Cooling Fan Installation

[Sparky]

Better yet, get yourself a power-probe, it's a multimeter and it can be used to supply power and ground to circuits which makes testing and actuating things like relays, fans, and lights far easier. They used to cost hundreds of dollars, now you can get the 3rd gen on Amazon for under $50 (the features on the 4th gen are really targeted at fuel injection diagnostics).
https://www.amazon.com/dp/B00G4YUWMC

[cyberborikua]

Waited for a "warm" day to test the fan relay installation. Today it was about 71 degrees and good enough to test the relay. Fiat took its sweet time to reach 190 degrees but all worked as expected. The relay kicked in the fan by 190-91 degrees and I let it complete a few cycles on and off. Very happy with solving the issue! Used the same relay I had, just ran a new 12v wire to the alternator and that made the trick!

[spider2081]

Nice

[zachmac]

So, why would anyone need a relay at all for the fan? The fans as wired from the factory use a wire that is always hot from the fuse box to the thermo switch that closes on high temp to complete the path to ground. Once temp drops it opens shutting the fan off. If you are concerned about a voltage drop from the factory supply wire just run a wire from the alternator hot to the thermo switch in place of the normal hot supply with an inline fuse. No need for a relay. That way the fan works the way Fiat intended, any time the switch in the radiator sees above the temp setpoint it kicks the fan on, whether the car (ignition) is on or not. The fans from the factory will cycle after you shut the car off if the residual heat in the radiator justifies it.

Lots of places a relay makes sense; the wipers, the lights, electric fuel pump, but not for the fan. Just adds a failure point and complicates the circuit IMO. What am I missing? Is there a concern that the thermo switch itself causes a significant voltage drop?

[spider2081]

So, why would anyone need a relay at all for the fan

There are a number of post in Fiat chat rooms about replacing failed fan switches in the radiator. One possible case for this could be the high start current of the coolant fan motor. The replay isolates the switch from the fan motor current. Another reason for the relay is the fan power is then taken directly from the alternator output post or the starter battery post. This eliminates (bypasses) all the connections between these points that pass through the firewall to fuse panel and back through the firewall.

Agree it's an added part to fail but I am pretty sure the relay circuit can have connections than the factory circuit.

[zachmac]

So, why would anyone need a relay at all for the fan

There are a number of post in Fiat chat rooms about replacing failed fan switches in the radiator. One possible case for this could be the high start current of the coolant fan motor. The replay isolates the switch from the fan motor current. Another reason for the relay is the fan power is then taken directly from the alternator output post or the starter battery post. This eliminates (bypasses) all the connections between these points that pass through the firewall to fuse panel and back through the firewall.

Agree it's an added part to fail but I am pretty sure the relay circuit can have connections than the factory circuit.

I see the first point, high current through the radiator switch might lead to it failing? As far as the voltage drop you can wire the current circuit with a wire from the alternator post without a relay eliminating all the wires to under the dash and back.