WHERE DOES IT GO TO

[Baz]

Before I tear it all out maybe someone can tell me where the two temp wires that connect to the sender units in the top of the head go to under the dash. The wires have gone hard and split and I need to replace them.

Tar
Baz

[manoa matt]

They go to the water temperature gauge in the dash. One is the temp sender that tells the gauge what the water temperature is. The other one pegs the needle in the gauge when it gets over a certain temp threshold as a means to warn you prior to the car overheating.

[divace73]

there should be a resistor inline somewhere for the black temp sensor (the one that send the needle to max)
(according to my wiring diagram)

[manoa matt]

For a carburated or FI car the wiring and sensors are the same and are as follows:

The sender with the green wire with white strip is the water temperature sending unit(sensor closer to the front of the head), while the sender with the grey wire with black stripe is the water temperature thermo switch (sensor near the back of the head, pegs the needle) The water temperature gauge resistor is in line with both of them. It is located in what appears to be an individual fuse holder up under the dash above the gas pedal. Both sensors are tied to each end of the gauge resistor with only the green wire with white stripe making its way to the dash gauge.

Referring to the senders as black or brown is inaccurate as different manufacturers used different colored plastics, some are even red in color. The stock Fiat senders were all a dark brown color. Also the sensors look almost identical when screwed into the head, however the temp gauge sender is longer than the temp overheat switch.

http://stores.auto-ricambi.net/-strse-C ... gories.bok

[courtenay]

Now I'm really confused - Matt - could you check my temp sensor thread in the Enging and tuning section and give me some advice please? I've disconnected the sensor at the front of the block (nearest the fan) and the both the engine and gauge seem to be operating as they should, given the temp readings I've taken with my IR temp probe. When I reconnect the front sensor, the needle shoots up towards the red zone. Am I in danger somehow running with that sensor disconnected?

[manoa matt]

Courtenay, It sounds like the rear sensor (overheat warning is stuck open/closed. Replace it and see what happens. It also could be a ground issue since the sensor grounds through the body to the head. If its wrapped in teflon tape it might not ground. An additional grounding wire from one of the studs on the cam shaft retaining plate to the firewall is a good idea.

The temp sending unit in the head works on resistance. The higher the electrical resistance the higher the gauge reads. With an aging electrical system and several connectors along the way you can accumulate resistance at each connection. If your temp gauge constantly reads high but you have confirmed the actual temps with a laser thermometer then to get the gauge to read "more accurately" simply go through all the connection points and clean them up and add a little dielectric grease to prevent oxidation of the contacts. You also need to clean the contact points inside the temp gauge resistor housing and the ends of the resistor too. I believe the resistor is housed in a red plastic holder (it could be blue too) It will look like a big fuse that is wrapped with a tiny copper wire. Be careful, if you break the tiny wire of the gauge resistor if may be tough to find another as there is probably no published specification for the original.

[divace73]

If your car is fuel injected, there is also a temp sensor in the T piece (this is only for the Fuel Injection), it has nothing to do with the temp gauge.
The fuel injection system is completely independent from the rest of the car (a great advantage for upgrades)

In the head itself the sensor the closest to the front is for the gauge movement and the sensor in the rear of the head is for the max position (just like a switch)

[courtenay]

Thanks, Matt and David. It appears my sensors are in the reverse position from what you're describing. The sensor with the green/white wire is closest to the firewall rather than the front of the block. The other one (grey/black) is nearer the fan side of the block and this is the one I have disconnected. The needle is now registering what appears to be the right temperature. While I am going to replace the apparently faulty sensor and clean the contacts (already checked and cleaned the engine ground) is there any risk with running without the "needle peg" sensor disconnected?
Bruce

[So Cal Mark]

no, you can leave that sensor disconnected without any adverse effect on the gauge operation

[courtenay]

Thanks, Mark. That's the answer I was hoping for!
Bruce