'64 mk1 matching temp guage to sensor

[robmorgan]

Hi guys
I have an early'64 850. Am struggling with the temp guage, the early type with adjustment screws, which doesn't work. It receives power when the ignition goes on(the needle twitches) and if grounded goes to H. I've tried it with gtr104, gtr101, voltage stabiliser, no voltage stabiliser (it didn't have one originally).

I tested the sensors by wiring them up on a test bench to a battery with the guage then dunking them in boiling water, which got a small amount of movement out of the needle but no more than 5mm.I got it to move to H by holding the sensor in a flame so it seems to work and be progressive but doesn't give anything near a normal reading.

The original sensor was a gtr102, I have two but they seem as ineffective as the test so I don't know if they work. Any advice? I heard that the matching of sensor to guage is important but the original sensors are unavailable and I don't know of an equivalent. Could the guage be at fault? If so, is it possible to calibrate it?
Cheers
Rob

[NickD]

The GTR102 sender used with the early temperature gauges has a lower resistance at all temperatures than either of the later GTR101 & 104 versions, so using these later senders with the early gauge will never show much of a reading.

Senders can be checked by testing their resistance when heated in water to various temperatures. A GTR102 should have a resistance of about 300Ω @12˚C, 230Ω @35˚C and 26Ω @82˚C. The GT104 reads about 580Ω @12˚C and the GTR101 725Ω @12˚C so easy to work out which is which.

A GTR102 should have a green plastic section around the terminal and a genuine Smiths one will be stamped TT-3800/00A

Intermotor also produced an equivalent sender as part no 5270, and these still sometimes turn up on ebay

[robmorgan]

I thought as much. Thank you, this helps a lot.
Cheers
Rob