Temp showed high close to 200 but went down to 180 or so and alarm still sounding Any ideas where to start looking? I will replace the impeller and thermostat as I'm concerned about the temp getting too close to 200 degrees.
Thanks in advance for your ideas.
Howdy,
That alarm system on your 7.4 engine is a rather simple circuit. 2 wires go to your alarm buzzer. 12v DC power and a ground connection. The "Ground" connection is actually the "signal wire" connected to oil, temp, and drive lube sensors.
Any time the key is on, 12vDC is provided to the buzzer.......... Since the oil pressure is zero (before starting) the buzzer should sound. (testing the buzzer every time)
"Sensors" back in the engine compartment include an oil pressure, temp and drive lube monitor switches.
Those switches are connected to ground and the "sensor" wire such that when any ONE (or more) of them closes, it completes the circuit to ground to sound the alarm.
Once the engine produces sufficient oil pressure to open the switch, the buzzer will stop (since the temp is cool and presumably, the drive lube monitor is full)
Understand that ANY "completion" of the circuit to ground will activate the buzzer.
You can check this by getting a wire and holding one side to any ground point (block etc) and touching the other end to the temp, oil pressure or drive lube monitor switch. (the drive lube monitor switch connections are not usually exposed but the oil pressure and temp usually are)
Also if the sensor wire that goes from the engine to the instrument panel (buzzer) is frayed or exposed and touches any ground point, it will also activate the buzzer.
To isolate switches, with the alarm sounding, disconnect each one, one at a time. when you disconnect the one that is closed, the alarm will stop. If all three are disconnected and the alarm still sounds, the wire is frayed and is touching a ground some place between the engine and the buzzer.
If you're really reaching 200 degrees (open or closed cooling?) It's possible that the engine is REALLY getting too hot.
Change your raw water impeller and if it's disintegrated, you'll need to remove and clear all the debris out of your oil cooler because it's likely plugged.
AND I would check the oil cooler anyway for debris from previous failures. Mine was COMPLETELY plugged with impeller fragments from multiple raw water impeller failures from a previous owner.
Regards,
Rick
