Temperature Gauge GMC fluctuations

[Redright9]

Hello,

My 2003 GMC Sierra 1500HD with the 6.0 has a fluctuating temperature gauge. It doesn't appear to overheat and the gauge doesn't read that it is getting too hot, but just seems to move more than it should. When at operating temperature it seems to move from 180-200. It will go back and forth from one to the other and sometimes stay cooler then hotter... The thermostat and water pump were replaced very recently along with the mechanical clutch on the fan. I am thinking this is the mechanical clutch coming on and off, but wanted to see if others have the same thing in their GMC's..

 

[clinebarger]

OE Thermostat?

 

[Big E]

Sounds normal to me. Coolant in the engine warms up, thermostat opens and lets cool coolant in from the radiator. Thermostat closes and the cycle begins again.

Both my '96 and '16 Cummins powered Rams do/did this.

 

[Redright9]

Yes, OE thermostat.. I figure its normal, but most other vehicles I have owned (even other GM trucks) the gauge would stay fairly steady.. Just looks weird seeing it move so much...

 

[billt460]

I wouldn't worry too much about it. My F-150 will rise to almost the middle of the gauge on a warm up from a dead cold start. (About to the "R" on the "NORMAL" lettering range on the gauge).

Then, once the thermostat opens it goes down to below the "N" on "NORMAL", and stays there, regardless if it's 40 F outside, or 115 F and I'm pulling a trailer. And it's on it's 3rd thermostat, (180 F), and has done the same thing on all 3 of them.

 

[Lubener]

Connect a scan tool and read the temperature data that the computer actually sees. I suspect a sending unit or gauge problem. Once open, themostats don't open and close back and forth randomly while you are driving.

 

[Jetronic]

yes they are constantly moving, as the heat production is constantly changing. If you look at obd temperatures you can see this.

Most cars have dummy gauges for that reason, people get nervous to see 20F fluctuations

 

[MParr]

Those wonderful gauges on GM products of that era, they are a sight to behold. However, it’s normal to see some fluctuations as the thermostat opens and closes or the cooling fan kicks on and off.

 

[390pcode]

I have a 2000 Suburban 2500 6.0. All OEM cooling parts with exception to the radiator which is an aftermarket Spectra Premium with extra fins/rows than OE. Now, if I'm going on a long downhill with ambient temps under 50* the temp will drop 20-30* Temps never move when pulling 11,000# uphill in 110* ambient, so that's good. Regular driving, no temp swing; stays a hair under 210*

 

[mrsilv04]

I have a 2000 GMC Sierra and 2004 Chevy Silverado. Your truck and these trucks are all from the same generation (GMT800).

I see no variation in the temp needle once it is up to operating temperature. Check and make sure that your radiator fins aren't clogged with dirt, dead bugs, cottonwood or cattail fluff, etc. Make sure it is good and clean. It's a cheap and easy thing to check. I had this problem with my 2000.

 

[D60]

Connect a scan tool and read the temperature data that the computer actually sees. I suspect a sending unit or gauge problem. Once open, themostats don't open and close back and forth randomly while you are driving.

My thoughts, too. A flakey stepper motor is always a possibility

 

[Tman220]

Yes, OE thermostat.. I figure its normal, but most other vehicles I have owned (even other GM trucks) the gauge would stay fairly steady.. Just looks weird seeing it move so much...

Is your heater core still hooked up
Do you have a coolant shutoff installed in the heater lines?

Worth the ask since I see you're from a warmer state. I have seen people try to re-engineer those things and create problems. The loop between the two nipples on the water pump for the heater core require constant flow.

 

[dishdude]

Those wonderful gauges on GM products of that era, they are a sight to behold. However, it’s normal to see some fluctuations as the thermostat opens and closes or the cooling fan kicks on and off.

Because they actually show an accurate reading! Oil pressure, coolant temperature and voltage should fluctuate.

 

[MParr]

Because they actually show an accurate reading! Oil pressure, coolant temperature and voltage should fluctuate.

If you ever owned or drive a GM product form that era, you would know those instrument panels were not worth a plug nickel.

 

[ls1mike]

If you ever owned or drive a GM product form that era, you would know those instrument panels were not worth a plug nickel.

Had an 02 2500HD and an 04 1500. While the stepper motors will go bad, they do provide a real reading.

OP both of mine were always rock solid. How many miles on the truck?

 

[Redright9]

My truck has 102k on it. Everything is hooked up and factory/OE parts. I know it is not much of a temperature swing, but it the way the gauge is, it makes it look like a lot (since that 20ish degrees is about a quarter of the gauge). I am thinking its the clutch fan engaging and disengaging....

 

[ls1mike]

My truck has 102k on it. Everything is hooked up and factory/OE parts. I know it is not much of a temperature swing, but it the way the gauge is, it makes it look like a lot (since that 20ish degrees is about a quarter of the gauge). I am thinking its the clutch fan engaging and disengaging....

Yeah I wouldn't worry about it. My 02 was pretty solid, but it would move from time to time.

 

[Tman220]

My truck has 102k on it. Everything is hooked up and factory/OE parts. I know it is not much of a temperature swing, but it the way the gauge is, it makes it look like a lot (since that 20ish degrees is about a quarter of the gauge). I am thinking its the clutch fan engaging and disengaging....

When the clutch fan locks up it is absolutely unmistakable. They make an incredible racket and probably require 10 hp at 2000 engine RPM, they are that loud. You would know without a doubt if/when it locks up.

On cool mornings you probably hear the fan make more noise compared to when it's warmed up. Multiply that noise by several factors for lock up while driving.

 

[xmanjeff]

i have an 2003 silverado that had thefuel gauge acting wonky and apparently the gauge cluster has been a known problem , do a google search and you will come up with some info , i sent mine out to get redone , all good for the last few years