Temp gauge testing

[BennSport]

So I’ve been trying to follow the Clark’s garage testing procedure for my dash gauge temp sensor, but I came across an anomaly. The instructions refer to 2 seperate wires on the connector but my sensor only has 1 wire connected to it. Referring to the diagram I’m assuming to proceed as normal, and that my early car doesn’t have a temp sensor alarm. I just wanted to check with everyone else and see what they think.
https://www.clarks-garage.com/shop-manual/elect-19.htm

[c5_pilot]

Correct, early cars only have one pin for the gauge temp sensor. The DME temp sensor does have 2 pins.

[Tom]

So I’ve been trying to follow the Clark’s garage testing procedure for my dash gauge temp sensor, but I came across an anomaly. The instructions refer to 2 seperate wires on the connector but my sensor only has 1 wire connected to it. Referring to the diagram I’m assuming to proceed as normal, and that my early car doesn’t have a temp sensor alarm. I just wanted to check with everyone else and see what they think.
https://www.clarks-garage.com/shop-manual/elect-19.htm

Yes, I believe the early 944 has a one-wire sensor rather than 2 spade connectors like the later cars. Assume yours looks like the one on the right in this pic borrowed from 944online:

sensors.jpg (63.04 KiB) Viewed 1074 times

Just measure resistance to ground and compare to the reference points based on temps. Since ChatGPT is so good at doing tables, I did one for you so you don't have to interpolate so much...

30°F ≈ 2118 Ω
40°F ≈ 1558 Ω
50°F ≈ 1163 Ω
60°F ≈ 879 Ω
70°F ≈ 673 Ω
80°F ≈ 521 Ω
90°F ≈ 407 Ω
100°F ≈ 322 Ω
105°F ≈ 287 Ω
110°F ≈ 257 Ω
120°F ≈ 206 Ω
130°F ≈ 167 Ω
140°F ≈ 137 Ω
150°F ≈ 113 Ω
160°F ≈ 93 Ω
170°F ≈ 78 Ω
180°F ≈ 65 Ω
190°F ≈ 55 Ω
200°F ≈ 47 Ω
210°F ≈ 40 Ω
220°F ≈ 34 Ω
221°F ≈ 33.6 Ω
230°F ≈ 29 Ω
240°F ≈ 25 Ω
248°F ≈ 22.7 Ω
250°F ≈ 22 Ω

[BennSport]

Well I tested the gauge today and it seems to be in order. I’m wondering if my timing belt might be a little stretched causing the water pump to not spin as fast as it should.

[Tom]

Well I tested the gauge today and it seems to be in order. I’m wondering if my timing belt might be a little stretched causing the water pump to not spin as fast as it should.

What is going on with your car? Overheating?

[BennSport]

Ah yes, I should’ve specified earlier. Ever since I purchased the car I’ve always had an overheating issue. I’ve replaced the fan temp sensor, heater core, water pump, thermostat, and flushed the system more times than I can count on two hands.

[Tom]

Ah yes, I should’ve specified earlier. Ever since I purchased the car I’ve always had an overheating issue. I’ve replaced the fan temp sensor, heater core, water pump, thermostat, and flushed the system more times than I can count on two hands.

What's the pattern? Does it just go up and up until it's in the red? Cooler while cruising on highway? Just stays uncomfortably high all the time? Worse when you drive hard? My car just ran hotter than I wanted all the time and I tried all the tricks too, with minimal success. I finally bought a factory new radiator and that completely solved the issue. The original owner of my car had a coolant leak and would top it off with the garden hose which ended up clogging the inside of the radiator with calcium and mineral deposits.

P.S., whatever the cause, there's a near-zero chance it's due to a loose timing belt....

[BennSport]

Historically it would always sit between the second and slightly past the third line, and when the fans kicked on it never fully dropped to the second line. Recently however, the car has been hovering closer to the third line which leaves me worried, especially considering temps where I’m at are in the 30s. Also might be of relevance but I think I’m due to retighten the belt to its used state, as I haven’t done that since I installed the new belt last year .

[Tom]

Historically it would always sit between the second and slightly past the third line, and when the fans kicked on it never fully dropped to the second line. Recently however, the car has been hovering closer to the third line which leaves me worried, especially considering temps where I’m at are in the 30s. Also might be of relevance but I think I’m due to retighten the belt to its used state, as I haven’t done that since I installed the new belt last year .

So even driving down the highway in 30F weather, it stays close to the third (97C) line? If the gauge is accurate, I'd agree that suggest something isn't working as designed...

[BennSport]

Correct. I’ve been looking into new radiators, but I’m having trouble finding a three row one. I figure since I’m going to be replacing, I’d want one that performs better than stock