Tweet
The temp gauge on my '62 is not reading accurately. I recently rebuilt the motor, but once the car was put back together, the temp gauge started reading too high. I know that the engine is not running hot, but the gauge is showing 220 - 240 degrees. Has anyone had a similar problem? Could my sending unit be bad? Could I have a ground problem? Does anyone have any suggestions?
-
-
Re: C-1 Temp Gauge False Reading
John - I am assuming that you DIDN'T change your sending unit as part of the rebuild based on your comments...is that true? Most of the current senders read too hot. There are many posts here (search the archives) about this topic...you should see around 700 ohms resistance at room temperature if I recall....I would start by checking the impedance of the sender as step 1....Craig -
Re: C-1 Temp Gauge False Reading
Craig, I did not change the sending unit at rebuild. Sending unit reads 680 ohms at room temp. Do you know the readings at various temps? What should it read at 160, 180, 210 etc? I will search the archives. Thanks.Comment
-
Re: C-1 Temp Gauge False Reading
John,
According to the research by Dwight Farmer in the Corvette Reastorer Vol 16 #2
the following resistance and temparatures as follow
Temp Ohm reading
(F)
75 700
140 260
160 180
180 150
200 120
Regards,
Donald #31176Comment
-
Re: C-1 Temp Gauge False Reading
John, I honestly don't recall the complete graph of temperature vs impedance. However, 680 sounds in the ballpark. Was then engine bored out much? I know SB's tend to run hot after overbores....this may or may not be related to or aggrevating your problem. Do you know if your radiator is in good condition as far as thermal transfer...maybe it just can't keep up with the cooling. My 67 L79 tends to run hot, it is 0.030 over, and I have a new Dewitt's radiator ready to go in as the old 72 date code Harrison is just not hacking it any longer. You may have aggrevated a marginal radiator with the rebuild...just a thought...CraigComment
-
Re: C-1 Temp Gauge False Reading
Most senders that read about 700 ohms at room temp will give fairly accurate readings. The problem you describe is a classic "bad sender" symptom, but if the sender was good prior to rebuild that may not be the case. Did you R&I the sender from the manifold? If so, did you use any type of thread sealer? This usually results in the opposite problem, but the question is worth asking. The first thing I would do is validate the actual engine temp with an IR thermometer aimed at the base of the thermostat housing. If indeed there is a discrepancy, I would next run a temporary wire from the sender to the gauge and eliminate the wiring. If that checks out ok, I would remove the sender and check the resistance again. At that point, I would probably change the sender to a Wells TU5 ($6 at Autozone) and see if that made a difference. If you still get a false reading, you will probably need to send the gauge and the sender to someone to calibrate them as a matched set. I have a suspicion that your sender is faulty, even though it reads correctly at room temp. Only real way to validate that is to change senders.Comment
-
Re: C-1 Temp Gauge False Reading
I had the identical situation with my '62. Tried several different temp senders, all read too hot. Finally got a good one from Mary Jo Rohner. VetteGal.com. Good luck , Art.Comment
-
Re: C-1 Temp Gauge False Reading
In 1990 I wrote the article for SACE explaining the early sender and why owners needed to locate an old one and not buy the replacement.They DO go bad, find an early 56 and up CAR sender. Or Chevy World Int. will have them.Comment
-
Re: C-1 Temp Gauge False Reading
Thanks for your responses. You have all got me going in the right direction.Should be an easy problem to resolve now. Again, Thank to all who have responded.Comment
-
Re: C-1 Temp Gauge False Reading
Roy, do you have a phone # or E-mail address to get in touch with Chevy World.Comment
-
Re: C-1 Temp Gauge False Reading
Check the heat riser make sure it's opening.Comment
-
Re: C-1 Temp Gauge False Reading John
www.classicchevy.comComment
-
Re: C-1 Temp Gauge False Reading
I had a problem simalar to yours and I found the ground to the gauge wasn't the best. When my headlamps were on the gauge went even higher. The car must have been trying to ground through the unit ?Comment
-
Some advice may be a myth...
Most everyone knows the 'formula' for temp senders has changed over time along with their physical packaging--what marks appear on the case, and so forth. I've gathered maybe, 200, original temp senders from scrapyard cars over time and I've seen just about every variation in construction, case marking/emboss, and resistance profile that's possible.
Of course it's the resistance profile of the part that's important to getting a proper reading on the dashboard gauge, but that's only part of the picture. For the 'system' to report temperature accurately, the SYSTEM must be intact. That means good electrical contact(s), a proper starting voltage (combination of alt/gen and voltage regulator) and an in-dash temp gauge that retains its factory original calibration. The later is often overlooked....
We routinely send instrument clusters out to be 'restored' (electrically, mechanically and cosmetically) and almost NEVER question the restorer's technique for cosmetic refurb. I simply don't know how one can freshen the silk screen on a gauge face without removing a guage pointer needle.... When this is done, kiss the factory original calibration of the guage good bye!
Since the response of the temp sender is non-linear and the gauge face is detailed to 'linearize' the response with gradacules placed where they are, getting things back together 'close' to original doesn't cut it. You have to be on the money AND know WHERE factory original accuracy was specified (hint: it's NOT in the center of the dial--'typical' engine temperature conditions).
I also hear comments about how a 'good' temp sender ought to measure 700 ohms at room temperature (typical definition is 68F). While this 'could be' in the factory original loci for an AC 1513321 sender, it's not part of the sender's factory spec. It's not a matter of resistance at ONE temperature--it's an issue of the guage being correctly calibrated, the electrical 'nest' being intact, and a temp sender with correct, factory original resistance vs. temperature response curve SLOPE being there....
For those wanting to better understand the 'mystery' of sender, gauge, and 'nest', the article I wrote on this subject for the Rocky Mountain Chapter Newsletter last September might help. If you have Adobe Reader, it's a FREE download and you'll see REAL numbers vs. reverse engineering speculation on what's right. Just wander over to:
www.NCRSRMC.org/Downloads/Sept-2002-Newsletter.pdfComment
Comment