I have 2004 Saturn L300. The low coolant level light comes on when the temp reaches 3/8 of the gauge as the car is driven it reaches half of the gauge range, but does over heat.The coolant level isn't low. Is this a problem with the level sensor, water pump, or??? I've checked the temp between bottom hose and the top hose going into the radiator. When the car is first started the bottom hose gets hot then a few minutes later the top hose gets hot and the temperature between the two remains the same after that. Also opened the value at the bottom of radiator drained a small amount of coolant from the pressurized system. The level in the reservoir did drop, if i squeeze the bottom or top hose fluid does move around in the reservoir.

The gauges are analog I don't know what the actual operating temperature should be. The car was leaking a small about of coolant and a small amount of oil. For the past couple of months every week I've been driving back and forth to Miami which is about 200 miles. You could say the car is driven about 500 miles a week. Since I've been doing this the leaks seem to have stopped but now the low level coolant light is coming on. What else is the low level coolant sensor capable of monitoring?

It would be nice to properly diagnose the problem before taking it to a shop for repairs to prevent unnecessary work. Got any suggestions?
Thanks for you help

 

The coolant needs to be at or above the seam in the tank. Anything lower than the seam will turn on the light. It strictly monitors level. The sensors also fail and you have to purchase a complete tank to get the new sensor.

 

I have the same problem. I replaced the coolant tank and in the process found the wiring was damaged due to rubbing just below the tank. I repaired the damage and retaped the wiring. So far it works. Old tank had a ton of minerals built up and was due. I have a 2004 L300.

If other issues start though, it might also be damage to the BCM. It looks like the wiring issue may have damaged the motherboard in my case.