I can't say that the Lectric Limited sender is not your problem...only that lots of folks on this Forum have pitched senders they got from other vendors (which did not work properly) and were very happy that their new senders provided reasonably accurate readings. Is there a possibility that the gauge in your car has been replaced as well? Through the build years of the C3, the sender calibration and the gauge calibration were altered [by design], so that the mixture of gauges for certain years and senders for other years have created a bit of a problem.

If you have a sender that functions (approximately linear change in the "resistance/deg. F" throughout the working temperature range) and a gauge that functions (ditto), they can be calibrated to work properly with each other...even though they weren't a "set" to begin with. It would take a little calibration work to determine what resistance the gauge wants to 'see' at temps of 100F, 150F, 200F, and 300F; then determining the actual resistance provided by the sender for those same temperatures. A simple resistance circuit could be designed and placed between the sender output pin and the sender wire to recalibrate that circuit. It would probably not require more than 3 resistors (worth about 25 cents each).

Now, ask me why the folks who sell you this stuff haven't already done that and included the "correction device" to make the sender and/or gauge work properly with the mating device you presently have... Answer: It would take a couple of hours to figure out how the parts they are selling perform [from an engineering perspective] and a couple of bucks each for supplies and labor to make up a simple "correction device". Of course, they could explain that you needed that device and have you pay 10-20 times what it is worth. But, that's their game. Instead, they just sell you what they have [even though they don't really know how the device is calibrated] and let you deal with the fallout.

 

Good points made. A handfull of resistors at .25 and try to get a matching set of gauge, resistor and sendor unit. If this is a project one wants to get into - what range of resistors do you think would be needed?
I have an IR gun so taking actual temps on the block and radiator is not a problem. I also have a mechanical gauge in the other head so I get real time readings of temps. Thx

 

If you go to Radio Shack, you can buy five (5) 47 ohm resistors for $1. With those resistors, you can combine them into the following {approximate} resistor values: [series connected]: 100, 150, 200, 250; [parallel connected]: 25, 16, 12, 10. So, once you stick your sending unit in a pot of water on the kitchen range with your ohmeter hooked up to it (one lead on output terminal and one lead to the metal case), you can put a kitchen thermometer in with it and start turning up the heat to 100F, 150F, 200F and 212F [boiling]. Record the sender's resistance at each of those temps.

Then work on the gauge calibration. With ignition ON {engine OFF}, install a resistor between the engine block (electrical ground) and the sender wire; then take a gauge reading. Try different resistor combinations until you determine the resistances it takes to get readings of {approximately} 100F, 150F, 200F and 250F. Once you get that data, send it to me in a PM and I'll calculate exactly what the "recalibration system" of resistors needs to be for your car. I'll return that info in a PM and/or start another thread on this to offer such a solution for others.

7T1vette

 

Remember if you are using resistors between the gauge and sender (green wire side) you can only make the gauge read COLDER.

 

Hi Guys
Just reading thru this thead as i seen to have the same problem with my 68 bb the temp reads about 120 however when i put a ir gun on the stat housing it read about 220 when i earthed the green wire the gauge only read about 250 shoudn't the gauge hav gone to 280/max any thoughts would be appreciated

 

What does the gauge do when you unplug the sender wire ?

 

FWIW...

I had a longer drive this weekend in warmer weather, it seems that in the warmer ranges, the Lectric Limited sensors is closer to accurate then I thought. At the cooler side of the temp range, say 160* or less, the factory gauge still reads a little too cool...but when my mechanical gauge is in the 185-188* range, my factory gauge is reading dead on the middle mark(line between 100 and 210)....at 205* on my mechanical gauge, my factory gauge is reading about the same(the best I can tell)....mine never got to 210 but if it did, I think the gauges would match exactly.....

All that being said...I am still keeping my mechanical gauge in the car so I can keep close tabs on the temps, particularly in the 160-190* range...

So I stand corrected on the Lectric Limited switch....

 

With the wire unpluged it reads just under the 100 mark on the gauge