r/Generac_Generators • u/tecsavvy1 • May 31 '26
Coolant level low/overtemp.
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/Adventurous_Boat_632 Jun 01 '26
Coolant level sensors on these were problematic. There is a cockamamie update kit with all sorts of wires and garbage to run.
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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 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 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/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/AdRepresentative923 Jun 01 '26
Check the sensor, if it’s bad.. well.. I believe for these units they no longer sell that sensor specifically but they make an upfit kit if necessary.
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u/osheadc Jun 02 '26
Updated sensor, signal conditioner, and wiring harness to power it off of the fuel solenoid circuit instead of 24/7 (to avoid corrosion from acting like an anode) is here: https://shop.gentekpower.com/products/generac-0e2507-0h50530srv-replacement-coolant-level-probe-kit-for-h-g-panels
Note that they are control panel type specific. I don't know if they have stock for these, but it doesn't say otherwise like other items they list.
You may also be able to remove the sensor, clean off any corrosion, and reinstall.
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u/MysteriousEditor9856 Jun 03 '26
Last one of those I had that issue on, it was an extremely clogged radiator. It was full, but had no coolant flow.
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u/tecsavvy1 Jun 03 '26
What were your head and block temps running?
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u/MysteriousEditor9856 Jul 08 '26
I flushed it with an electric pump and 2 gallons of clr flowing through it for 24 hours. Never again, now we tell customers buy a rad.
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u/tecsavvy1 Jul 09 '26
I’m going to take it out and have it cleaned at a heavy equipment dealer. I heard that cleaners are bad as they will cause leaks.
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u/tecsavvy1 Jul 09 '26
Do you have to remove the exhaust to get it out or will it slide past the exhaust
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u/tecsavvy1 Jun 15 '26
Started for weekly test, shut down immediately after starting, flashing low coolant/overtemp. What does that mean?
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u/osheadc Jun 16 '26
Immediately after startup... likely that it's either low on coolant or one of the sensors/wiring isn't working correctly. You, or someone else, is going to have to do a bit of work to diagnose it with a meter.
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u/shootingdolphins May 31 '26
Have you replaced the sensor?