Adjust the Temperature gauge

[CLIFF_MK1]

As part of restoration 3 years ago, I had Temp gauge rebuilt along with my other gauges. Always ran hot (225+) even though engine was normal temp (185 degrees). Checked everything, replaced regulator twice, yes 10 volt to gauge. Replaced Temp sender (SS), and even replaced gauge. No difference.

Read all the articles, including using resistors to adjust temperature, and Ohms for different degrees for Tiger sender. No other sender really available that met Ohms needed to match gauge.

I found this neat temperature gauge adjustable calibration resistor. It's made for early Corvette's (C1-C3), which I assume have similar problems with the temperature gauge. Sold by Corvette Central. You install it in series with the wire going from the sender to the gauge. Then, it has a screw that has 17 turns with a range of 0 to 50 Ohms. Now this only works if your gauge reads high, not low. Run your Tiger to operating temperature and check with infrared thermometer and turn the screw until your gauge is reading that temperature. Secure your wiring. The most difficult part of this is twisting your body to get under the dash to do the wiring.

So, it just feels great to cruise down the lane and look at the gauge and see an accurate reading instead of being pissed off that it doesn't work. So far, so good; I'll let you know if it stops working. Cliff

 

[HolyCat]

Great Find

Cliff,

This sure beats using fixed value resistors, determined only by trial and error. As you said, this variable resistor only helps if one's temperature gauge reads high, not low. I assume you calibrated the variable resistor to get your temperature gauge to be accurate at normal operating temperature. The gauge may not be as accurate for temperatures higher or lower. What a great solution! Thanks for sharing.

 

[1966 TGR]

This is a great find, Cliff. I had to trim my temp gauge with a fixed resistor years ago. But in my case the gauge read too low. I think I got a new Autometer sender which worked great, and then had to fine tune with the sender in a pot of boiling water. Been working great ever since.

 

[Warren]

Great job

Cliff. That would have saved me at least two or more head stands and many precious follicles of hair on the reverse lock out on other cars. As a sidebar here's my temporary marker as to how hot this car can get in a 75 degree garage idling garage at 180. I suspect this is the original thermistor installed. Wasn't there a Tigers United testing on what values to look for?
PS I'm under 190 at the green tape. 6 blade LAT fan reduced diameter pulley car is cold blooded believe it or not.

 

[CLIFF_MK1]

Here's some info on stock Tiger Temp sender from Stu's research. Here's a graft of these figures in F. One question which has been discussed is the effect of installation of a resistor on accuracy of measures above and below the temperature which has been set with the resistor. Like the question that Dave mentioned about possible lack of accuracy above and below where I set my resistor at normal operating temperature, in my case 185 degrees.

It would be helpful to have an engineer or someone who can say what the effect of installing a resistor at a fixed point on the gauge. I just installed my resistor and adjusted it at 185 degrees. When I drove around as the day got warmer and got into stop and idling, the gauge did begin to climb some what as would be expected. I didn't think to get out and use my infrared tool to see if the gauge matched what the actual temperature was (in other words is the gauge still accurate?).

Even with the resistor installed, the engine temp sender is still working. According to the graph, the slope is uniform from about operating temperature to over boiling point. So does this mean that the gauge with the resister installed an set at operating temperature still accurate at higher temps but not at lower temps? (because of the severe slope at lower temps?

 

[Too Tech]

The supplied temp Vs Ohm data was mis-plotted on the graph. The graphed line fails to show the slope change between 212 F and 248 F. So essentially the graph should have 3 distinct slopes (140 to 176 F @ 73 ohm, 176 to 212 F @ 36 ohms, and 212 to 248 F @ 17 ohms). So using a resistor to tune the gauge to the actual sender temperature would only result in an fairly accurate reading within 1 of the slopes, but not the other 2.
But all is not lost. Ask yourself at what temperature are you most interested and tune the gauge at this point.

Personally I tuned my gauge to be accurate at 220 F. So if my gauge reaches 220 F, I know the coolant is at 220 F and my cooling concerns are real.