Thermo Switch not letting fan engage?

[FabriziaSpider]

Hello all,

I recently got this issue with my radiator thermo switch. So last night I went for to a car meet with some friends, we parked our cars and when I got out of my Fiat, there were absolutely no issues, the fan was engaged and kept my car nice and cool. On the way back home me and my buddy were cruising doing 80 Km/h and then I started to watch my temperature gauge rise up and keep rising, so I gave it a bit more gas and then i kept it cool. When I stopped off at the coffee shop my gauge was still high and there was no fan. I was quite angry after just changing my stupid thermo switch, and having my engine rebuilt. So this morning I woke up and got to working. I unplugged the two wires connected to my thermo switch and indeed the fan came on no problem. So I am trying to understand is it possible that my thermo switch is broken after only 400 kilometres? I need to have this issue rectified I do not need to have my cam re machined and pressure tested and more money thrown into it.

I need to fix this issue

I NEED HELP!


Thanks guys!

[4uall]

could be air in the system or other issues

this may help

http://wwwe.fiatspider.com/f08/viewtopi ... verheating

http://wwwe.fiatspider.com/f08/viewtopi ... =6&t=21263

[manoa matt]

If you grounded the switch and the fan came on, then its getting power and the fuse is not blown. The most likely culprit is the ground connection at the drivers side fender ground pod. Check the ground wiring for any hard or brittle spots.

The fan wiring is a simple circuit. Power comes from the blue wire to the fan, and is "hot" all the time. The black ground wire comes from the fan, goes to the thermo switch where it is broken, then up to the ground pod on the fender.

[danaspider]

I agree with Manoa, in that the circuit is not that complicated. The thermo couple in the radiator is just a switch that takes the one side of the motor to ground completing the circuit and running the fan until the rad temp drops. So in the process of looking at a solution, it is important to assure that there is no air in the coolant loop, otherwise the bottom of the radiator never sees water that is hot enough to trigger the fan.

So if you have checked for air in the systems then there is the old "emergency" solution that we used to do to help prevent the over heating. That is to add a relay to a switch in the cockpit that allows you to turn the fan on manually. I used a lighted switch so that I know that it is on. By wiring this correctly you still have the thermo in the loop so the fan can run when the car is hot and turned off. Why a relay, too much current may be pulled by the fan through a switch, a relay can handle the higher load. Secondly if you wire the remote switch for the relay using a 12 V switched source, then the relay drops out when the car is turned off and you will not run your battery down. The common side of the relay should go to ground (the grounding ring in the engine compartment is good), the normally open side of the relay should be a wire that you have spliced off of the cable going to the thermo switch. You want to splice into the wire that is feeding into the switch, not the side going to ground.

In this way the Thermo works as designed, but you have the assurance of manual control. This is sometimes nice in very warm weather and traffic.

Hope that helps.

[manoa matt]

However the 1976 year came from the factory with a relay in the cooling fan circuit. 1975 Was very similar in the wiring so it may also have a relay in the circuit.

[So Cal Mark]

the easy way to test the circuit is to jumper the two wires to the thermo sensor. If the fan comes on then the entire circuit is good and you either have a defective switch or it's not getting hot enough

[FabriziaSpider]

Hello everyone, thanks for all the replies! I checked everything out and let her run till the temp reached 195 and then she engaged, I think the culprit was most likely an air bubble in the radiator causing the issue, that's what my shop manual said. So I got rid of the air inside my radiator and it engaged no problem!

Thanks again!

[manoa matt]

Typically an air bubble will be in the cylinder head as that is higher than the radiator. Alternatively an air bubble can be in the lower radiator hose just below the thermostat.

I still think you have an intermittent ground problem.