Technical Temp Sensors

[mihailou]

Quick question. Water temp sensors
Red sensor to firewall end of engine ??
PO has red to front and black to firewall .My research shows this is in reverse. Before installing new sensors can anyone confirm ie Red to firewall Black to front.
Thanks
Dave Hewitt

 

[124BC1]

You haven't stated which engine you're referring to, but assuming that it's the same engine you asked about recently, i.e. 124 TwinCam, here goes:-

Looking at :- https://www.midwest-bayless.com/c-24-cooling_Fiat-124SC-0.aspx


would appear to confirm Red-topped sensor to firewall and Black topped-sensor to front.
In the good ol' days, there weren't any red-topped sensors, both were black-topped, but I do recall the one nearest to the front of the engine was for the coolant temperature warning light.
If you're not sure which type of sensor you're dealing with, you can use an ohm-meter between the sensor terminal and earth (ground) - the resistance of a sensor for a temp gauge will (iirc) decrease as the coolant heats up, ), whereas the resistance of a sensor for a warning light will not change until the coolant gets really hot (c.100*C) then will drop to almost zero ohms.
At the cylinder head, the green wire goes to the gauge sensor, the green with black tracer wire goes to the warning light sensor (although I've seen both wires being green, no tracer) but iirc the lengths of these 2 wires is different and this will indicate to which sensor they should be connected.

 

[mihailou]

You haven't stated which engine you're referring to, but assuming that it's the same engine you asked about recently, i.e. 124 TwinCam, here goes:-

Looking at :- https://www.midwest-bayless.com/c-24-cooling_Fiat-124SC-0.aspx


would appear to confirm Red-topped sensor to firewall and Black topped-sensor to front.
In the good ol' days, there weren't any red-topped sensors, both were black-topped, but I do recall the one nearest to the front of the engine was for the coolant temperature warning light.
If you're not sure which type of sensor you're dealing with, you can use an ohm-meter between the sensor terminal and earth (ground) - the resistance of a sensor for a temp gauge will (iirc) decrease as the coolant heats up, ), whereas the resistance of a sensor for a warning light will not change until the coolant gets really hot (c.100*C) then will drop to almost zero ohms.
At the cylinder head, the green wire goes to the gauge sensor, the green with black tracer wire goes to the warning light sensor (although I've seen both wires being green, no tracer) but iirc the lengths of these 2 wires is different and this will indicate to which sensor they should be connected.

Thanks so much for your reply it has put my mind at rest re replacement. Have yet to check their operation but am hopeful this solves my problem. As you said both wires are green but not a problem due to the wire length.

Once again thanks

 

[mihailou]

Thanks so much for your reply it has put my mind at rest re replacement. Have yet to check their operation but am hopeful this solves my problem. As you said both wires are green but not a problem due to the wire length.

Once again thanks

Well this has turned into an adventure. Every advice I have received and info from sensor sellers has proved wrong. The black sensor which should be to the front does not fit. Apparently having a bigger nut ( ? ) means it fouls a casting on the head even though both sensors have the same thread size. Have reversed the positioning and even though I have not tested the temp light ( haven't got to high enough Temp ) the gauge is now working perfectly. Many thanks to all who helped but it appears installation of the sensors is the only way to prove fitment