Does anyone know the resistance values of the temp sending unit at 100, 210, and 250 F. I would like to make sure I have the pointer in the correct place BEFORE I put the cluster back in the car. Thanks.
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Re: Water Temperature sending unit resistance
I bought a new sender, pirated the Autometer mechanical temp gauge off my 66 Nove Super Gasser (I broke it a couple of weedends ago bad) and got out my Fluke meter I have the numbers from 80 to 212. If anyone wants them, e-mail me and I'll send them along via e-mail. I don't want to clutter up the board with a bunch of numbers. -
Re: Water Temperature sending unit resistance
Question is too complex to answer as enumerated....
First, temp sending unit was NOT a static component. There were numerous engineering changes to temp vs. resistance non-linear response curve over time. So, first question refinement deals with what year car/gauge/sender you're asking about.
Second, sending units were NOT spec'd with a transfer function. AC drawing consisted of upper/lower bounded loci for response curve allowing a RANGE of acceptable T vs. R transfer functions. The delta between upper/lower loci was NOT constant, very wide at low temperatures and narrowed CONSIDERABLY at high temperatures.
Third, when temp gauges were calibrated (process varied with model year), accuracy was pegged at the HIGH end of the gauge vs. mid-range or 'typical' engine temp values. So, trying to make a given gauge accurate across the board by selecting ONLY a temp sender could well be an exercise in squeezing on a balloon! Looks to me like designers were more interested in making the temp reporting system accurate at/near the point of critical engine overheat (threat to life/limb/property) than they were in delivering an engine thermometer with an accurate dynamic range.
Last, some may tell you they've got the 'secret' for this/that number, but unless they can show you the AC-Delco temp sender drawing side by side with the AC-Delco guage drawing they may well be blowing smoke....Comment
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Re: Water Temperature sending unit resistance
Jack- You are quite right. The test I did had bounds of 569 ohms at 75 F and 27 ohms at 250 F. The slope of the curve between 75 and 140 is -5.95 ohms/F from 140 to 250 the slope is -1.4 ohms/F. I have the complete table for this sending unit if you want it. It is GM 12334869, fitting 56-78 cars. It would be interesting to test several units, but not at 15 bucks a pop, plus what would I do with all those sending units. Thanks for the help.Comment
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Re: Water Temperature sending unit resistance *TL*
wrb,
Please check your e-mail address. I keep getting bounced messages from the e-mail notification of responses checkbox.
To everyone else: Please check that YOUR e-mail address is correct if you have the e-mail notification box checked. If you visit the board often and don't really need to be notified uncheck that box and save some system resources. You would not believe how many bounced messages land in my e-mail box each day.
Give me a break.
John
Administrator
www.ncrs.orgComment
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Re: Water Temperature sending unit resistance
I did test several (many) temp senders & can verify that there is a significant range of R values at a given temperature. For the reasons Jack mentions, the gauge-sender combo was never designed to provide lab grade accuracy. The system uses a thermister, which is highly non-linear & hard to control the tolorances closely for accurate measurements. The reason for the non-linear graduations on the gauge face is to compensate for the non-linearity of the thermister in the sender. GM used this system for one reason -- it's cheap.
With this said, there is an alternative. Since you have the gauge out of the car, I'd set up the gauge & sender on a bench. Use a pot of hot water with a thermomecter & insert the sender into the water. You can now make the temperature of most interest read 'accurately' by adjusting the needle on the gauge. The caveat here is that you're simply moving the inaccuracy to another part of the gauge dial.
One thing that I've noticed about other GM muscle cars with gauge packages is that temp gauges do NOT have numbers on the dial -- at least the ones I've observed (Camaro, GTO, etc.) I now understand why.
Fred OComment
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