Just last week, my check engine light went on. I pulled out my code reader, and plugged in-it read p0128 (coolant temperature too low). I checked everything, and the heater works fine.I bought a new thermostat, since i read that this code usually means a stuck-open thermostat. Next, today, the low coolant lamp lit up_ I checked the reservoir, and it was down a slight amount-I added about 5 ounces of coolant, and started the engine-both lights went out. I cannot detect any leaks, and there is no indication of any internal leaks-what could it be?
Is it still complaining of low coolant temp? The sensor itself may be failing. Unless you topped off the coolant the day before, I wouldn’t worry excessively about being down a half cup. Actually, on re-read, you probably had an air bubble in after putting the new thermostat in, and once it got “burped” you were down 5 ounces.
Otherwise, what kind of car is this?
It is a 2002 Saturn SL1, with 85,000 miles. The check engine light has gone out.
Sounds to me like a weird car un-problem. Drive on!