the temp sensor operational?”. Trouble shooting proved that the engine was NOT overheating and the high temperature reading/power reduction was due to the sensor/transmitter (or its circuit). The fault was ultimately solved by introducing resistance into the temperature sensor circuit to bring the indicated temperature to the correct level. What I thought was a troubleshooting technique was actually the recommended permanent repair. Hope this is helpful.[/FONT]
 
adding resistance to the sender circuit isn't a fix, except for one temp...the sender uses a thermistor....

As pointed out in post #2 and reiterated in post #4, there's more than one switch that will activate the alarm....the data in the original post suggests its not the temperature switch driving the alarm and that the temp gauge sender unit is out of cal.....
 
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