Screwy Water temp gauge?

#1

At the track today, while testing the new car, I noticed the water temp gauge was a little “jumpy.” Also, the fuel gauge read 1/2 when the tank was full, but read full during the next session.

Also, the temp gauge would creep up toward the red zone after idling for a while. I never let it get too hot, and turning on the aftermarket fan helped some but this engine always ran with the gauge needle just below the middle, in the old car. Ambient temp was about 40 degrees today.

Plus, if the temp gauge was creeping up to the 3/4 mark and I turned off the engine and then instantly turned the ignition on - no engine - the gauge would immediately read just below the middle. Then, I would start the engine and the gauge would immediately go to the 3/4 mark.

The top coolant hoses felt very warm but not so hot that I couldn’t hold them.

Has anyone seen this kind of behavior with a temp gauge?

Thanks,

Carter

#2

Carter,

Lots of times erratic gauges are a sign of a bad ground. Somewhere on here I was able to find what was thought to be the temp at the different readings on the stock gauge but don’t remember them exactly. An Lazer Pyromoter aimed at the T-Stat housing should be able to give you a very good idea of the water temp. They are around $40 now from Harbor Freight.

You could also check for a sticking T-stat.

Start with the gounds, Engine and batt.

Good Luck and keep us posted.

Michael
#36
Great Lakes Region

#3

With both gauges reading odd, it’s likely a bad ground as noted or even a bad cluster.

If you have another cluster (or can borrow one to test) you might give that a go.

On my previous car and some of Patton’s fleet, a smart whack on the top of the dash with palm of hand would give temp gauge a temporary attitude adjustment. If that makes a difference, look for a new cluster.

#4

The cluster is a good place to look also, forgot that one. And even just the SI board. Had a bad one with my build. Got to love parts cars.

Michael
#36
Great Lakes Region

#5

A common problem with the fuel and temp gauges is deformation of the solder pads and the resulting poor contact where the gauges bolt to the main PCB in the cluster. The fix is to disassemble the cluster and re-flow solder on those pads. Also, there’s a ground point for the cluster under the dash that can be a problem.

On late model cars (9/87 and later) a bad connection at C191 (under the intake manifold) and cause problems with the temp gauge (and injectors and DME temp)