So I keep getting P0128 codes once in a while so I decided to look into it and see what the problem is. Apprently the temperature is low and it doesnt warm up quite well... I had the car in park running for 3-5 minutes and the temp was at 110.

I decided to check up the thermostat first before going for the sensors and everything.

At first I thought there might be no thermostat in it afterall since the previous owner lived in Arizona..
I opened it and indeed I found a thermostat with the brand "WAXSTAT" and tested it in hot and cold water and it seemed to work fine. When its cold however the top part isn't sealed but I'm not sure if it should be or it shouldn't

Here are some pictures
http://i58.tinypic.com/s5ux6e.jpg
http://i61.tinypic.com/w6ql4l.jpg
http://i59.tinypic.com/2co67aq.jpg
http://i62.tinypic.com/2jb9ke9.jpg

So does this look okay?

 

I am thinking it should be closed all the way. Thermostats are inexpensive. I'd gamble the few dollars and change it.

 

P0128: Coolant temperature below thermostat regulating temperature. The PCM makes that determination if coolant temperature does not achieve operating temperature within a certain amount of time.

The thermostat should begin to open at 195F, and regulate ~ 198F to 200F.
Replace the thermostat and burp the air out.

 

Well yeah it turned out that it was supposed to seal all the way. I placed an order for the OEM delco from rock auto. And how does one "burp the air out"?
Thanks

 

BURP! Raise the right front corner of the vehicle so the radiator cap is the highest point. Remove the radiator cap. Bring engine to normal operating temperature. Raise idle to ~2Krpm. Keep the radiator full. Briefly rev the engine a few times to move any trapped air pockets to the cap, and out, (burp). When the coolant level stabilizes, increase and hold at ~3Krpm, fill the radiator to the top, install the cap, and then let the engine idle. Fill the reservoir to the "MAX" line.