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This is like 'dancing'...it takes two to tango... We tend very quickly to lay 'blame' to the temp sender when we see inaccurate readings displayed on the dash. A little understanding goes a long way!
First, there's early and late style temp gauges. Each was built WITHOUT the pointer needle installed and sent to final test/calibration. The early gauges were connected to a 'ding ding' box that emulated 'worst case' conditions (car in motion, engine about to overheat) and the final assy operator installed the pointer needle to a prescribed position (tolerance defined) at the TOP OF THE DIAL. Nobody gave a 'hoot' about a given gauge's mid-range accuracy profile (is 180F really 180F or might it be 191F...that was beyond the scope of the measuring system's accuracy profile).
Second, later temp gauges were built and send for final test/cal with the pointer needle 'loosely' installed based on 'cold' conditions. At final test, each guage was connected to a 'ding ding' box and electrical power was applied to force a legitimate engine overheat condition. The assy operator looked at were the pointer needle was actually driven and and hand selected a precision wire wound calibration resistor to install as a 'shunt' onto the gauge to force it point to the proper place at the HIGH END of the dial. Again, nobody gave a 'hoot' about how accurate the gauge was in its mid-range.
The big picture is the temp reporting system was sloppy and inaccurate UNLESS there was a bona fide high end of the dial engine overheating condition threatening! BUT, we continue to use a big hammer to try and FORCE these antique cars to act like today's Swiss watch instrumentation. Yes, it CAN be done, but you have to hand verify the temp gauge and then hand match it to a temp sender (there was a WIDE degree of variance on what was an 'acceptable' temp sender even back then).
What you can't do is (1) presume your dash gauge is 100% correct and (2) go looking for that 'magic' temp sender that makes it accurate ALL the way across the dial from 100F to +240F. If you take that approach, you're banging your head against the wall because that wasn't the way things were back then!
Last, understand if you can't say with absolute certainty that your temp gauge has NEVER been out of the instrument cluster since the car left the factory, AND it's never been electrically overstressed, then you HAVE to presume there's some degree of inaccuracy in the gauge and probably another degree of inaccuracy in the temp sender and you can't get from here to there without addressing both sides of the equation at the same time!
I've yet to see a source in the instrument restoration business take a bold face claim that they 100% restore to factory original specs! What I'm getting at is this:
There's no way you can re-silk screen the face of a temp guage without pulling the pointer needle. ONCE, you do that, kiss the factory original calibration of the guage bye bye!!! So, the fact that this/that guage went out to this/that restoration service for overhaul doesn't mean diddly in my book. The fact that you've acquired this/that temp sender and installed it is equally faulty logic.
To get from here to there, you need to verify the gauge behaves as designed over a range of voltages and current flows AND the temp sender behaves as designed over a range of temperatures and equivalent resistance values. If you do one without the other, it's like dancing the Tango by yourself...
First, there's early and late style temp gauges. Each was built WITHOUT the pointer needle installed and sent to final test/calibration. The early gauges were connected to a 'ding ding' box that emulated 'worst case' conditions (car in motion, engine about to overheat) and the final assy operator installed the pointer needle to a prescribed position (tolerance defined) at the TOP OF THE DIAL. Nobody gave a 'hoot' about a given gauge's mid-range accuracy profile (is 180F really 180F or might it be 191F...that was beyond the scope of the measuring system's accuracy profile).
Second, later temp gauges were built and send for final test/cal with the pointer needle 'loosely' installed based on 'cold' conditions. At final test, each guage was connected to a 'ding ding' box and electrical power was applied to force a legitimate engine overheat condition. The assy operator looked at were the pointer needle was actually driven and and hand selected a precision wire wound calibration resistor to install as a 'shunt' onto the gauge to force it point to the proper place at the HIGH END of the dial. Again, nobody gave a 'hoot' about how accurate the gauge was in its mid-range.
The big picture is the temp reporting system was sloppy and inaccurate UNLESS there was a bona fide high end of the dial engine overheating condition threatening! BUT, we continue to use a big hammer to try and FORCE these antique cars to act like today's Swiss watch instrumentation. Yes, it CAN be done, but you have to hand verify the temp gauge and then hand match it to a temp sender (there was a WIDE degree of variance on what was an 'acceptable' temp sender even back then).
What you can't do is (1) presume your dash gauge is 100% correct and (2) go looking for that 'magic' temp sender that makes it accurate ALL the way across the dial from 100F to +240F. If you take that approach, you're banging your head against the wall because that wasn't the way things were back then!
Last, understand if you can't say with absolute certainty that your temp gauge has NEVER been out of the instrument cluster since the car left the factory, AND it's never been electrically overstressed, then you HAVE to presume there's some degree of inaccuracy in the gauge and probably another degree of inaccuracy in the temp sender and you can't get from here to there without addressing both sides of the equation at the same time!
I've yet to see a source in the instrument restoration business take a bold face claim that they 100% restore to factory original specs! What I'm getting at is this:
There's no way you can re-silk screen the face of a temp guage without pulling the pointer needle. ONCE, you do that, kiss the factory original calibration of the guage bye bye!!! So, the fact that this/that guage went out to this/that restoration service for overhaul doesn't mean diddly in my book. The fact that you've acquired this/that temp sender and installed it is equally faulty logic.
To get from here to there, you need to verify the gauge behaves as designed over a range of voltages and current flows AND the temp sender behaves as designed over a range of temperatures and equivalent resistance values. If you do one without the other, it's like dancing the Tango by yourself...
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