Heat Guage Goes Up when idling for awhile

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.

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

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.

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.

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.

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.

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?

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.

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 :lol2:).

I will let you know if they have any input.

Take care,

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

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.

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?

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.

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.

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.

I know you installed a new thermostat - but - perhaps its faulty?

I think your real concern is the FANS not kicking in when you think they should, right?

You may have a trapped air bubble.

Would trapped air make the guage go up only when idling? And if so how do you bleed the cooling lines?

Would trapped air make the guage go up only when idling? And if so how do you bleed the cooling lines?It did at the begining stages of my head gasket. Idling would slow the water flow, so air would be trapped around the top of the tstat housing. Once I started going, water flow increased, pushing the bubble out of the way. Or at least that was my theory on the situation.

There are two bleeder screws, one on the top of bypass pipe on top of the water pump and one on the tstat housing where the upper radiator hose attaches. When I bleed my system of as much air as possible, I fill it, let the engine reach operating tempature with both heaters set to high with the blowers running, then open the bleeder screw just slightly to allow any air to escape, then tighten when a little coolant starts to appear. Slowly start to open the radiator to the vent position. This will allow air pressure to escape to the resevoir tank. After you stop hearing the pressure being released, tighten everything back up. Allow to cool. Repeate several times. Each time you equalize the pressure in the system to the same as the atmosphere. Then as air left in the system cools, it will create a vacuum sucking in coolant from the resevoir tank. Every time this happens, a little more air is worked out of the system. The same thing will happen during the normal operating of the vehicle, just my way speeds it up a little quicker.

In my case, I quickly figured out that air was working it's way back into the system by way of the head gasket though.

Just to let you folks know, I talked to the service tech at the dealership today on the phone. The said "Its supposed to work that way." He couldn't (or wouldn't) give me ANY more information without coming in and having some service done.

Not much help there. Maybe I will try another GM dealer.

I have read somewhere in this forum that venture temp guage works that way, hopefully it does.
Any code scanner can monitor the temp on th engine? there is an actron scanner here for a loaner, i might try it tommorow, hope it works.

Any code scanner can monitor the temp on th engine? there is an actron scanner here for a loaner, i might try it tommorow, hope it works.My Actron CP9145 will read sensor data real time. I think all of the lesser models, typically found at part stores for reading DTC will not read actual sensor data. Only report the DTC numbers (and description depending on model).

Just thought I would let you folks know that I have upload some information about how and when the engine cooling fans are SUPPOSED to operate. See link below.

http://www.my-chevy-venture.com/engine-cooling-system.html

One other note: My A/C didn't want to operate today (no cold air and no "click" when I pushed the button).

When I got home, I opened up the under-hood fuse box and "tapped" on the relays with my fingers. Guess what - Heard a "click" and the A/C is working again. I guess I gotta get in there and see if a relay is going bad, or perhaps a bad/loose connection.

Take care,

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.

Those of us who have gone through the intake manifold gasket leak thing may well be a little parinoid. Obviously, you have not. It is expensive, many of us have been missled and spent a great deal of money trying to solve a overheating problem. It's not a minor issue!

Deny

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.

Did you ever solve this problem I am having the same thing and I am told there is a good chance it's the PCM

Has anyone found a solution to the this "no fan on unless you turn on the AC" Anyone

Has anyone found a solution to the this "no fan on unless you turn on the AC" Anyone

Try unplugging the Engine Temperature Coolant Sensor, and the fans should come on full. That should direct you somewhere.

http://i195.photobucket.com/albums/z130/jorgvankleef/Chevrolet%20headgasket%20job/IMG_0250.jpg

Its the wire with the purple top, near the thermostat housing.

http://i195.photobucket.com/albums/z130/jorgvankleef/Chevrolet%20headgasket%20job/IMG_0240.jpg

Right under throttle body and behind engine mount.

This might tell you if PCM is bad, or your fans come on late (which is how its supposed to be)

Yes I did unplug at the coolant temperature sensor and yes the fans did come on at hi speed. All this says to me is that the fans are running ok I knew that by simply turning on the AC the fans came on.

My guess is the ECU is not sending the ground signal to the fan relay. How do I test this????