Where are the water temp sending units?

[PleasantSpider]

We are having an issue with the thermostat and suspect a problem with water temp sending units. Can anyone verify where these might be? We think there are 2 that are sitting in between the spark plugs....or are these something else? AND is there a diagram of this somewhere? The diagram I have doesn't actually show their exact location but show them in the vicinity.

[So Cal Mark]

they are in the top of the head, inbetween the spark plugs

[PleasantSpider]

There are two there, correct? That's what we see. Just trying to be sure they are what we think they are...

[courtenay]

Yes, there are two. On my '80 Fi, the one closest to the radiator 'pegs' the needle. The one closest to the firewall controls the needle. I, and a number of others here, have disconnected the one that pegs the needle.

[Piccola]

the one "near" the radiator is a thermal switch ( white black wire ). It controls the engine temperature and when is hot it close to ground otherwise is an OPEN circuit.
the one "near" the firewall is a thermal resistor ( white green wire ). it is connected directly to the temperature gauge which has a + 12 and the negative comes from the resistor ( connected to ground ).
if you want check the thermal resistor just take your multimeter in DC and check the Voltage between + and Thermal resistor output. voltage will drop up while you warm the engine.
If you want check the thermal switch , same as above but you will see 0V when engine is cold or 12V when engine is overheated ( switch is activated ).

[fiatfactory]

.

[courtenay]

I disconnected the switch because it failed and was continually pegging the needle - even though the engine was operating at normal temperature. I do check the fluid levels regularly and simply haven't gotten around to replacing the sending unit yet.

[fiatfactory]

.

[btoran]

can someone pls post a picture of where these two units are located and which might need to be replaced on my car?

my temp reads VERY low. all the time. it barely moves from dead cold at all, although the engine is obviously hot. i will shoot the head with a laser temp gun to confirm actual temperature but it can't be as low as indicated on the gauge.

[courtenay]

Not sure a picture is necessary. Both sensors are pretty obvious - located between the plugs on the top of the block. I'm not looking at my engine right now, but if I recall correctly, that apart from the plugs, they are the only other things screwed into the top of the block.

[aj81spider]

Here's my engine - out of the car - shot from the back (#4 is the plug closest in the picture).

The two thermostats are the hexagonal things on each side of the #2 plug. The socket is in the hole for the #3 plug.

Hope this helps.

[btoran]

AJ - that's worth 1,000 words. thanks.

so, what is the proper operating temperature?

[aj81spider]

Mine runs with the needle right on 190.

[btoran]

maybe because my car came bypassed, but the radiator fan is always on. temp is shown on the gauge as 140. i verified that with a heat gun. is this too low and if so, how do i unbypass the radiator switch?