by Dan Cameron

There have been many articles written on the subject of how to get the Tiger to run cooler, but in spite of all the little tricks, some of us continue to flirt with the other side of the 200-degree mark. This is particularly true for those who have modified engines which directly add to the under hood temperatures.

The key is to maximize the heat transfer out of the radiator. Larger and/or more efficient radiator cores and louvered hoods to increase the airflow through the radiator are a start, but on those 90-degree plus days, while idling in a line of traffic, the old needle creeps up. I personally experienced this problem when a new engine was installed in my Mk I.

All those mega-bucks spent on engine performance converted themselves directly to horsepower and heat. Even with a six blade, high pitch fan (no louvers) the problem persisted.

A rather simple and inexpensive solution was to install an auxiliary fan in front of the radiator. The additional airflow greatly improved the capacity for heat transfer. After evaluating the world marketplace, I found there are about as many fan manufacturers as there are Tigers. For our applications, the flat pan motor design is best due to its thin front-to-rear thickness (about 2.5″) minimizing clearance problems.

Now, a word of caution. Some of the units have fan blades that are not as rigid as others and have a tendency to flex. This happened to one of our friends from CAT on his way to the United at Indy. At highway speeds, the blades were pushed back into the radiator core carving out a perfect circle of leaks! The fan I chose is manufactured by Derale Oil Coolers, Fountain Valley, CA., model number 902. It is 12″ in diameter, thermostatically controlled, compact and rigid. In addition there is a manual over-ride switch so that the fan can be turned on for full time operation when desired.

The installation instructions are pretty good except that the wiring diagram provided with my unit was wrong, resulting in a number of blown fuses before the problem was isolated. The wiring diagram on the box shows a cartoon of the wiring and the two-position switch. The problem was that the switch was upside down in the drawing resulting in the power line going directly to ground and zapping the fuses.

Installation tips:

Detach the fan blade from the motor and reverse it. Remember that we are mounting the fan on the front side of the radiator and pushing air through it. Most fans are shipped with the blade installed so as to pull air through using a mounting behind the radiator.

Be sure to place the thermostatic sensing unit on the left hand (driver’s side) radiator tank. This is the hottest side and will provide better operation.

Run the wire leads to the thermostatic sensing unit through the firewall parallel those going to the left hand headlight and horn.

For an added touch, go to the local junkyard and strip a late model wreck of its corrugated plastic wire covers. This will keep the engine compartment neat and the wires safe from abrasion.