'98 Temp Gauge Mystery

[ACMercker]

During a normal warm-up, my Temp Gauge jumps right up to pegged when it passes an indicated 168 degrees. She just shoots off the chart way above 260 and stays there. Funny thing is... it doesn't seem hot. Seen it hot before too... my wife drives this one.

This is a '98 LS (192,000+ miles) with a Vortec 5.7, Auto w/OD, AC, 4WD... blue... for what that's worth.

Am I looking at a sensor gone bad, maybe? sending unit?

Need help on this one... All help much appreciated in advance. Thanks

ACMercker

 

[ACMercker]

Cycled the motor again... same thing... warms up to 170 degrees or so and then pegs the needle. -ACM

 

[1999HOE]

Tahoeyukonforums

 

[ACMercker]

Morning Update

Drove the lil' Tahito a mile or so this morning to drop our crum-cruncher off at school.

Here's what happened... the temp gauge read about 120 degrees when I got to the school where I cut it off for 5 min. or so for the delivery.

On restart, the temp gauge pegged above 260 degrees again. So I headed home. about 300 yards from the school, the gauge dropped back, kind of slowly to maybe 140 degrees and started to climb slowly, like normal. By the time I got back to the house it was up to around 160 degrees. I stopped in the driveway to watch what would happen next.

The temp kept rising like normal to about 170 and then it spiked to 210 but dropped back. It did this 2 more times but the rise was slower those times. It settled back at about 170 and then jumped to the peg above 260. I parked it.

What do you folks think?

I thought it might be the sensor but I'm not sure now...

Thanks again for any help coming this way.

ACMercker

 

[the 18th letter]

If you have no leaks I would check the thermostat. I tend to start cheap and work my way up the price ladder in terms of possible fixes. My .02

 

[ACMercker]

This is what I'm thinking too. Bought a thermostat and haven't put it in yet... we're snowed in. I'm glad to be on the same page with other folks on the forum. Thanks for the post "R" -ACM

 

[the 18th letter]

This is what I'm thinking too. Bought a thermostat and haven't put it in yet... we're snowed in. I'm glad to be on the same page with other folks on the forum. Thanks for the post "R" -ACM

I learned from exp that if you start having temp issues check that heater hose connect in the manifold also. Apparently GM has a problem with them breaking off in the manifold (since they sell a GM heater hose connect remover in the auto store). Mine broke off and luckily my mechanic was able to get it out and only charged me a 100 bux. Replacing that manifold is COSTLY.