two coolant temp sensors ?

[geoff]

so now my 2000 spider is running at a nice temperature - with Evans' waterless coolant, I am happy in france !
But.......
from time to time the temperature gauge jumps to "hot - damn hot" (to quote Robin Williams in good morning vietnam);
Seems there are two "devices" between the plugs on the block. One a switch (with one wire out) and the other a sensor (with a pair of wires).
In the real world I would expect the single wire output to go to a warning light and the two wires to go to a gauge to show the temperature - however in FIAT world it seems that they all go to the gauge (how do you spell this word !) and the "one wire" switch sends the needle off into infinity. .................or am I missing something ?

[courtenay]

On my '80, the temp sensor closest to the front of the block, i.e. the radiator, has one wire and "pegs" the gauge. I had the same problem where my gauge would suddenly read "hot- damn hot". I disconnected that sensor and the gauge reads just fine now. I do have a replacement sensor, but haven't been able to get a socket on the old one to replace it. I gather a few others on the Forum have had similar issues and run without this sensor connected.

[Exit98]

I finally resolved the "pegged" needle problem by spicing in about 10" of new wire replacing the cooked old wire and adding a new spade with a cleaned up connection. My sensor wasn't the problem.

[131]

gauge (how do you spell this word !)

"Gauge" is correct, the yanks sometimes spell it without the U, as in "gage". The misspelling "guage" would be pronounce gwage.

[geoff]

don't you think that the swith would be better if it illiminated a warning light rather than "pegging" the gauage?

I bet you race/rally cars had that much clearer warning system. I think i may do it on mine

[geoff]

seems I was a little mistaken. Both of these sensors have only one wire each.
The first sensor between plugs 1 and 2 has a grey/black wire and the second sensor between plugs 2 and 3 a green/white wire.
I m assuming that the one between 1 and two is just a switch which "pegs" the gauage to max and that the other is a variable resistor which varies the gauge. Can anyone confirm this please?

I think that my problem may be with the gauge itself because this first sensor is not permanently earthed - indicating open circuit - but the gauge is pegged to max.

[4uall]

Here's a little video that might help

https://youtu.be/8DtcIlkt4BY

[gchocevar]

Hi,

I am having the same problem on my 79 Spider. The temperature was always hot, or pegged, but the fan switch operated normally, and it never overheated. The IAP video was correct for the 78 because it has a light. The 79 does not. As the video states, the front wire connects to a high temp switch, the rear to a temperature transducer. I removed the switch wire to get my gauge to read correctly. Following my 79 schematic, I found that the switch is wired in series to a resistor underneath the dashboard. These are both wired in parallel across the gauge terminals. Both the switch and the temperature transducer are both monitoring head temperature. I am guessing the operation on the 79 is that the gauge reads the normal temperature. If their is an overheating problem, the switch pegs the meter.

Now I need to find out if the switch is coming on too early as the engine heats or are there two transducers in parallel. I like the suggestion of mounting an idiot light to the front switch like the 78's and earlier.

[geoff]

yes, one of may shop manuals for the Argenta which uses the same 2.0L OHC engine speaks also of a warning light.
I think I will fit one instead of orr as well as pegging the gauge.
I don't want to spoil the originality of the car so can someone please tell me where the warning light is on the '78 model so perhaps I can copy that on my '79.
thanks
geoff

[geoff]

I would like to revisit this topic here once more.
With regard to the red temperature sensor - the one which varies the needle on the temp gauge - does anyone know its resistance values - when the engine is cold and when it is hot?

[18Fiatsandcounting]

I would like to revisit this topic here once more.
With regard to the red temperature sensor - the one which varies the needle on the temp gauge - does anyone know its resistance values - when the engine is cold and when it is hot?

I just measured it (cold) on my '71 spider, and it's about 3,000 ohms. I can't say what it would be hot, but my guess is that it is in the 10s of ohms (perhaps 30 or so).

-Bryan

[gchocevar]

Hi Geoff,

See my post 103. I remove the switch wire from the gauge, cut the resistor, and turned my seat belt warning light into a high TEMP light.

Temperature runs fine, I have a second warning with the light, and my fan kicks on and off as required.

Good luck,
Greg

[geoff]

Hi Greg, good idea to use the seat belt light but I am not sure if it will pass the technical control here like that!
Measuring my sensor, it is about 100 ohms when cold and 4,000 when hot so that would correlate with yours.
I heard that the original spiders had a high temperature warning light and would like to know where that was located.
regards
geoff

[18Fiatsandcounting]

Geoff, on my early spiders, there was no high temperature light, but there was a high temperature indicator in the form of a second sensor switch on the cylinder head. This switch would send the temperature gauge all the way pegged to the right, into the "red zone" of the gauge. When working right, this "overtemperature indicator" would kick on when the engine temp reached around 230 to 240 oF.

The sensors for these are notorious for failing, and even when they slowly go bad, they act as a parallel electrical circuit to the regular temperature sensor, thus throwing off your temperature gauge reading. A common source of Fiat head scratching.

-Bryan