So about a week ago I got the "service engine soon" light on my 01 GTP. When i plugged in my scanner is was something to do with the thermostat, coolant, or engine heat in general (sorry i forgot the exact code lol). Lately I've been noticing that my average economy in the city is between 12 and 13 mpg, nothing more than lukewarm air blows out of the vents (even after she has been running for 20 minutes or longer), and her engine temp is only a notch or 2 above 160 (again, I drove her to school today plus let her run 5 minutes before leaving so thats about 20-25 minutes.)

The first and only thing I have checked has been the coolant levels in the reservoire. The coolant was really low in the tank, but I saw 2 lines on the side of it that read "Cold" and just above that was "Hot". Is the coolant supposed to sit real low in the reservoire? Besides that I havent check the coolant in the radiator, thermostat to check if its stuck open, or the heater core.

How do I check to see if the t-stat is stuck open? Where is it even located?

Thanks

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I'd replace the thermostat. Sounds like it is partially open or something.

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One Big Ass Mistake America

Here's a write up for you: How To: Thermostat Swap

I bought a new tstat from O'Reilly for $10 and am going to give it a shot. The write-up looks nice, quick, and easy. Thanks for the help.

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Yeah...it is literally a ten minute job at the most.

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One Big Ass Mistake America

most def a bad t-stat. unlike older t-stats that stayed closed when they went bad causing the car to overheat...new ones stay open when they go bad.

if your radiator hasnt been flushed...might be a good time to do so also. and make sure to "burp" the system and get all the air out

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2000 Grand Prix GTX (32K) sold Oct 2009
1998 Grand Prix GT (102K) Totaled 1/7/2011
2006 Impala SS (48K)

My first attempt at switching out the t-stat was a complete failure. I spent about an hour trying to get at the lower left bolt. I don't have any tools that can get around or behind all the wires, hoses or clips that are in the way. Any suggestions?

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Do you have a friend with tools, it really shouldn't be difficult at all. If you have to, you might want to invest in a cheap socket set or something.

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05 GTP, TOG's , 3.5 pulley, ZZP 1.9 rockers, K&N CAI, OVERKILLED, poly mounts, GMPP suspension, F-body brakes

Mine has been that way for over a year. I've just been too lazy to change it. Besides, I like my car running cool down here. BTW, the coolant does sit very low in the resevoir. At least I know it does in an 04+.

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3.5" MPS, 1.84 Rockers, 3" DP, Frt PEM, 39lb Injs., PowrTuner, Wizair
14.07@ 98.85mph 2.180 60'

If replacing the T-Stat doesn't help, I would check out the Engine Coolant Temperature sensor. The easiest way is to check the scan tool to see what temperature it reads, then put some kind of thermometer on the coolant to see if it is close. If it is, and the coolant is disappearing with little to no heat, then take a look at my old post.

3800-engine-l36-l26-f17/stock-intake-problem-read-this-t10800.html

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2000 Pontiac Grand Prix GT