C1 temp gauge-Jack Humphrey

[Howard M.]

I'm working with '60 283 base engine with a temp gauge problem. I did a boiling water check of the new sender with the following results: 550 ohms @ 83*, 313 ohms @ 120*, 170 ohms @ 160*, 90 ohms @ 212*.
All the other data points fell right on the curve. I did a 50 ohm check of the gauge and it pegged at >240*.
When I operate the car, the gauge pegs at 240* although the thermostat hsg is 185* (180* thermostat) and the top of the radiator is 197* (all readings with an IR meter). I presume that this indicates that the engine temp is acceptable. Your posts indicate that you do not approve of adding resistance in the system but short of removing the sender and gauge for calibration, how do you get around this resistance difference problem?
It means that if the sender or gauge were ever replaced, the system requires recalibration. If I were to try a new sender, how would I know it to be any different in resistance vs temp than the one I have?
I took apart an old sender but I don't know how it functions with the spring and slug.
Thanks for any advice. Hal

[John M.]

Re: C1 temp gauge-Jack Humphrey

Howard,
I just took a hand full of sending units and tested them all until I found one that matches the original Delco calibration curve. I was having my car judged, so all the senders that I tested were old, original units. Out of 6 senders, I found 2 that were very close to the factory curve and they made the gauge read right on. It was kind of a pain testing the sensors, but the end result was worth it. I heated the sensors in the oven and plotted the resistance curve at 4 different points. Obviously, adding resistance only makes the gauge accurate at one place on the range, and at all other places, it will be off dramatically.

Regards, John McGraw

[Dwight Bedsole]

Re: C1 temp gauge-Jack Humphrey

Jack,
Did you check to see if your temp gauge originally had a resistor connected between the silver and copper post. This was typically a 90 ohm ceramic resistor. If the resistor has been replaced with too high of a resistance the gauge will read hotter than the actual engine temperature.

Dwight

[Les Jacobs]

Re: C1 temp gauge-Jack Humphrey

My C2 gauge read approx 220 when the coolant 180 or so. Since I was not concerned about the accuracy of the low end temp I added a resistor to make the gauge accurate @ 210. (my thinking was once I get close to that temp I need to worry anyway). Afterward I compared the gauge and actual temp and found it to be very accurate between 180 and 210. The car has never been hotter than 210 since (2yrs) so I don't know how inaccurate it becomes. Les