I have a 95 z28 that had the low coolant light come on. I replaced the coolant level sensor this morning and the light went away at first, then came back on, now it stays out after I’ve started it back up about 10 times now. I filled it back up with coolant and there are no visible leaks anywhere. I also had the radiator flushed and a new thermostat put in about a month ago. No issues until the little red light with the down arrow and squiggle came on. Now it heats up almost to the red zone when idling for a while or stuck at a traffic light. While driving it cools back down to less than the halfway mark and more typical operating temp. I unplugged all of the cooling fan relays and plugged them back in, but that did nothing. No fuses are burnt out or anything. It just started acting up after putting a new coolant level sensor (the little square with the metal clip that plugs into the radiator. Any ideas why it is doing this all of a sudden? Ac works fine in case you are wondering. Tried searching the forums but couldn’t really find an answer for my specific situation. Thanks for your help!

 

Did you thoroughly bleed all air from the cooling system? Is the new t’stat the correct, unique part for the LT1? When the low coolant light came on, was the system level actually low? When idling, any time the coolant temp exceeds 226°F both fans should be running - are they? The two fans should switch to high speed at 235°F, roughly (or slightly above) the temp shown on your dash gauge.

Did you check the fusible links that supply 12 volt power to the fans from the red “+” box near the battery?

Do you have a scan device that would allow you to read the coolant temp directly from the PCM? That would show whether the gauge (sensor in driver side head) and PCM (sensor in water pump housing) temperatures agree.

 

as far as I know the fans are working properly. I did not bleed out the system. I popped off the old sensor and plugged in the new one right away to keep the antifreeze from leaking out as much as I could, then topped off the fluid. Maybe air got in the system when I swapped the part out? The thermostat should be correct. I had the radiator flushed and a new thermostat put in a month ago and the car worked perfectly until the low coolant light came on, I added a little bit of coolant to the overflow, but it wasn’t really low, so my next step was to change the sensor. The light went away, but now it overheats.I didn’t touch anything else. Just pulled the battery out, changed the part and put the battery back in. I will see if I can figure out how to bleed the system and see if that helps.

 

If it's only going to 235 it is running hot, not overheating.

Did the coolant level sensor replacement occur around the time Seattle started experiencing record high temperatures?

But if I understand your answers, you didn't actually check the fan operation, you aren't absolutely sure you have the correct t'stat, and the system has not been checked for air. If the coolant isn't to the very top of the fill neck every time you check it, it's possible there is air in the system. The LT1's reverse flow cooling system cannot tolerate any air.

Is it possible the overflow hose to the reservoir is cracked or damaged? That will prevent the system from refilling itself as the radiator cools down, because it can't draw the vacuum required to pull replacement coolant from the reservoir.

 

I think I fixed it now. Just had an air bubble that needed to be bled out. Runs at a little under the halfway mark on the temp gauge and is holding stable for now. Thanks everyone!