Heat Guage Goes Up when idling for awhile

[authenticy]

I have a 2000 chevy venture with 100,000 miles on it and I just had the thermostat replaced a month ago. Now that the weather is getting warmer I have noticed the guage going up when idling for a few minutes, drive through, etc. Is there a sensor that could have went bad when the thermostat went out that should be replaced? When I start driving again the guage comes back down. I have noticed that the fans arent kicking on, but when I turn the a/c or heat on then they do? Any thoughts would be appreciated.

[ChoochCharlie]

Sounds just like when I needed to change my sensor. It's a $20 part and can be changed in 15 minutes or so. At 100K miles your van is due for one. Mine went at 118K.
Could be a bit of air in the system too. Follow the directions in Haynes for bleeding the cooling system. There are two bleed valves.

Charlie

[jhong1226]

i have the same problem with my 2000, i have already changed the temp sensor but the problem still persist. i havent change my thermostat though but i think its not the thermostat since it cools down when fans are on or when running, means the coolant still is circulating.
i might try bleeding the cooling system for trapped air.
the only thing bothering me is that the fans dont kick in till the temp guage goes past half. it might be normal or its a problem.
if i could get an info on where the 220'f mark on the guage on these vans are, it would really be helpfull.
also if anyone has the steps in bleeding the cooling system,id really appreciate it.
keep us posted though for any progress on your problem.

[authenticy]

Had the sensor check by blowing heat on it and it made the guage go all the way to hot so sensor is working. Had the thermostat replaced already. Looks like the fans aren't kicking on when it gets hot. When I turn the AC on the fans come on and it starts to cool the car. It doesn't get hot right away unless I sit in traffic or in the drive through. Is there another sensor that makes the fans kick on? Or something that triggers the fans. I know the fans are working because they come on when AC is on.

[GregA]

Originally Posted by authenticy

Had the sensor check by blowing heat on it and it made the guage go all the way to hot so sensor is working. Had the thermostat replaced already. Looks like the fans aren't kicking on when it gets hot. When I turn the AC on the fans come on and it starts to cool the car. It doesn't get hot right away unless I sit in traffic or in the drive through. Is there another sensor that makes the fans kick on? Or something that triggers the fans. I know the fans are working because they come on when AC is on.

Just to let you know, my 2001 does the same thing (goes just above the middle mark on the gauge when in traffic before the fans turn on).

According to my manual, there is only one sensor for the coolant temperature. It is the PCM (Powertrain Control Module) that then turns on the fans.

My theory is that the system is programmed to run the engine hotter when idling for a long time to reduce emissions - but its just a theory.

[jhong1226]

Would GM tell you if these high temp we're having are normal? all of the vehicles that i had have theyre normal opertaing temp at the middle of the guage, this is the first tim ive had a vehicle that goes past half if iddling.

[cdru]

The thermostat opens at 195 degrees. Before that point, it's closed and the water just gets circulated around the engine. The guage is not linear. The bottom says 100, but in reality its more like 175 or so. Their are 4 smaller marks, then a large one IIRC. This larger one is just below 195. So the "normal" operating tempature is right there. The fans will not kick on until 235 and then kick of when it gets back to 215 IIRC. I may be slightly off on my exact tempatures as it was a week ago when I sat there and watched at exactly what tempatures things happened at with a scan tool.

In other words, it's normal operation for the tempature to fluctuate a little while idling. The engine just isn't circulating as much water. If it goes up more then a few ticks at a stoplight, I would check to make sure your coolant is at the correct concentration and level, your radiator isn't plugged, and you don't have air in your system.

My van had a head gasket leak that was pushing air into the system. My symptoms where similar, but very more pronounced as the problem progressed. Idling would have a slow rise then quickly jump to red. Just something to keep your eye on. Is your coolant level consistant, no drips on the driveway?

[jhong1226]

no leaks, coolant is still at max line in reservoir and radaitor is full at the cap.already bled the system, it wont overheat though just goes bout 2 lines pass half then the fan kicks on,goes back 1 or 2 lines below half. when driving at highway ,temp goes bout 1 line past 1/4.

[GregA]

Mine is almost EXACTLY the same behavior.

I think I'm gonna see if I can talk to the service guys at the local dealer and see if they have more info (to support my theory ).

I will let you know if they have any input.

Take care,

[jhong1226]

hope you find some answers though coz theres a lot of people with the same problem( or it may be normal).
keep us posted!

[cdru]

I hooked up my Actron scan tool up on my lunch break to observe where the tempatures are at. The first major mark is right at 195, the tempature of the thermostat. From there to 210 is a fairly linear scale. So if it's going two ticks past the 210 mark, you are probably still less then 215. It's 20 degrees past the thermostat, but still not overly harmful. It's possible that you have corrosion or other gunk acting as an insulator in the system, allowing it to run hotter as it's not as efficient at cooling. It could also be that your temp sensor is failing or your thermostat is sticking.

I wouldn't be overly concerned, but something to keep your eye on. What does your coolant look like? Has it turned brown or can you see things floating it it? Your overflow tank would also be gunked up. It may also be due for a coolant system flush.

[authenticy]

Just a curiousity question. I have just replaced the sensor to eliminate that possibility and of course it didn't work. Then next suggestion they are saying is reflashing the PCM, because this is what tells the fans to kick on. They have also noticed my van is idling low which will cause it to roll back on small hills and of course this is also regulated by the PCM so I figure for $80.00 it can't hurt. Any thoughts?

[bleepster]

people - i am not being calous to the situation, but if you are not overheating, and there are no "problems" - then whats the point???

a car sitting at idle is going to run hotter than one on the move. it seems you are insisting that there IS a problem.

[authenticy]

Originally Posted by authenticy

Just a curiousity question. I have just replaced the sensor to eliminate that possibility and of course it didn't work. Then next suggestion they are saying is reflashing the PCM, because this is what tells the fans to kick on. They have also noticed my van is idling low which will cause it to roll back on small hills and of course this is also regulated by the PCM so I figure for $80.00 it can't hurt. Any thoughts?

In my case there is a problem because I don't think having your guage go past 3/4, almost to RED IS NORMAL! The only way I get my fans to kick on is by running the A/C, and then the guage will return to just under half. It has always ran at about the 1/4 mark until I relplace the thermostat.

[cdru]

Originally Posted by authenticy

In my case there is a problem because I don't think having your guage go past 3/4, almost to RED IS NORMAL! The only way I get my fans to kick on is by running the A/C, and then the guage will return to just under half. It has always ran at about the 1/4 mark until I relplace the thermostat.

You may have a trapped air bubble.