97 Grand Prix Running at High Temp

[jpearsall187]

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.

 

[BillBoost37]

170 is cold for these cars. Stock thermostat is a 195F, many people swap that to a 180F. Even then, unless you get a pcm or program the fans down, they don't come on until 216F (low speed) and 228F (high speed).

Kinda sounds like that fluctuation you see is air in the system. Try and see if you can bleed any more air out.

 

[jpearsall187]

I can try bleeding out more air. How obvious is a collapsed hose? The upper one is new but the lower is probably original. A collapsed hose would be obvious wouldn't it? What temp are the cooling fans supposed to come on at?

 

[Bio248]

deleted your other thread. you only get one.

 

[jpearsall187]

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

 

[vincegpking]

I can try bleeding out more air. How obvious is a collapsed hose? The upper one is new but the lower is probably original. A collapsed hose would be obvious wouldn't it? What temp are the cooling fans supposed to come on at?[/QUOTE

Fan temps are stated in the post above. If your kicking on high speed st 228 you better start looking at some things

Are you actually running hot or just judging by your gauge? We get faulty parts at work more often than people think. Id say when your running hot swing by a shop and have them look at the scan data pod for ect. Make sure the gauge reads the same. If not get a new sensor.

If they match get a tstat cap and if you have orange coolant get that crap out of there because you may have coolant ports blocked as well

 

[jpearsall187]

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.

 

[jpearsall187]

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?