Some Q&A About the Spitfire Temperature Gauge

The Temperature gauge on my '79 Spitfire suddenly quit working. (Kind of like me at 5 o'clock!) The needle doesn't budge. The gas gauge works OK. I am getting the pulsed voltage at the sender unit lead (measured with my digital multimeter), about one pulse every second. Resistance at the sender is varying with temp, from 33K ohms hot to 147K cold.

1. Are these sender readings OK? Could anybody check theirs as a comparison?
2. If I short the sender lead to ground, will I hurt anything? [I don't want to ruin my voltage stabilizer or gauge.]

more from Atwell.......

I just installed the new sending unit for the temperature gauge, and it works fine now. So in case anyone else has this problem, the resistance of a working sender is:

COLD: 1000 ohms HOT: 50 ohms

Measurements were taken with the sender wire disconnected, terminal to block, with a digital VOM.

Atwell Haines

Atwell, last weekend I went through a test which you might find interesting. Put a new sender in a pot of water on the stove to measure temp vs resistance. I think many of our cars use the same senders (at least TR5-8, Spits and GT6s). Here is what I found.

res (ohms)      deg C   deg F
500             42.0    107.6
450             46.0    114.8
350             49.0    120.2
250             55.0    131.0
200             61.0    141.8
150             70.0    158.0
100             92.0    197.6

Then my VOM started going funny. I thought it might be from the leads getting hot from being in contact with the hot sending unit. So I measured (with different leads) as the water was cooling:

res (ohms)      deg C   deg F
70              78.0    172.4
100             68.0    154.4
125             60.0    140.0
150             52.0    125.6
180             50.0    122.0
380             48.0    118.4

I live at about 2000' above sea level so the boiling point is lower than 212 F (100 C). Never did get to the 50 ohm value you saw. (This was a brand new Intermotor sending unit from TRF - I have not tested my old one yet but it seems to show on the low side, never gets above 1/4 unless idling in hot summer weather, then maybe almost 1/2).

(If you recall my earlier post on this, the gauge reads 1/4 at 200 ohm, 1/2 at 100 ohm and 4/4 at 50 ohm. Unfortunately when I did this test, I connected the gauge to the battery directly without going through the voltage regulator. As I can't get to my car 'til the weekend to redo this part of the test properly, I don't have the actual voltage regulated values for the gauge.)

Peter Zaborski

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