Thread: 97 Grand Prix Running at High Temp

I have a 97 Pontiac Grand Prix GTP, 3.8L supercharged engine. Last week I received an SES code indicating low voltage input from the engine coolant temperature sensor. I replaced this sensor. Ever since, the car has been running much hotter than it has always run. The car previously always ran around 170, always. Now it runs 210 to 215. Also today I noticed that at highway speed (65 mph), the temp would climb to like 235 or so, the fans would kick on and the temp would come back down to like 215. It would continually go up and down like this rather quickly while at highway speed, but at a stop, the temp would stay just above 210. This seems opposite of what should happen. The radiator is less than a year old. I pulled the cooling system apart the other day, and the water pump seems to be ok. I flushed through the block and the radiator and they seemed to flush through ok. I have replaced the t-stat, radiator cap. The hoses do not appear to be collapsing, at least at idle. Could they be collapsing at speed? I am at a loss here as all that I did was replace the temp sensor.

Sorry about the two threads. Won't happen again.

I am concerned about a possible gauge problem as, according to the gauge, the thermostat doesn't open until a temperature much higher than the 195 degrees the thermostat is rated at. How does the gauge get its input? Is it from the computer module, or is there a direct line from the coolant sensor itself? The thermostat is new, and the coolant was changed over the green type coolant quite some time ago. Thanks for everyone's help so far. It is greatly appreciated.

I am going to measure the resistance across the temp sensor. I would use the green and black wire pins right? (as there is also a yellow wire and associated pin). Also if I measure the voltage across the green and black wires coming from the PCM with the engine on, I should get 5 volts right?