mk1-forum.net

I was reading viewtopic.php?f=3&t=19902&p=165297 and doing something experiments for the continuing battle to understand temperature behavior on my car.

Basically I wanted to know what a 'Black' sensor would read, compared to a new 'Red' which is supposedly correct for '67 Mk1 Cooper S.

Materials:

New old stock 1966 Smiths voltage regulator
Known good Smiths temperature gauge
12v jump start battery
Croc clips and leads
Digital ohm meter
GTR101 : Old stock Black Smiths TT-3803/00A
GTR104 : New stock 'Red' (actually white) generic from 7ent

I measured in a saucepan of water the temperatures of each sender at 5 points on the gauge scale, basically at C, N, H and roughly half way in between each of C/N and N/H

Resistance measured according to gauge deflection:
C = > 200 Ohm
C/N = 115 Ohm
N = 79 Ohm
N/H = 68 Ohm
H = < 56 Ohm

The results measuring temperature against the gauge are:

Black:
C = 62°C
C/N = 75°C
N = 88°C
N/H > 90°C
H = untestable with water

Red:
C = not tested
C/N = 62°C
N = 75°C
N/H = 88°C
H > 90°C

These results are all very approximate. Basically plus/minus a couple of °C as I couldn't maintain exact temperatures while taking both powered and unpowered resistance measurements.

But they do show a trend that the Red is normalized one-quarter (25%) of gauge reading higher than Black for the same temperature.

Thanks for posting this up here.

I too did some similar checks a little while back as all the Senders I've tried for a long while now all seem to make the new Smith's Gauges over-read. I don't have a reliable old gauge to compare against.

If I remember, I'll dig out the results of what I measured, and post that up here too.

Just touching on Gauges here, I'm un-sure if you are aware, but to some degree there is adjustment in the gauge itself at the C and H ends.