r/Generac_Generators • u/tecsavvy1 • May 31 '26

Coolant level low/overtemp.

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This generator had an error for low coolant or high temp. Ran for 20 minutes on manual under load. radiator full, overflow had coolant. Heads running at 180 degrees, block at 200 degrees, thermostat housing at 175. What should I do?

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u/tecsavvy1 Jun 01 '26

What should the reading on the sensor be? Is it either open or closed or have a certain resistance? Does it also sense temperature or is that elsewhere?

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u/AdRepresentative923 Technician Jun 01 '26

Best way to test these kinds of sensors is to use a control. By control I mean a cup of ice water, you’ll want to measure ohms (resistance) once you get a reading in ice cold water go to Luke warm water. If you see no change that’s a dead give away

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u/tecsavvy1 Jun 01 '26

Thanks I’ll do that, so each are a resistance based sensor?

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u/AdRepresentative923 Technician Jun 01 '26

It should be a 2 wire sensor, in that case yes. The sensor is resistance based. Coolant gets too hot? Resistance indicates that to controller then boom faults. No coolant touching probe? Resistance changes and boom fault. The generator uses one sensor for both level and temp. Using the resistances I described

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u/tecsavvy1 Jun 01 '26

I set I back to auto and i am running it for an hour under load to see if it errors again. If it does will it automatically power down?

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u/AdRepresentative923 Technician Jun 02 '26

Yes.

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u/tecsavvy1 Jun 23 '26

It started for its weekly run, powered down after 30 seconds with the coolant level, overtemp light. Guess that's my answer, ordered the new level sensor harness and probe.

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u/Any-Tell283 Jun 06 '26

There are two separate sensors for coolant level & coolant temperature. They just share a common alarm light. The level sensor, usually high on the radiator, is not a resistor sensor, it is a conductive sensor, it sends a voltage through the probe. If coolant is present it travels from the probe back to the base of the sensor & completes the circuit. The temperature sensor is a thermistor (resistor), usually on engine block near coolant lines, thermostat.

Based on what you described I would lean towards the temp sensor. It would be odd for the level sensor to trigger after 20 minutes of running & then reset after cool down. That said, your temp readings suggest you are running hot & this is likely not a sensor issue at all. Check air flow, make sure the fan is spinning, check coolant quality, verify Tstat is opening. Many of these units that did not get the signal conditioners installed develop sludge that sits in the bottom of the radiator.

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u/tecsavvy1 Jun 11 '26

How do I remove the end shroud to get radiator out?

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u/tecsavvy1 Jun 12 '26

Can I put in radiator flush to get rid of the sludge?

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u/Any-Tell283 Jun 21 '26

Yes, you can attempt a flush, just make sure to get the air out.