Cooling Issues

[mrobertson]

Truck is a 97 Tahoe LS w/ 5.7 V8 4x4.

I am trying to track down an overheating problem, or a problem with the gauge. Basically, truck warms up and the gauge will slowly climb to between 210 and 260. Then it will settle back down to about 210. Then creep back up, settle back down, creep back up, etc.

Truck has new head gaskets, new intake gaskets, new radiator, new 195 thermostat, and fresh dex-cool coolant.

Now - i have replaced the sensor on the block, drivers side middle.

My biggest question is - there is a sensor just slightly below the thermostat housing. Can anyone tell me what that sensor is?

Only thing that hasn't been replaced is the water pump and that sensor if it is relative. I bought an IR thermometer and shot it on the block where the sensor is on the block, reads anywhere from 170 - 195 when the truck is warmed up, gauge dash still reads 210 or higher.

So - what is that sensor just below the thermostat housing?????

 

[Diller]

That is the coolant temperature sensor. Your truck has 2. The one by the t-stat housing reads back to the ECM. The other one you have reads back to the gauge on the dash.


Diller
'99 Yukon SLT
'08 Hummer H3

 

[mrobertson]

Hmm - so the coolant temperature sensor would have nothing to do with what the gauge reads on the dash, correct?

 

[oldsalt]

Try putting the old block sensor back in and see if you still get the high reading.

Also, if you can, while the engine is hot plug in a scanner and see what it says for the temp.

Some of the people here have said that Autozone will hook up a scanner/code reader for diagnosis however I have never used them. I have a Scan Guage.

 

[SunlitComet]

the one on the left cylinder head reads on the dash. the one below housing is for the computer. You might have a damaged wire lead for that sensor that is shorting.

 

[noJeepshere]

the one on the left cylinder head reads on the dash. the one below housing is for the computer. You might have a damaged wire lead for that sensor that is shorting.

That's what it sounds like to me, there is too much resistance in the wire somewhere messing with the reading. I worry about the sensor in the cylinder head because of it's proximity to the exhaust manifold.

 

[mrobertson]

I'm bumping this up hoping for some love. I've added some new information

I replaced the water pump with a high performance one from Summit. Flushed the coolant again when i did it. So - new head gaskets, new intake gasket, new water pump, new radiator, new 195 thermostat, and fresh dexcool coolant.

Changing the water pump didn't make any change.

BUT - 1 think i've noticed. If i leave it sit for 2-3 days, and its less than 30 degrees here.........i go to start the truck. As soon as i start it, the temp gauge is already on 130 - 140 degrees......it literally NEVER goes down all the way.

I also have an S-10 and when i start it on a cold morning, the temp guage is all the way down at 100 degrees.

So - it's like something is stopping the gauge from going all the way down.

Any ideas?

 

[bridgeman]

The owners manual states 210 deg is norm range for temp. so warming up it would not be unreasonable for the temp gauge to go to 230 deg or so. Maybe the gauge is slow to react? If you want to know if the gauge is bad go get an after market gauge and hook it up to the sensor that should tell you if the gauge is working or not.

Bridgeman
99 tahoe 4x4

 

[SunlitComet]

that sensor creates resistance when cold. Hotter less resistance. Since you have replaced that sensor the wire has a small sort somewhere or the gauge is malfunctioning.

 

[99Yuk]

IDK about you guys, but my mechanical temp gauge drops to nothing when it's cold, and then moves up as it gets warm.
If this guy has replaced all the parts that would affect temps and his gauge doesn't move even when cold, maybe he has a gauge problem. A good way to confirm this would be to use a scan gauge tool like THIS. It's what I have to read real-time values from the computer while the truck is running. I've confirmed that my temp gauge is off a bit. (As is most of my mechanical gauges vs what the computer says the value is.)

Anyway you can read the real-time temps off of your trucks computer and not rely on the gauge?