Hi,

It's been awhile but my 1990 Corvette is back on the road. It blew a head gasket over three years ago and I decided to rebuild the engine. It took awhile due to some unforeseen circumstances but now it it complete. There are just a few problems that I don't recall being an issue before the rebuild. One is that the temperature gauge is reading wrong. I compare the gauge readings with actual temperature from the sensor feeding the ECM (doing the resistance to temperature conversion outlined in the repair manual) to the gauge in the dash and it reads OK up to about mid gauge. But then when the dash gauge reads 260 or in the red zone, the resistance from the ECM sensor indicated a temperature of only 220 degrees. Of course, this was freaking me out thinking that I was overheating the engine. But I confirmed this with a IR temperature gun. Above half way on the temperature gauge, it reads proportionally high until it maxes out, and at that point the actual temp is still only 220 - 230 degrees.

I have read a lot about increased resistance in the temperature gauge circuit being the culprit, but this, if I am correct in my thinking would lead to lower than actual temperatures instead of higher temperatures. Therefore I am wonder what else might be responsible for the incorrect gauge readings. I have replaced the gauge sensor on the passenger side cylinder head when I rebuilt the engine.

Any help appreciated. Thanks.

Mike

 

Hey, No comments on this issue? Am I the only one with this problem?

 

Hi
The temp sensor will give a wrong reading if the engine was overheated.
It happened to my vette blew a hose. Was fine when i replaced the temp sensor on drivers side of engine.

 

Happening to me right now, in-car gauge reads 10-15F higher than the CTS on the front of the motor. I was looking in the manual to figure it out yesterday, and havent yet.

I replaced both sensors with the new engine, and now a brand new one reads 10-15F high, when it read perfectly before with the old sensor in the old engine....so I dont think its the resistance of any wires.

 

It appears most of the auto part stores sell a generic replacement sender/sensor. One part fits many vehicles.

For a 90 L98 Corvette.

The part number in the Chevrolet microfiche says to use a
Delco D1885 or GM 8993146. This has the single push on
spade lug connector.

If you have the side slide on type connector use a
Delco 213-80 or GM 25037346.

 

Mine does the same thing. Before the tune, fans would come on as requested at 238*, even though it showed 260 on the analog guage on my 91.

Now when it runs at 180* the guage is not in the middle like it should be.

Also, my oil temp guage is junk, and its in the cluster. Everything reads correct on tunerpro.

I think it is time for a Cluster rebuild but as long as I know whats up, all is fine.

 

Same problem in the '93 I just put back on the road ....
Coming home in traffic, the analog gauge almost hit 260*, which scared the crap out of me ..
But, after reading a few posts on here. I started it in the driveway and let it run, bringing the digital gauge up on the dash display and comparing the two ...
The analog gauge actually showed a cooler temp until about the hal-way hash-mark .... after that, it started to read hotter than the digital gauge.
Again, with the analog gauge reading almost 260*, the digital gauge read in the mid-high 220's .... and then, like clock-work, at 228* the fan kicked in and it colled down to 215* ...
Of course, my '93 is an LT1 and your '90 is a Tuned-Port, but I believe similar conclusions can be drawn about the correctness of the analog gauge readings ...

 

same problem here after the mechanic installed the new heads and cam, my gauge was working perfectly before of that, i tried switching the sensor to the driver side, same thing, was reading 260 when it actually was 220!!

 

Folks,

Thanks for your help. I am re-energized to solve this problem.

Mike

 

Mike !!!
Just through away any aftermarket temp sensor if u have any in ur car and get the oem one from the dealer, that's what I did after going through 2 aftermarket temp sensors and my gauge was still over reading, now with the oem sensor my gauge seems to be sworn to say the truth only and nothing but the truth!!! Lol
Ricky

 

I just noticed and posted about this issue today. If your 86 is wired like my 89, the dash guage measures temp from the sensor by the dipstick. The ECM uses the sensor under the stat housing. Mine are about that far apart too. And, apparently, there's a reason for it.....

That reason was posted by JFB explaining why he thinks there's a difference in temp at the two sensor locations.

 

Well it's easy to find out the sensor that is sending to the dash by simply grounding It to the block and having somebody watch the dash with the ignition on, on my 91, I have the sensor by the dipstick too, but grounding the wire that goes to the sensor In the head makes the gauge move

 

Folks,

I just replaced the aftermarket temp sensor (from Checker) with a OEM sensor from AC Delco. This fixed my problem. For reference, it was the sensor located by the dipstick. Wow, I am blown away. If you cannot have confidence in a new sensor from an auto parts store, what is this world coming to? I must have over 20 hours in that problem.

Thanks again for all your help.

 

i told you!!
i was surprised from the result too!! i was thinking of buying a new dash for my car when i had this problem!, i even installed a mecanical gauge on the driver side head just to be able to see the corect temp!!
so thats mean when it comes to sensors,,,,, go oem only always

 

unfortunately "new" doesn't always mean "good"

glad you got it all figured out.
In the future - assuming the temp sensor isn't the problem:
When the cluster temp gauge gives a false reading of being way toohigh (299)it means the sensor is not grounded well/at all (or the harness/connector is loose and/or electrically disconnected). If the cluster temp gauge gives a false reading of being way too low then the circuit is effectively shorted out to ground.

 

Let's hope we will never get there!!! Replacing the sensor sounds away easier than that!!