After getting my car back from the shop, the techs there noted that the car is running cool, and asked if I had a 160* thermo in it. No, but I did swap the 195* out when I got the car because of a SES error and dropped in a 180*. However, I thought that unless the PCM is reprogrammed to recognize the 180*, it doesn't matter. So I guess two questions here.

1. Does simply putting a 180* thermo in without changing the PCM make a difference?
2. Can an engine run too cold? I never saw the temperature guage go over 195 today after some 1-2 hours worth of highway driving today, mixed with a little city driving.

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2004 Impala SS - ZZP PCM, 3.4" Pulley, K&N CAI, TOG Headers, SLP Cat-Back, 180* thermo, Autolite 605s, PRJ Performance wires, Alternator rewire, GMPP Handling kit
2000 Grand Prix GT, Commuter Car - K&N CAI, GMPP Handling kit, ZZP downpipe w/U-bend delete, ZZP Plog, Alternator rewire

The 180* T-Stat will allow it to run cooler obviously and you dont need to change or program the PCM to do so as far as I know. If you look at the temp gauge, there are four major marks on it and two smaller marks between each of those. GM and their techs would have you run an engine temp that puts the needle at the middle of the gauge. Ive asked GM mechanics before and was told they like to see about 200 - 210 which to me is a bit too hot.

The 180* T-Stat I run (its drilled also) puts my cruising temp just above the first major mark, usually about the first minor mark after that and it will go up and down around there. In town it will go up some but I have my PCM programmed to kick on the fans around 185 I believe.

You can indeed run an engine too cold. If your thermostat were ever to stick open you will find that it will run cool enough to cause some stumbling at idle and you will most certainly use a bit more fuel. 180* is about the coolest thermostat I would ever use in a passenger vehicle.

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Scotty Hall
Bartlesville, OK
2001 Pontiac Grand Prix GTP
It whines a lot, but I like it.

The only limitation you will ever face in life is yourself!

I'll keep an eye on it then over the next few weeks. From the code I was given, I also read that it could be a bad temperature sensor. I don't think the new thermo is stuck open, and there's been no code thrown since I put the new one in and cleared the error. But could the bad temp sensor keep the coolant flowing? There's been no stumbling at idle, and a quick computation of the MPG average was 24, a mix of highway and city. About right. Then again, maybe the gauge is just wrong. I believe my ODBC2 code reader might also monitor temperature. Worst case, I get the Aeroforce gauges to go in the Impala pillar gauge holder and check it out in the GP for a while.

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2004 Impala SS - ZZP PCM, 3.4" Pulley, K&N CAI, TOG Headers, SLP Cat-Back, 180* thermo, Autolite 605s, PRJ Performance wires, Alternator rewire, GMPP Handling kit
2000 Grand Prix GT, Commuter Car - K&N CAI, GMPP Handling kit, ZZP downpipe w/U-bend delete, ZZP Plog, Alternator rewire