Overheated Tempreature Sending Unit Operating Range.

[Jim Fierst]

I checked the archives befor posting this and have posted it on other Forums. Does anyone know the range of the overheated cooling system temperature sending unit . It is used in all Fiats and Lancias running the same type of temp. gauge. I would presume that it makes the circuit at some specified temp or range of temperatures. I am running the A/C here in AZ in the summer and while the radiator is fresh etc the system runs in the upper range of the zone.. The P. P.O (previous to the previous owner) did not bother to replace the sending unit for some reason and I would like to have it working and know what is is telling me.

[Will]

Jim;
There are two sensors in the head- the temp sender and the warning light switch (which also pegs the indicator).

They have black or reddish connectors, I don't remember whicxh is which but throw an ohmmeter on them and the one that reads infinite is the switch.

I assume it's the value for the switch that you are looking for. I don't know this offhand (and it probably varies between units a bit) but I can tell you how to test yours:

Dangle it in some vegetable oil in a pan and check continuity. Heat the oil slowly and monitor the temperature until the thing switches on. My guess is this is going to be around 230 degrees or so. Then let it cool slowly, and keep an eye on the temp until it shuts off.

Measuring on the heating and the cooling cycles is important because it gives you the hysterisis of the unit and an idea of the thermal response due to "soak" time.

Note: You can't test it in water because you can only get water to about 205~208 degrees on your stovetop. Use veggie oil so the wife doesn't smack you in the head with the pan when she sees it full of Pennzoil.

Please report back as I'm curious too- I just did a Davies Craig pump controller thermistor the same way and I'd post the resulting graph except I don't know how as it's on my local machine and I would have to upload it.

[Jim Fierst]

Thanks Will,
At another Forum , some one posted the operating range was 233 to 244 degrees which makes sense.
The sending unit in my 79 LBZ is in a waterpipe and not the head. When I removed it I found that it is very different than the ones used in the Fiats.It is much smaller. From the looks of what is left of it I am guessing that it was a switch like a fan switch with 1 wire to ground and the other to the gauge. It would need to work that way as the water pipe might not provide a sufficient ground.
Good luck on finding one.

[Will]

Jim;
I'm assuming since your LBZ is a '79, it's not FI? If it were, the devices in that rail (if it is a long steel pipe that goes over the top of the motor between the cam towers)would be the Thermo time switch (brown connector) and Coolant temp sensor (white connector) and they would be the Bosch 2-conductor clip-type unipolar connectors.

If you are cobbling an engine together, and these devices happen to be there, ignore them and look at the head itself for the indicator sender and the overheat sensor. Somebody may have added a FI rail and left the sensors in place just to act as plugs.

The indicator sendor and overheat switch should be IN THE HEAD, not in the water outlet.

UNLESS the device you are talking about is actually tapped into the cast aluminum head outlet "T" right at the bell of the water outlet. This is common to one of the FIATS. I'm not sure which since I only saw two of these outlets and neitrher was on a car. Bruce Matthews told me he thought it was for a 125, but I'm not sure. I'll bet Chris Obert would know where to get one of these, if that's what you are looking for. Again, I only saw the water outlet so I can't tell you what the atached sender is supposed to look like, and I think I remember the threaded bung was smaller than the standard one in the head, but that was a few years back and my memory is far from perfect.

I just checked boiling points for glycol because I was curious, they are as follows:
50/50: 265F
70/30: 276F

Just an FYI so you know the margin that switch could operate in. It should not be too hard to find one from another application if you get stuck, and make it work with a little retapping or a bushing.

Hope this helps.

[Jim Fierst]

My LBZ is a carbed 1979 and the overheat sensor is in the pipe that wraps around the rear of the engine. It is stock and and the connector wire matched the color on the wiring diagram. I could not locate a second sending unit in the head . There is still some emmission stuff there and perhaps it is burried under that. Some time this coming winter I am going to pull the head and replace it with a fresh Fiat head , a mild intake cam and a bigger carb. At that time I can use the Fiat in head sensor.Till then it will stay as it is.

[Will]

Sounds like you answered your own question- if it's stock, one of the usual suspects probably has a few on the shelf. I'm pretty familiar with the FI Zags but not the carbys- and I've never seen an 8V TC FIAT/Lancia head that did not have the senders in it. In your case, you might find the gauge is different too (the ones I'm used to need both head sender ands overheat sensor connecxted to work properly)