Is there a cooling sending unit that has proper calibration available? I have problems with the temp gauge on older Corvettes indicating much hotter temps than actually exist. I have tried GM senders, napa senders, Niehoff senders with no success. The only thing that works is to find an original sender from a 50's or 60's engine. My local supply is getting thin. Any Ideas? Casey
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Re: overheated in Idaho
In absolute desperation, you could use an original sending unit as a baseline, heat it in a jar of water to the engine's thermostat temp, and measure the sending unit's resistance at thet temp. Since the newer units tend to have lower resistance, you could then purchase a new sending unit, test the new init the same way at your ecpected thermostat open temp, and use a fixed resistor hiddedn in the loom to adjust. It won't be perfect, but at least it will be accurate at normal op temp and if it goes up you'll know it's a real problem. Otherwise, look beyond Chevrolets in your search for a good sender. Other GM's used the same item. -
Re: overheated in Idaho
To all,
There is an article on this subject in the next Restorer which is being printed now. Basically it is how to add a resistor to the circuit. Have a little patience and one solution will be in your mail box.
Terry
TerryComment
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Re: overheated in Idaho
I've heard of a method of correcting the accuracy of the gauge by adding some resistance in series with the gauge. This lowers the overall current in the circuit at any given temperature, thus making the gauge read lower.
However, there is a problem with this method. At a given temperature, most gauges require a LOWER resistance than the sender will provide. Adding resistance in series will only make the overall resistance HIGHER.
You can, however, add some resistance in parallel with the sender to make the gauge see a lower overall resistance. This technique will work, however, it adds non-linearity to an already non-linear gauge-sender system. Does the additional non-linearity cause a problem? Probably not. It all depends on the specific numbers.
I'm looking forward to reading the article. Hopefully, it will address some of these issues. IMHO, the best way to calibrate the gauge sender pair is to calibrate the gauge to the sender, and not the other way around. This has the disadvantage of having to remove the gauge from the car.
My data comes from making measurements on at least 20 midyear temperature gauges, 10 original senders (some NOS) and 20 replacement senders. Ironically, the only gauge that would benefit from a series resistor in the circuit is the one on my car!Comment
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Re: overheated in Idaho
Fred, How difficult is it to calibrate the temperature guage to a specific sending unit, specifically is there a needle adjustment on the guage itself, does one need to disassemble the temperature guage to access an adjustment screw? My instrument cluster is currently taken apart. I have no idea if the guage is accurate or not. I suppose a simple bench top circuit, hot water and a thermometer for reference would be the starting requirements. Thanks, Scott MarzahlComment
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Re: overheated in Idaho
Scott,
Unfortunately, there is no screw you can turn to calibrate the gauge or sender. You need to take stuff apart. You can, however, use a bench setup with a pot of hot water to check the calibration of the gauge/sender. You need a good lap type supply to do this.
The other thing you can do to check the calibration with the system in the car is to use an infrared thermometer. You can buy them for as low as $150 these days. Measure the temperature around the sender. It should match with what the gauge reads.
Hope this helps.Comment
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