I've decided to start a new thread, because the overheating problem has been resolved, but now I can't figure out what is wrong with the analolg coolant temp gauge.

Here's the orginal thread if you want to follow from the beginning. http://forums.corvetteforum.com/zerothread?id=635557

Here's where I left off with the last thread:
I pulled the ECM codes and came up with a code 28, which if I'm reading it correctly, says the fan relay was most likely at fault, which makes sense because after replacing it the engine has not overheated. The rad cap that was there before was also not the right size and I did replace that as well.

MY problem now lies in that the digital temp gauge and the analog temp gauge do not match. I replaced the coolant sensor for the analog gauge (boy was that a pain), but the analog guage still goes all the way to the max(260) while the digital gauge never goes above 220 after 30 minutes of idling. But if I turn the AC on the analog guage will come down, but still doesn't match the digital gauge - the digital guage will read about 195 and the analog will read around 220 (those readings were also the case with the AC off)

Now I've heard others say the analog gauge isn't all that accurate, but can it really be that far off? Is it realistic to think the analog guage will read accurately after 30 minutes of idling? Anyone got any ideas??

Anyone ever hear of the gauge itself in the instrument panel going bad? If so any ideas what it would take/cost to fix it?

I offer my much appreciated THANKS in advance!

 

The analog temp guage in my 94 is way off also. I have just learned to ignore it. I know that is not the answer you want, but the fact is, it is not worth the time and $ to me to fix it (if I could even figure out how). Whenever I want a temp reading, I just go to the digital guage.

 

Not to steal the thread, but I have been following your plight with intrest 'cause my 91 has had the same problems. You mention both analog and digital gauges, did yours come with both or did you add a digital gauge?

 

I thought I read that 92 on up has both, mine is a 93 LT1 and has both

 

You are aware that the analog gauge is not linear.

On a '96, here's the breakdown for the markings on the analog gauge.

1st mark(left) is 100 degrees,2nd mark is 185,3rd is 210,4th is 235 and the last is 260.

For normal operation, your needle should be between the 2nd and 3rd mark(closer to the 3rd).

 

I kinda of figured it wasn't exact, but even so, my digital will read 220 and the analog will be maxed out at 260, but am I skewing these results because, I'm not operating at normal driving conditions, i.e parked, just idling for 30+ minutes?

 

Correct, the digital coolant and oil temp readouts didn't come until '92's.

I don't have my service manuals with me (at work), but the only thing I can come up with off the top of my head is since there are two sensors at two locations for the analog and digital gauges, one of two things could be amis:
1. There is a blockage or an air bubble in the coolant passages and it's causing the temp to skyrocket near the analog sending unit. That's not good in any case. I'd try to burp the system just to make sure.

2. It's possible the sending unit and/or the connector and wiring are corroded. I don't know if the resistance of the thermocouple goes up or down relative to the temprature though. If it's proportional (resistance goes up with temprature), then some added circuit resistance could be skewing the reading.

 

Shawn,

quote:
--------------------------------------------------------------------------------
1. There is a blockage or an air bubble in the coolant passages and it's causing the temp to skyrocket near the analog sending unit. That's not good in any case. I'd try to burp the system just to make sure.
--------------------------------------------------------------------------------

Is burping the same as bleeding? If not would you mind explaining?

 

Well, the way I "burped" my system was to fill the radiator resiviour all of the way up, start the car, add mix as the level went down, then wait for the engine to warm up enough for the thermostat to open (you should see the level drop a little more then).
Make sure your overflow tank is at least 1/3 full (to avoid the system sucking in air later).

When everything is up to operating temp, have someone bring the RPM's up to about 2500 RPM and hold it there. Add enough coolant mix to the upper tank to fill it to the brim. Cap it then have the other person let off the gas.

 

Hey Mr. Mojo,

Quote:
------------------------------------------------------------------------------------------
For normal operation, your needle should be between the 2nd and 3rd mark(closer to the 3rd).

------------------------------------------------------------------------------------------

I take it just having it idle for 30 minutes is not considered "normal operation", but it still shouldn't max out, right?

We'll take it out on the road tonight and see what happens.

 

Nick, correct, idling for 30 minutes isn't normal. Both my cars will see about 195-210 under normal driving conditions on the highway. Around town slightly higher and sitting in traffic it will get as high as 230. All perfectly normal.

If you are seeing 260 on the analog I would guess that there is something wrong such as the sensor.

Usually when you reach the danger zone, the "check gauges" will light up on the dash.

 

Unbelievable! For the two months I've had the car, I've been really fretting about the fact that the analog temp guage never gets under 210 and sometimes goes as high as 240. I was all set to pull the radiator, install a new thermostat, flush the system, blah blah blah and then I read this thread. I had NO idea there was even a digital guage. Yeah, I toggled through them all once while I was waiting at a stoplight or something but I didn't really pay any attention. I just leave it on the MPH/odometer readout. I took the car out this evening and sitting at a railroad crossing for ten minutes the digital temp never got above 204 while the analog was indicating 235. I've been JUST waiting for the car to overheat, looking underneath it for coolant puddles every time I park the thing. What a goof...
:bb :bb :bb

 

Hey Frank, thanks for the info. I did change the sensor, but still no change in the guage. I believe Shawn mentioned it could be fautly wiring. I think I'll try pulling the rad and looking for debris and while I'm at it flush it out and see what that does. If that doesn't help, then I'm done. As long as the digital works OK, I'm happy with that for now.

And John, don't feel so bad I was the same way. When I got the vette a couple months ago, I was like a kid in a toy store touching all the buttons, I saw the various digital gauges, but it didn't register in my brain again until someone reminded here. I guess I can use the excuse of turning 40 in a couple of weeks. LOL

 

NickM wrote:
"...If that doesn't help, then I'm done. As long as the digital works OK, I'm happy with that for now"

Well, my analog seems to be way off as well. I've got an extended warranty so I'll let the dealer figure it out. If you can wait about a month for an answer (there's a couple other things on the car that need attention and I'm trying to consolidate everything into one service trip), I'll let you know what the dealer did to resolve it. It might save you some time and aggravation...