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"Low Coolant" light

I have a 1996 Pontiac Transport with 45,000 miles. The “low coolant” light is coming on and the car is running hot. I have had the sensor changed twice. No leaks, the radiator is full and so is the overflow tank. Fan comes on to cool the radiator, water is swirling in the radiator also. What else can I check???

Have your car checked for a blown head gasket…Many shops have a “sniffer” that detects combustion gasses in the radiator…

I am not familiar with the design of the external reservoir in your car, but if it is lower than the top of the radiator, then I suspect that possibly it has plastic crumbling inside it. The resulting leak prevents the water from properly filling the radiator when the car cools, so the radiator is not completely full, and it causes the water to move around in the reservoir, disturbing the float on the water level sensor and lighting your low water level light. The age of your car is the clue - it is just about due for a new reservoir.

There is something else you can check… the actual temperature.

Get a 20 dollar cheapo IR thermometer and shoot it at the thermostat housing. Tell us what temperature it reads.

Would there not be leaks anywhere? I had a mechanic look at the car both cold and hot, and that was the thing he mentioned. There are no leaks anywhere…if that applies.

Open the radiator first thing in the morning when it’s stone cold. Is it full then??

Will do, thank you!