stouro

Good morning Vette People,
I'm continuing working on my 62 327 Vette. 2 questions.
1) The Temperature Sender unit. Is there anyway to calibrate this? I noticed every vette catalog has a disclaimer on this product. I bought a new one from the Chevy dealer and it is 70 degrees off. I tested it with a mechanical thermometer in the intake manifold well and it reads 170 degrees after the engine warms up. the stock electric with the new element reads 240+.
At least I know I'm not overheating! 2) - My speedometer is stuck. cable is
fine took it apart and lubricated it. I'm going to remove the speedometer
soon. I'm reasonably mechanically inclined, any suggestions as to what to
look for in the Speedo and how to refurbish it myself?
Thanks...Take Care,
Shawn :chevy

achapman

Shawn,

I just had my 63 SWC tach and speedo rebuilt and the small guages recalibrated by Auto Instruments in Martinsville, VA. The total cost was $400, which included having the clock converted to quartz. I was very impressed with the work that Gentry did. He quoted me a price of $75 to fix my speedo, which was spinning over 160 MPH at 30 MPH. Very knowledgeable guy and willing to share info. You can reach Gentry at 877.450.0110 and the web site is http://www.autoinstruments.com...
Oh, quick turnaround and he paid for the return shipping.

Andy
63 SWC Black/Red
Born May 25, 1963

JohnZ

None of the available senders are "on the money" for calibration, but I've found the Wells TU-5 (from AutoZone, $6.00) to be closer to correct than any of them. You can experiment and add resistance to the circuit so the gauge reads what an I.R. gun on the thermostat housing shows to be normal operating temperature, or just compare the I.R. shot with the gauge reading and understand what the difference is. Don't use any sealant when you install it, as it depends on grounding to the engine through the threads for proper operation.

John McGraw

As John pointed out, you can add resistance to make it read properly at normal temp, but you can do nothing to make it read right over the entire range. That guage was set to the linearity of the original sender, and it would take master gauge technician to change the response curve of the gauge.
:seeya

stouro

Hey Guys,
Thanks for the practical advice, John I was just wondering about adding a resistor, Would the gauge still read at or near 240 if the engine does overheat? I realize that the entire range won't be accurate, But I was hoping to establish a "correct" normal operating temperature and still have a "warning"
if the engine overheats, hopefully before the steam shoots out of the hood.
Thanks...Take Care,
Shawn :chevy

John McGraw

I think that if you use John Z's reccomendation of sender and fine tune with a resistor for normal running you will get plenty of advance notice of impending boil-over. John has played around with solid axle cars probably longer than anyone on the forum, and has found what works and what does'nt.

:seeya

korvettekev

The ammount of resistance you need to add is pretty low. I spliced a 25-ohm resistor in series with my guage to calibrate it at the 180 degree mark. An easy way to find out what value of resistance you need is to get a variable resistor (like a volume control) with a range of 0 to 100 ohms, put it in series with the wire to your temp meter, and simply dial it in until your guage matches the mechanical guage at operating temperature. Then you can remove the variable resistor and measure its value with a DIGITAL ohm meter, and buy a resistor with the same value. Most common resistors have a 5% or 10% tolerance range, so measure it to make sure it matches your previous reading.

62fuelie

I have installed several of the Wells senders in my cars and otheres. Never found it necessary to trim the resistor.

JohnZ

I use a 0-100 ohm variable resistor (potentiometer) to trim the temp gauge circuit - then read the value and get the correct resistors to duplicate it. Radio Shack has them for about $5.00 (they'll probably have to order it for you from the catalog, or you can find it on-line). Also makes a great tool for checking operation/linearity of fuel gauges, as it's just the right range to duplicate the 0-90 ohm resistance to ground of the fuel tank sending unit.