Temp Sensor in the thermostat housing.

[RogerH]

Hi Folks,

 a long while ago I replaced my cooling system temp sensor with a   GTR104 (InterMotor) from Moss.  This had the red collar and looked like what had come out.

Some time later (ages) I noticed that the temp gauge would drop to zero  and then come back on line. 

This sort of coincided with going fast (zero) and slow in traffic (high reading).

Today I tried to measure the resistance of the sensor and could not get any sensible reading with it cold.

So I found some used/NOS sensors .   The old  used one measured apprx 1500 ohms at room temp.  I had another sensor  that looked new and had a resistance of 500 ohms at room temp.

The newer looking sensor (500 ohms)  gave a steady reading at max. The needle hard on the 'H'

I then fitted the old used one (1500 ohms)  in the driveway this gave a steady reading at just over 50%.

 

So is it normal to buy a sensor with no clue of what will happen !!

Is there a supply of standard sensors that work properly

 

Roger

[RobH]

It's difficult to find much information on those sensors but I do have some (dubious?) figures for  the GTR104: 

30 degrees C.  520 Ohms

40....350,    50...270,    60....180,   70...145,  80....98,   90...65,   99....47

A GTR108 (TR6) is apparently 1400 Ohms at ambient - I wonder if that is what you have? 

 

[RogerH]

Hi  Rob

thanks for that. At least my numbers actually exist.

Not sure where a TR6 sensor came from but after my test drive (just now) the needle is sitting down the centre of the dial.

Roger

[BlueTR3A-5EKT]

I have a what I believe to be a NOS Smiths sender unit for a TR4.

it reads as follows at 28°c ambient in the garage.

Edited August 9, 2025 by BlueTR3A-5EKT

[Z320]

Hi Roger,

for another Forum I posted thus some years ago:

sensor spamped

Smiths
Motor Accessories
England

on the hex part stamped "2-7" and "TT 3802/00".
(should it be a "TT 3804/00" on late TR4 und 4 A?)
I measured 880 Ohm at 20°C and 90 Ohm at 100°C.

My gauge is not the electric heated but voltage comparing (bridge)

Ciao, Marco

Edited August 12, 2025 by Z320

[stuart]

We have been through this a few times over the years, the one with the red ring is TR7 and Dolomite. The correct one is the one with the black ring.

Stuart.

[RogerH]

Thanks Stuart,

oddly Moss and co do not show a black collar on the sensor.

I'll pop into a car parts factor tomorrow and see what is out there.  - loads on ebay (next port of call)

 

Roger

 

[stuart]

27 minutes ago, RogerH said:

Thanks Stuart,

oddly Moss and co do not show a black collar on the sensor.

I'll pop into a car parts factor tomorrow and see what is out there.  - loads on ebay (next port of call)

 

Roger

 

That should be the GTR108 

Stuart.

[roy53]

There has been a problem with these for sometime 

As I mentioned before when I contacted the TRshop they would not sell them as so many problems 

solved mine with forum help by adjusting the gauge 

Roy

[Lebro]

Yes, it's doable, this year I converted my '3 to electric temp & fuel gauges. I bought a "red" sender from Moss, & calibrated the gauge to match it.

Bob

[RogerH]

Hi Bob

any clues on what you did

 

Roger

[RobH]

Calibrating Smiths electric TR4 Temp gauge - by Peter Sherman .........

 

The two slotted adjusters don't turn like screws - they sort of slide sideways. 

Edited August 11, 2025 by RobH

[RogerH]

Thanks Rob

That's tomorrow sorted

 

Roger

[Lebro]

The adustment is not easy to do smoothly, the levers inside tend to be quite stiff, & want to move in jerks, the slots into which to insert the adjustment tool (usualy a screwdriver) are oval, rather than being slots, so not very friendly to use, however go slow & carefully & you should be ok. The third thing you can adjust is the angle of the needle by gently bending the base of it.

Bob