Reprinted from i Saluti, June 1996
This article describes replacing the inefficient engine-driven fan in a '67 Duetto with a thermostated electric fan. Although the car modified is a Duetto, it is similar enough to the modern Spider (or Bertone GTV), that most of the discussion applies. There is one exception, however, I used a "pusher" fan that mounts in front of the radiator. If you have an air conditioned car, you need to install a "puller" fan that mounts between the motor and radiator.
Alfa installed an engine-driven fan on all of its Spiders through at least '88. There are a number of advantages to replacing this fan:
I used a 1050 cfm 7.5 amp pusher fan from JC Whitney (gasp). The fan is 11 1/2 inches tall and cost $63 (#38DF0398U). Generally, any pusher fan that fits and is designed to provide enough cooling capacity for a 4-cylinder engine should work. (It's called a pusher fan because it mounts in front of the radiator and pushes air through the radiator.)
Electric fans generally come with a kit that lets you attach the fan directly to the radiator using plastic spikes. Don't do it, you'll shorten the life of your radiator! Instead, attach the fan to the chassis using the available framing in front of the radiator. To do this I constructed two mounting struts from extruded aluminum channel. See Figure 1.
The top of each strut is attached to the bottom of the upper crossmember that is located directly in front of the top of the radiator. The bottom of each strut is attached to the lower crossmember located directly beneath the radiator (see Figures 2 and 3). If you can't find suitable extruded aluminum channel, you might try using aluminum angle. Even aluminum angle sold as shelving supports, available from building supply stores, should work. Almost anything that is long enough, is relatively light, straight, and has rigidity should work. Depending on the fan's configuration and the car you're installing it in, it may be easier to fabricate brackets that attach to the chassis on either side of the radiator. I used side brackets to install the electric cooling fan in my '78 Spider.
The fan is attached to the struts using four 10-32 3/4" flathead screws and rubber spacers that come with the fan. The spacers decrease vibration and allow adjusting the distance between the fan and the radiator. I used one spacer per screw to set the fan back 3/8" from the radiator. Adding spacers would decrease this distance. Mounting the fan too far from the radiator will result in less air flow through the radiator core and hence give less efficient cooling.
It is important that an electric cooling fan be turned on automatically when coolant temperature reaches a predetermined level. On cars that come from the factory with an electric fan (Alfas at least), the fan thermostat is mounted very close to the water outlet at the bottom of the radiator. This makes sense since you really want to control the temperature of the coolant as it enters the engine block. The temperature of the water entering the radiator is really unimportant. So, the fan thermostat should be mounted as close to the radiator's outlet as possible. But surface-mounting the fan thermostat on the metal next to the outlet seems like a poor idea, since the radiator's skin temperature will only roughly reflect coolant temperature. It seems that the only method of accurately measuring coolant temperature is to cut the radiator and mount the fan thermostat so the thermal sensor is in direct contact with the coolant. A radiator shop, when asked about adding a thermal switch fitting to the bottom tank of a radiator, said that it would not be difficult and cost about $20. This seems to me to be the best way to go, to do it as the manufacturers do. Having said this, I did it differently.
To control the electric fan, I built a simple electronic control box mounted inside the car that uses a solid-state temperature sensor to determine coolant temperature. The control unit turns on a 20 amp relay that energizes the fan.
To mount the temperature sensor, I drilled a hole in the bottom of the radiator and soldered on a 1/4 inch compression fitting. The sensor fits into a 1/4 inch copper tube sealed at one end that is installed in the compression fitting. See Figure 4.
Whatever thermal sensor you decide to install, it's probably a good idea to mark the radiator for installation of the fan thermostat while the radiator is still in the car to make sure there aren't any clearance problems.
Based on a couple of Alfa models with factory-equipped electric fans, the fan thermostat should be set at 85 C (185 F). Both the Alfetta and Milano have the fan thermostats set to turn on the electric fan at 85 C. (That these values are the same is probably due more to parts availability than engineering design.)
Cooling Data for Electric Fan-equipped Alfas
Engine cooling thermostat Electric
Model starts to open fully open fan turns on
'75 Alfetta 88 - 92 C <= 100 C 84 - 88 C
'87 Milano 81 - 85 C 95 C 84 - 88 C
