Problem with temperature gauge

[97silverdoe]

Hey everyone, this is my first post on here.

I purchased a 1997 Chevy Silverado K1500 with around 229,000 at the time. Over the past 6 months, I've put about 5,000 miles on it, and it's been a great truck!

However, I'm having a little issue with the temperature gauge. It keeps fluctuating all over the place. It will go from 130 degrees up to around 230 degrees Fahrenheit, back down repeatedly, and won't hold a stable temp.

I've flushed the radiator, changed the air core motor in the gauge cluster with a refurbished one, changed the two coolant temp sensors, and changed the thermostat. Nothing has solved the issue. It still does the same thing.

I'm wondering if anyone would advise me on what this issue could be and if the truck is still safe to drive like this. Thank you!

 

[RichLo]

Sounds like you've done everything right so far. I would try a cheap parts store aftermarket gauge kit before you change anything else.

Theres a few ways to flush the cooling system... poor, good, better, best. Lol.

Poor: drain the radiator and refill with 50/50 mix

Good: some combination of draining the radiator, flushing with water, running engine up to op temp and repeating until water looks good.

Better: Above but with radiator flush solution

Best: Drain radiator and block, refill with water/ cleaning solution, run for a half hour or more to let the cleaner eat, pull heater core hoses and flush/back-flush multiple times, same with radiator, drain the block, then refill. The garden hose flush/back flush knocks out more junk than any drain and fill can do.

If its really bad, you can do 'Best' a few times before the final refill.

Which one did you do? How did the flushed fluid look coming out?

 

[GrimsterGMC]

Does it work its way up and down slowly or does it change readings in an instant?

 

[97silverdoe]

Sounds like you've done everything right so far. I would try a cheap parts store aftermarket gauge kit before you change anything else.

Theres a few ways to flush the cooling system... poor, good, better, best. Lol.

Poor: drain the radiator and refill with 50/50 mix

Good: some combination of draining the radiator, flushing with water, running engine up to op temp and repeating until water looks good.

Better: Above but with radiator flush solution

Best: Drain radiator and block, refill with water/ cleaning solution, run for a half hour or more to let the cleaner eat, pull heater core hoses and flush/back-flush multiple times, same with radiator, drain the block, then refill. The garden hose flush/back flush knocks out more junk than any drain and fill can do.

If its really bad, you can do 'Best' a few times before the final refill.

Which one did you do? How did the flushed fluid look coming out?

Sounds like you've done everything right so far. I would try a cheap parts store aftermarket gauge kit before you change anything else.

Theres a few ways to flush the cooling system... poor, good, better, best. Lol.

Poor: drain the radiator and refill with 50/50 mix

Good: some combination of draining the radiator, flushing with water, running engine up to op temp and repeating until water looks good.

Better: Above but with radiator flush solution

Best: Drain radiator and block, refill with water/ cleaning solution, run for a half hour or more to let the cleaner eat, pull heater core hoses and flush/back-flush multiple times, same with radiator, drain the block, then refill. The garden hose flush/back flush knocks out more junk than any drain and fill can do.

If its really bad, you can do 'Best' a few times before the final refill.

Which one did you do? How did the flushed fluid look coming out?

Thanks for the reply and info! I went with the “better” option and used the Prestone cleaning solution, filled the radiator with water, and drove the truck for about an hour or so.

However, I didn't pull the radiator plug. I ran the engine for a second with the radiator hose off to get all the water out. (Maybe not the smartest thing on my end).

It looked like a lot of debris came out, though.

I then flushed the system with a garden hose till it was clean and refilled the system with coolant.

I might try an aftermarket gauge kit. That sounds like an excellent idea!

 

[97silverdoe]

Does it work its way up and down slowly or does it change readings in an instant?

Thanks for your response!

It works its way up slowly to about 230 degrees and then slowly back down to around 130-150.

 

[GrimsterGMC]

When flushing the block it is worth taking the knock sensor out of the passenger side and the plug on the drivers side. Then poke a screwdriver into each hole to break up the debris that settle and block the holes. Only then will you have drained the lower half of the block and that is where most of the debris sit between the cylinder walls. You will be surprised the amount of black flaky material that comes out the first time you do this.

 

[Schurkey]

WHAT ENGINE???

I didn't pull the radiator plug. I ran the engine for a second with the radiator hose off to get all the water out.

Dropping coolant via the lower rad hose doesn't even get close to draining "all the water out".

It will drain the radiator, and the block to the level of the water-pump openings in the block.

When flushing the block it is worth taking the knock sensor out of the passenger side and the plug on the drivers side. Then poke a screwdriver into each hole to break up the debris that settle and block the holes. Only then will you have drained the lower half of the block and that is where most of the debris sit between the cylinder walls. You will be surprised the amount of black flaky material that comes out the first time you do this.

^^^ Quoted for truth.

Big-blocks have drain plugs on both sides, the knock sensors are in blind holes.

Small-blocks have a drain plug on the left, and the knock sensor on the right.

I don't know for sure how the V6 is set up, but I bet it's like the small-block.

Once I get the original steel/iron plug(s) removed, I reinstall brass drain plug(s) or--on my own vehicles--brass draincock(s).

If you have to remove the knock sensor, remember that it needs to be installed with a torque wrench; the sensitivity of the knock sensor is affected by how tight it's screwed-in.

 

[GrimsterGMC]

WHAT ENGINE???


Dropping coolant via the lower rad hose doesn't even get close to draining "all the water out".

It will drain the radiator, and the block to the level of the water-pump openings in the block.


^^^ Quoted for truth.

Big-blocks have drain plugs on both sides, the knock sensors are in blind holes.

Small-blocks have a drain plug on the left, and the knock sensor on the right.

I don't know for sure how the V6 is set up, but I bet it's like the small-block.

Once I get the original steel/iron plug(s) removed, I reinstall brass drain plug(s) or--on my own vehicles--brass draincock(s).

If you have to remove the knock sensor, remember that it needs to be installed with a torque wrench; the sensitivity of the knock sensor is affected by how tight it's screwed-in.

I hadn't thought of a draincock but that is a really cool idea considering how hard it is to get a spanner in there.

 

[Orpedcrow]

It keeps fluctuating all over the place. It will go from 130 degrees up to around 230 degrees Fahrenheit, back down repeatedly, and won't hold a stable temp.

I know you said you changed the thermostat, but these symptoms sound like a lazy thermostat to me.

Could still be air in it too. A bubble around the temp sender will cause it to read real high.

 

[HawkDsl]

Check Grounds. A dirty rad or dirty water has little effect on temp gauge. It's measuring heat, not how dirty it is. Even coated with gunk, it'll read the temp, as the gunk will certainly conduct heat to the probe. I think you have an electrical issue, most likely grounds for the gauge cluster. your gonna have to get under there and check your wiring. Search for wiring diagrams in the form, there is a pinned post with all the factory manuals for certain years. Good Luck!