Pontiac Repair: 1999 Pontiac Montana-Heads/Water Pump, water boiling point, pontiac montana

Question
I have a 1999 Pontiac Montana. I just got the heads and water pump fixed on the van because it was running hot. After the van has been fixed the thermostat gauge has been working its way back up to 210 which is past half way. They told me that I have to turn my air on to keep the thermostat gauge at half way, which I have been doing and it works. But why should I have to turn my air on to keep the gauge down? They stated that the thermostat was not replaced when the van was fixed. Can you give some advice on the thermostat gauge?

Answer
Hi
I will answer this from the info you gave, not knowing some specifics.
first off, YOU SHOULD not have to do ANYTHING. Whats gonna happen this winter?? Supposed to use your air? FYI< turning on the A/C your turning on the radiator fans. This is blowing air through keeping it cool. PLUS it is good to keep fans on at all times.
Let it run and see how high the gage gets....If it starts to get in red, turn on the air, to "cool" it down.
It MAY have an air pocket. They ARE responsible for getting the air pocket out, shoulda never left shop until it was out.
That being said, 210 is not hot for a GM.
The gage is relative. they are fairly accurate but not always. BEST advice.... take it back. Have them hook a scantool to the vehicle and observe the  Coolant temp sensor AND the Fan status. See if the fans turn on and at what temp. A GM turning on fans at 223-229 is NOT uncommon.
You must remeber thats only (about) 10* above water boiling point.
If the fans turn on ANYWHERE up to say 226 and they'll turn of USUALLY 15-20* below the turn on temp, thats operating normally.
Doing a major engine job does for some reason I am not totally sure of, but I have had it happen to me, seem to make these engines run just a bit warmer.
Also, make you more aware of things you MAY not have really noticed before or been so conscience of before.(not saying thats bad, I do it to.)
So take it back, in a good attitude, BUT also with the attitude that YOU just spent $2k or so on this job. Just want peace of mind, thats all.
I really hope this helps.
Good Luck
Follow post back, if needed.
Pawl