1996 Sierra Thermostat Gauge going BONKERS!

[tjkmoney]

Thank you for this Forum!!

I have recently bought some M/T's and played in the mud last night.

I noticed the temp was on FULL, but when I would hit brakes, or hit a bump it would bounce from the normal operating temperature to 260.

Also when I shut the truck off, and turned the ignition forward the temp read in a normal zone.

I'm hoping it is a loose connection, or a thermostat?

No white smoke, antifreeze is full, I have had to replace water pump.

What gives? Thanks in advance!!!

Trevor

 

[GMCSierra3500]

Did you bleed the system well when you replaced the pump? Has it only done this on this day, or does it fluctuate randomly? Maybe it's a bad ground. Temp gauges are pretty simple. Maybe your thermostat does need replacing, how many miles on the truck, and was it ever replaced? I'm guessing like most GM vehicles, it has a 195* thermostat in it.

 

[tjkmoney]

Hey GMCSIERRA3500,

Thanks for responding!

Sorry I didn't explain the water pump. I changed that out last year, and I haven't had any problems... The incident last night was from mudding, it never has happen before this. Truck just hit 170k. Never had any major mechanical problems. Doesn't burn oil. Etc.

It has to be a ground IMO. Every bump I hit the gauge goes haywire and bounces all around.... When I am driving on flat ground it goes back to regular operating temp range between 180-200 I think. But it is sticking at 260* the most frequently.

I am going to change the thermostat either way. I am just trying to find out where the ground is for the thermostat mainly.

Where is the thermostat ground?

 

[GMCSierra3500]

Do you have a multi meter? You could check for resistance in the temp sensor harness to see if there is a break in the wire, maybe making the connection intermittent. Or get the truck up to temp (like you said, around 200*f), and jumble around the harness. I just had to do the same on my Grand AM's wheel speed sensor harness. The harness' get breaks in them from stretching over the years (GM made the harness' a hair too short), so i probed with a multi meter, found the section that broke, cut it out and soldered in a new piece. Come to find out, it broke internally, corroded and caused an intermittent connection. You could also test the sensor to see if the sensor is bad, with the DMM. Do some searching online for these procedures. Do you have access to a code scanner with live data? Maybe plug in, and reference the gauge to the numbers in the scanner. The temp sensor will look like a brass bolt maybe 15mm? with a black oval plug ontop of it. My guess is in the side of the engine, passenger side. I could be wrong on location (i'm not famaliar with these trucks just yet, my buddy just got his).

 

[GMCSierra3500]

Actually, my buddy had a k2500 before this (a 1998), i don't know if the 96 and 98 are the same, but if so, and if you can't figure it out, i could take a peak in the book and scan some pages in if you wish.