erratic temp gauge in my 95 chevy

SDE · Oct 8, 2014

The gauge has always run around 210, so I changed the thermostat. (195) The week before I put new intake manifold gaskets in it. Tonight I drove it and it got up to about 225. The upper hose was still cool. I backed it into the ditch and burped the engine by removing the radiator cap. The upper hose got warm immediately. Now the temp gauge will wander from 200 to 220 as I drive it. When I turn it off, the needle goes to the far right, instead of back to 100, like it should. Is this a ground wire problem and if it is, where is it?
Thank you
SDE

D beatty · Oct 8, 2014

My 97 GMC with 5.7 Vortec that wonders between 165 and 215 . I have changed thermostats ( now has a fail safe thermostat) cap and sending unit and still does it.I think mine is in the gauge it self and would mean dash take out and if it comes to that I will put in a gauge under dash.

rabbit-1 · Oct 8, 2014

Make sure all air has cleared the cooling system before doing any thing drastic.

Dalex · Oct 8, 2014

Google GM step motors , it's a defective dashboard circuit....

SDE · Oct 8, 2014

Would that have anything to do with the left side of the dash not being illuminated when the lights are on?

Dean · Oct 8, 2014

Bingo.

Most likely, you will soon have other dashboard symptoms, e.g., tachometer, fuel gage, etc.

Dean

SDE · Oct 8, 2014

Thank you. I checked out a video on the repair. Looks simple, if you have some skills with soldering.
SDE

ericy · Oct 8, 2014

My 92 chevy is doing That same thing 1 time the gage shows hot then after a short time it shows ok I too chaged the rad. new hoses new thermastat new sending unit its got to be a bad ground and yes my gas gage is way off and the other gages read slow or act goofie at times

Bob · Oct 8, 2014

Only one problem with that theory... the pickup gauge clusters using stepper motors didn't appear 'til '99!

Dave Salway · Oct 9, 2014

When my 97 acts up it is usualy a
ground problem.

MarkB_MI · Oct 9, 2014

You're putting one and one together and coming up with three. Just because the needle on your gauge goes to the right peg when you turn off the switch doesn't mean the gauge is bad. Those are "balanced" gauges as I recall; they don't necessarily return to zero because there's no spring on the needle.

You said you "burped" the engine. The fact that you (presumably) weren't seriously seriously scalded tells me the engine was WAY low on coolant. Are you sure it is FULL of coolant now? You need to get all the air out of the engine. This may take several iterations of topping off the radiator and driving it before all the air has been worked out.

It doesn't sound to me like there was a problem with the original thermostat. An engine with a 195 degree thermostat SHOULD run around 210. In fact, if it never gets any hotter than that it could indicate a coolant leak (because water boils at 212 at atmospheric pressure). Hmm, you say you replaced the intake manifold gaskets; was there a leak?

Dr. Walt · Oct 9, 2014

If you are refering to the Temp Gauge in the Instrument Cluster, it all Grounds through the Circuit Board and the screws that hold the Circuit Board into the dash. I had the same problem on my '88 GMC P/U, and finally had to put a separate Temp Gauge on the bottom of the dash.

:>)

souNdguy · Oct 9, 2014

Half the gauges in my 2000 Yukon quit before we replaced it a couple months ago.

Sprint 6 · Oct 9, 2014

95 is a simple setup for temp. The cluster is not your problem. In my experience, an erratic temp after a thermostat replacement is usually due to a low quality thermostats. I personally only use OE or Stant premium thermostats due to this very issue. Cheaper thermostats cannot maintain a consistant opening for some reason..

Hobo,NC · Oct 9, 2014

You have not proved the gauge right are wrong so lets say its right you have ran it till its up to operating temp you have a cool top hose... That's not good...

If it has a throttle body It may be possible you installed the Intake gasket on backerds... EZ check is to siffer the coolant out of the rad remove the top hose if coolant is still in the thermo neck the gasket is on backerds... If you are still unsure run a wire into the front coolant channel that goes to the head to check for blockage....

Its a beach to bleed all the air out of the system unless you have the tools to do it...

If all that checks out you may have to remove a heater hose to burp the air out...

The last chebby I ran into with the intake gaskets on backerds had been run a few years that way :shock: It was about this time last year and they were complaining of a no heat are poor heat issue (I Think)... I have ran across this were there were no complaints other than I saw issues with the temp gauge that were not normal while working on other issues not related to temp..

I had one you could drive it about 4/5 miles the temp would run up close to hot. Shut it off take a look see no issues (other than the top hose was cool to the touch) start it back up and it would run all day till it cooled down then it would repeat the issue...

littlered1 · Oct 9, 2014

I have a '94 Chevrolet pickup with the 5.7. The temperature gauge began acting up--jumping around and pegged on H. Popped the hood and the motor was as cool as it could be. Found out there were two sending units for temperature--one for the computer and one for the dash. The one for the computer is in the manifold near the thermostat and the one for the dash is in the drivers side head. Replaced both and I was good to go. I also replaced the thermostat and hoses as a matter of course. Now the temp needle sits rock steady.

luv2wrench · Oct 9, 2014

HOBO IS RIGHT.

make sure you didn't install intake manifold gaskets backwards. The restriction plate goes to the rear of the motor.

make sure your ground wire on top of the thermostat bolt is ok. that motor uses two temp sensors, one for ECM & one for the guage. The temp sender on the driver side bank is your guage sender.

SDE · Oct 9, 2014

I just changed the spark plugs. Maybe I bumped it. I know that the wire is a sloppy fit on the terminal.
Thank you
SDE

SDE · Oct 9, 2014

The temp got up to about 225. I stopped and checked the upper hose. It was cool. I backed the truck into the ditch, with the front tires on the shoulder of the road. I loosen the cap slowly, with the engine off. The coolant was very nosily making its way back into the reservoir. I started the truck and added a little coolant and checked the upper hose again. It was warm. I drove the truck another 10 miles and the heater as really throwing out the heat. After a couple of hours. I drove it back home and the gauge was going up and down about 20 degrees.
Thank you
SDE

Hobo,NC · Oct 9, 2014

If a bad connection at the sender seams to satisfy ya just disconnect it and record what the dash gauge reads... Post back with your results...

Bob · Oct 9, 2014

Just curious, do you understand how a "fail safe" thermostat works?

If the "fail safe" thermostat FAILS and never opens, it cannot enter the "locked open" "failsafe" mode. NOT so much failsafe in that situation!

On the other hand, if you break a fanbelt, or some similar catastrophe happens, and the engine gets hott'r than 'ell and the 'stat responds accordingly and opens more than normal a metal locking device keeps it from ever closing again, just before it craps it's guts out from the heat.

Hobo,NC · Oct 10, 2014

(quoted from post at 08:01:12 10/10/14) Just curious, do you understand how a "fail safe" thermostat works?

If the "fail safe" thermostat FAILS and never opens, it cannot enter the "locked open" "failsafe" mode. NOT so much failsafe in that situation!

On the other hand, if you break a fanbelt, or some similar catastrophe happens, and the engine gets hott'r than 'ell and the 'stat responds accordingly and opens more than normal a metal locking device keeps it from ever closing again, just before it craps it's guts out from the heat.

Nope never knew that I will look for it... I have seen a few stuck open and a few that came apart... As usual your knowledge is impressive 8)

erratic temp gauge in my 95 chevy

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