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After trying 4 different sending units, I have come to the conclusion my temo guage isn't calibrated correctly (although supposedly refurbished by a reputable shop) Somewhere I recently saw advertised an adjustable in line resistance gismo that could be hiden under the dash (car not to be judged). Can anybody steer me to a supply source for one of these devices? Thanks in advance, Bob.
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Re: 57 temperature gauge
How far off is your gauge? Using a resistor to trim the temp to a mid scale reading may in some cases render the gauge useless at higher temps and it may not warn you of an overheat situation. Obviously a frustrating problem, but these gauges CAN be made to work fairly reliably. What kind of sending units are you using? -
Re: 57 temperature gauge
Bob,
Make sure you dash gauges are well grounded and all other copper braided grounds are installed properly Had a similar problem with my 57. I found the ground wire loose. You didn't by any chance use Vette clocks by Rodger to do the calibration??Comment
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Re: 57 temperature gauge
I had similar problems with the temperature gauge in my '56, would read hot all the time when the IR gun would indicate a normal temperature of 180 degree. I purchased a potentiometer at Radioshack and determined that I needed (in my case) a 22 ohm resistor for accurate reading at 180 degree. The temperature readings at below and above 180 would not 100% accurate, but wouldn't be that far off either.
Pierre G. Joly #34410Comment
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Re: 57 temperature gauge
I have tried the Wells TU5 and most recently the one thats supposed to calibrate from Lectric limited. By the way all wiring is new (Lectric limited) and all grounds are good. Last sending unit was installed without any thread dressing. I can't remeber where I saw the resistance gizmo, I have a hard time remembering names, but the name Roger does seem familiar. I have checked engine operating temp with IR gun and all is OK, but would like to be able to detect relative changes while driving, so I think the gizmo would be OK.
As usual, thanks for your help.
BobComment
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Factory original temp gauge cal....
was done by assy folks. Method was pretty simple and you CAN do it yourself.
Finished gauge (less pointer needle) was placed in a precision fixture that supplied regulated voltage and a fixed, precision resistance to ground to mimic conditions seen at the start of engine overheat (approximately 240F). Then, the final assy worker pushed the needle pointer onto the shaft making it point to this high end of the gauge position. Specified accuracy in installing the pointer needle was something like +/- 8 degrees (this is another source of gauge mid-range, normal engine temp, display error).
You see, the allowable variance in sender resistance with temperature is non-linear AND the variance changes with temperature (wide and sloppy 'accept' range at low temps and tight/narrow range of variance at the high end of the dial; 240-260F range). The spec on the temp sender being what it is, says designers weren't really concerned with highly accurate temp reporting under mid-range, normal driving conditions--they wanted the system to be accurate where it counted (bona fide engine overheat situations).
Later temp gauges (late Mid-Year and Shark era) were calibrated a bit differently. The same kind of precision fixture was used, but instead of pressing the pointer needle onto the gauge shaft the final assy operator installed a hand selected, precision, wire wound shunt resistor onto the back of the gauge to 'trim' it into calibration.
You can duplicate the factory's calibration of the gauge yourself. Go get the article I wrote from the Rocky Mountain Chapter website (www.ncrsrmc.org; Sept-Oct 2002 Newsletter) where the original AC spec on the sender is shown. Pull your temp gauge and look for a gradicule marking at the high end (235, 240, 250, Etc. per your particular gauge). Run down the temp sender response curve to find the allowable resistance range for that temp.
Now, either turn and fix a potentiameter or make up a fixed resistor (1/2-watt works) to emulate the high end temp mark on your gauge. CAREFULLY, pull the pointer needle from the shaft, and connect the gauge to a bench supply (13.8 VDC works nicely), through the resistor/potentiameter to ground. The pointer shaft will swivel to position. Now, press the indicator needle back onto the shaft making it point to the proper temp mark on the gauge face. You're DONE--the gauge is properly calibrated!
T******* the temp sender with external series/parallel resistance to FORCE a correct mid-gauge reading is the WRONG way to achieve precision! You wind up getting the correct reading for 'normal' operating conditions at the expense of high end dial accuracy. This 'could' be a real OPPS issue someday......Comment
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