Thread: Replaced temp sensor, now temp gauge stays pegged high...

Hi. Working on my 22 yr old son's 2001 Grand Prix GT (3.8l motor) again.

Started stalling when it gets to normal operating temperature, loss of power.

He works at Advance Auto so they threw it on the comp which told them
that the temp sensor was bad.

So we replaced the sensor, thermostat and top radiator hose. (gonna
replace the bottom one this week, looks like its trying to collapse a
little bit when you rev the motor up).

So we get it all back together and he starts it up. Takes off, no problem
there. However, both fans are turning all the time and the temp gauge
shows max high temp.

Since then, one of his friends told him that he needed to "bleed" the system
using the little screw on top of the thermostat housing, that a bubble of
air there was causing the problem.

Not had a chance to try it yet, is it as simple as that? Sounds too easy.

Thanks everyone.

Yep. Since you replaced the thermostat and top hose you introduced a bunch of air into the system. Get it up to temp and crack that bleeder screw open until you get a STEADY stream of coolant from it. Yes, it will leak all over the intake. That's fine. You will notice that it will spit air/coolant for a while. I usually crack it and let it bleed a bit, then shut it and repeat this several times so I don't flood the LIM with coolant.

Search for "cooalnt bleeding procedure" on here as this is a common issue with these motors.

Okay, we bled the system, replaced the bottom radiator hose, and replaced the
temp sensor with a new one (Advance claimed the first new one was defective).

So we did all that, and it's still doing the same thing.

The computer at Advance is still throwing a bad temp sensor code. The people
at Advance are claiming its the --> 2nd <-- temp sensor that's bad, not the
first one under the thermostat?

Is there a second one somewhere on these cars?

Thanks!

Umm, no. Not that I'm aware of. There is an intake air temp sensor and a coolant temp sensor. That's all I'm aware of. Did you replace the lower hose and temp sensor and THEN bleed the system, or did you do it in the order you listed?

I'd start checking the wiring to the temp sensor at this point. Might be bad somewhere in the harness or at the clip. Might be time to scan it and see what the temp sensor is actually telling the PCM.

Yeah, we're going to - right now, with the 2nd sensor from Advance, the fans have stopped
running all the time, but the temp gauge still stays maxed out when you turn the key on.

Local GM dealer didn't have one in stock, so we had to order it - should be here Monday.

I'll post the results once we get it in.

Thanks everyone.

Good news. We got the GM OEM temp sensor in yesterday and put it in. Fixed everything.
So the Advance model, whatever it was, was the problem after all.

Everything is working fine now, fans are coming on/off, temp gauge is reading correctly,
and all that.

The GM model was $30 vs $20 for the Advance, but heck, it works.

Thanks everyone for all the usual sage advice and help!