1994 Coupe -

I have had this car for many years now and the analog temperature gage generally displays a little hotter than the digital. I typically have the digital temperature gage displayed at all times due to the fact that the car has always run hot, especially in traffic. I will hit the 220 to 230 range at idle if I am not running a/c fans.

I have replaced the radiator, thermostat, hoses, flushed, etc. In my opinion, the car just runs hot. Previous posts has resulted in many opinions on this ranging from 'that is normal' to 'your car is running hot', etc. Feedback welcome on that issue......however...... that is not the point of this post.

Recently, I have noticed that the analog gage is substantially higher than the digital. I means SUBSTANTIALLY.....to the point that I do not believe it. For example, with digital at 200 deg (most common temperature when driving on highway), the analog was reading 235 (I have never had that high of a delta before).

So, I came home and let it sit at idle with a/c off (fans off) and let the digital climb to 230 degrees (which it has always done at idle) until the fans kicked it. By the time I got to 210 or 215, the analog was pegged!

Driving the car later that day, it seem to correct itself and both gages were back to being the same temp (with the analog always a little higher).

Then I went back out later and drove it again and the analog went back to reading significantly higher again.

So, has anyone had this experience?

Any suggestions on either issues.

1. Temp always goes up to 230 at idle (a/c off, or fans off)

2. Large discrepancy between gages.

As always, thanks for taking the time to read and respond.

kc

 

I believe the C68 readout uses the ECM information that is supplied by the TCS at the water pump housing. I'd either check the temp sender for gage using a DMM and see if that reports a matching value that the cluster gage is reporting. I don't know that there are values in the FSM for your year but generally something at or near 1400 ohm is considered 100* or cold when allowed to cool maybe over night and something near 145 ohm is considered 220*. There's a wide range of +/- involved but it's maybe worth a check OR just replace the gage sender right side of the engine I believe.

 

I looked thru the 94 FSM and could not find a chart for temp vs. resistance for the sensor that drives the analog dash gauge. I would basically check to make sure the wire to the sensor is not shorting to ground or insulation rubbed away making a high resistance ground connection.

Other than that there is not much to the circuit. Gauge gets 12 volts and ground, and input from the sensor. I assume all other analog gauges are working OK. Probably the easiest way and first step to resolve the problem is to replace the sensor in the head.

 

In the FSM it mentions putting 1400 ohm to the gage and it should go cold and I believe they mention 55 goes to hot. GM used a variable load device to check all gages in clusters, I used some information from Wells for their TSU that mention 100 & 220 but like I mentioned there were big +/- variables noted in their specs.

Try 8A-82-11 Chart #9

 

Excellent find, I do see it.
It looks like the sensor has a negative temperature coefficient. So if the wire grounds out, the gauge should go hot.

As you said, the tolerances of what a cold and hot indication is seems subjective.