Picking out the right radiator hoses for any engine swap application is a matter of trial and error. We picked up a set of hoses for a 429-powered '76 Ranchero from the local parts store to get us in the ballpark. Tried-and-true methods, like bending up a piece of coat hanger to use as a template at the parts store, work just as well.
The $50 Mark VIII fan we scored off of eBay was pulled out of a '98 Lincoln. It arrived a bit dusty, but was in otherwise excellent condition. We gave it a quick cleaning and degreasing before dropping it into the car.
Mark VIII fans have three wires that power the motor. On two-speed versions of the fan, one wire activates low-speed operation, another wire activates high-speed operation, while the remaining wire serves as the ground. On one-speed fans such as ours, the outer wires work as the power and ground, while the center wire is a dummy that serves no purpose at all.
The aftermarket abounds with both screw-in and probe-style thermostat switches that turn fans on and off automatically at different thresholds. This Derale unit will turn our Mark VIII fan on at 180 degrees, and turn it off at 165 degrees. We matched it up with a 160-degree Summit thermostat. In a healthy cooling system, the cooling fan controls how hot an engine gets, and the thermostat regulates how cold the motor gets. Hence, it's important to select a thermostat that opens up below the cooling fan activation threshold. If the thermostat opens at a temperature above the activation threshold of the fan, then the fan will run continuously regardless of how well the radiator dissipates heat.
The only real drawback of the Mark VIII fan is that it draws a hungry 30 to 40 continuous amps, and can momentarily spike up to a 100-amp draw at startup. The easy fix is a high-capacity relay, such as this 70-amp unit from Dakota Digital. To put this into perspective, many aftermarket fan controllers come equipped with 25-35 amp relays. High-capacity relays such as the Dakota Digital unit may be hard to find at the local parts store, so we tracked one down on eBay.
Power hungry fans can quickly drain a battery if the alternator isn't up to snuff, and that's definitely the case with the Fox Mustang's puny 75-amp unit. We replaced it with a Ford 3G alternator out of a SN95 Mustang rated at 130 amps. It features an internal regulator and cooling fan, and runs cooler than the stock unit. The 3G alternator comes in both small- and large-frame designs, and is a very popular upgrade in older Fords. We picked our rebuilt 3G alternator up on eBay for $40.
For extra insurance, we poured in a bottle of Purple Ice coolant additive from Royal Purple after dropping the radiator in place. This synthetic additive reduces engine temperature by lowering the surface tension of the radiator fluid for improved heat transfer. It's compatible with standard green coolant and GM Dex-Cool, and lubricates seals. In applications that run straight water, Purple Ice prevents rust formation too.
Derale recommends inserting the thermostat probe as close to the radiator inlet as possible. Positioning it too far from the inlet can cause the fan to turn on too late. The probe must be pushed in very gently to prevent damaging the fins.
The probe is held in place on the opposite side of the radiator using a small foam pad and a retaining clip. The excess section of the probe can be trimmed off if desired.
Before installing the Mark VIII fan, it needed a quick trimming. Like most factory designs, the Mark VIII fan uses mounting tabs to hold it in place. Since we'll be attaching it directly to the radiator, we cut them off with a jigsaw.
Dropping a big-block into a Fox chassis leaves very little space between the water pump and cooling fan. The shroud on the Mark VIII measures 5.5 inches deep. We trimmed it back using a jigsaw to 4.25 inches, which was the most material that could be removed while still enabling the fan blades to rotate freely.
The final step in modifying the Mark VIII fan was drilling holes for the mounting tabs and thermostat switch wires. We drilled a 3/8-inch hole near the radiator inlet through which we routed the thermostat switch wires, and drilled 1/4-inch holes at each corner, which will be used to attach it behind the radiator.