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1955 Ford Part 80: Thermostatic Switch for the Cooling Fan

Updated: Dec 27, 2019

Thermostatic Switch for the Cooling Fan


Back a few posts ago I mentioned a slight problem with the cooling fan switch and what I had decided to install to help resolve the issue. You may recall that the car does have a stock “Magicaire” heating and ventilation system plumbed from the engine to the firewall controlled by a small array of levers and cables on the dash that route to air passageways. The installation of these vent tubes, doors, and other assemblies are all covered in detail among other posts so we will not dwell on them here. The issue I was experiencing was simply this: unless the dash temperature control was set to “High” the cooling fan would not turn on. Examine this photo:

A "T" fitting for both the heater hose and the thermostatic switch didn't work!

Ford’s original cooling fan was a simple affair – a belt driven fan that bolted to the water pump, driven by a pulley that was in line with both the generator and crankshaft dampener. Since I had installed air conditioning I thought it best to upgrade the radiator to a 4 row unit and to use an electric fan. Doing so necessitated some type of a switch that would send a signal to the fan to turn on (and off) as needed. Most of the time when these aftermarket units are installed, people will use a relay and thermostatic switch that grounds the lead from the relay when a pre-set temperature is reached. You can see that a long time ago I installed a T fitting at the original location of Ford’s 90 degree elbow that routed coolant to the heater core on the firewall. (Some of the cars had a vacuum operated valve installed in this location on the intake manifold, but the Fairlane here has an upgrade in a slightly better system where the valve is installed on the firewall itself and controlled by a lever and thermostat coil under the dash.)

The problem I had was not the switch, wiring, or the relay. You can see from the T a few pictures above that I placed the switch in the same location as the line that goes back to the heater core. When the temperature control lever on the dash is set to High, coolant flows back to the heater core and thus affects the thermostatic switch either engaging or disengaging because of the temperature of the coolant. When the temperature control is set to Low, there is little to no coolant flowing past the switch even though the coolant temperature was high enough to where the cooling fan needed to kick on.

I considered several options and even tried a few of them, but none of the options I tried resolved the problem. I tried placing the 90 degree on the water pump port, and vice versa with the thermostatic control switch. Some helpful soul suggested drilling a hole in the intake and tapping a new port for the switch. One option I considered was a means of putting the switch inside the upper radiator hose, but I could not justify the added expense, cutting the hose, cluttering up more right above the engine, etc.

Then a suggestion someone made on an internet forum really got my attention. The solution is pictured above in the title but is posted here again below.

I chose this temperature switch controller not only as a solution to the plumbing and wiring issue, but also because the temperature at which the switch would engage would now be adjustable. Wiring the new switch was very simple, as the idea was to use the controller to ground the lead for the relay. Only the ground lead from the fan relay was needed since the unit itself has no need to be powered. The capillary tube that senses the heat was fastened to the radiator like the instructions pictured and away we went.

The subsequent work on the carburetor and the transmission overdrive placed this update on the temperature controller in the shadows. However, over the last few months the controller has worked extremely well in mild or hot weather, engaging and disengaging the cooling fan as needed. Yep, so far this summer I have been very impressed by the new switch. If you are considering adding this feature to your car just make sure you purchase a unit that has a dial. There are many listings on eBay or in other online stores where the switches are sold without a dial. While the dial is not going to match your temperature gauge under the dash, you can do the math on the difference between the two and adjust accordingly.

the Hot Rod Reverend

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