On 12/27/2009, Dave Tustin in Sandy Hook, Manitoba, Canada wrote:
"Electric fan for my MGA. - Should I remove the engine fan or leave it as backup? Is a simple on-off switch sufficient or should I install a temperature sensor"?

First I should ask why you want to fit an electric fan.

For performance reasons, fitting an electric fan allows removal of the mechanical fan, thereby freeing up multiple horsepower at high speed that would otherwise be used to run the mechanical fan. It can also reduce fan noise substantially at road speed (assuming the electric fan is not too noisy). I have installed an electric fan on a couple of cars (not MGA) for those reasons, and the results were quite good.

I would always use a thermostatic switch that would only run the fan when coolant temperature was above a set threshold. In one case I used an illuminated push button switch on the dash that would light up when the fan ran, and could be switched on manually if you wanted to. If you can hear the fan run then the lamp may be redundant and unnecessary. If the thermostatic switch works properly then the manual switch is generally redundant. Lots of new cars have electric fans, and maybe none of them have manual switches. If the engine is cooling properly with no mechanical fan running then there is no need to switch on the electric fan.

Thermostatic switches are available in different types. The common ones supplied with aftermarket fan kits often have a thin rod sensor that can be pressed front to back through the radiator core. These are most commonly connected to a relay the will switch power for the fan. The setup will usually have an adjustable threshold for the switch point. It is common to install this type of sensor in the radiator core just below the upper radiator hose port where it will be sensing temperature of the hot fluid as it comes from the cylinder head. In this case the switch point should definitely be at least 10 degrees (or more) higher than the temperature where the thermostat will open. There is no sense running the electric fan when the thermostat is trying to restrict fluid flow to increase coolant temperature. If the engine cools well enough at 10 degrees above the thermostat rating, then you don't need the fan to be running. The fan is needed if the coolant temperature continues to rise significantly higher than 10 degrees above the thermostat rating (or whatever you may think is too high). You might run a 180dF thermostat and set the fan switch on point at 200 or 210. If I was retaining the mechanical fan I would set the switch point quite high and hope it never needs to switch on.

I tried an electric fan with that type of sensor and relay for one summer in 1994. I did it primarily for trailer towing at express speeds, or in case of having to stop or move very slowly after a hot run at speed. It didn't make much difference at high speed on the road. I used to remove the relay to disable the electric fan while autocrossing with SCCA, as it was not allowed in Stock class. After one season I removed the electric fan (next time I had to R&R the radiator), and I never bothered to reinstall it (mostly because it added work to maintenance chores).

In Spring 1997 I installed a fan shroud, just before the Alaska trip, and before spending lots of time in Texas in June and July. The fan shroud does a wonderful job of keeping coolant temperature under 220dF with the worst cooling conditions (slow speed in hot weather), so I have never had a yen to install an electric fan again on the MGA.

Many years earlier (1971-1974) I had a kit car with mid engine V8 and front mounted radiator. That used exclusively electric fan and thermo-switch in the lower radiator hose. It worked fine. In 1972 I installed an electric fan in a new Ford Pinto with 2-liter OHC engine, thermostat in the lower hose, and removed the mechanical fan. I was very happy with that set up. Fan noise at road speed (and during acceleration) was cut dramatically, top speed of the car increased by 5 mph from 110 to 115 mph, and 0 to 60 mph acceleration improved noticeably. Furthermore the electric fan almost never ran.

Expect 30 degrees (or more) difference in coolant temperature from top to bottom of the radiator. With thermo-switch in the lower hose it was set to switch on at 160dF. The idea is, you should be more interested in the temperature of coolant going into the engine than what comes out. If it's cool enough at bottom of radiator, why would you care about coolant temperature up top? In cold weather temperature drop from top to bottom might be huge, and you certainly don't want a fan running then. The thermo-switch I used in the lower hose was a high current switch (like a brake light switch), no relay needed, so wiring was very simple.

MGA with modern style radiator core are commonly touted as having inadequate cooling, running undesirably high temperature in warm weather. It is my personal opinion that most of these cases are over blown, as "too hot" is a relative opinion. It is also my impression that MGA did not used to have cooling problems (when I drove them regularly in the late 60's). They never ran above 190dF in hot weather, and ran so cold in sub-freezing temperatures that I had to block off most of the radiator core with cardboard to make the heater work. Original MGA radiators had convoluted cell core, while modern cores have flat water tubes.

If you think your MGA has inadequate cooling, too high coolant temperature, then the electric fan may or may not help, but removing the mechanical fan may be counter-productive. You might install the electric fan first to see if it makes any significant difference. If it appears to reduce coolant temperature by at least 10 degrees in hot running conditions, then you might try removing the mechanical fan to see if the electric fan can handle it alone. An electric fan should produce adequate air flow for cooling while standing still. No fan should be needed for running at normal road speed.

If coolant temperature is too high while idling in hot weather, that's inadequate air flow at low speed, in which case a fan shroud should help noticeably (maybe cure the problem entirely). Electric fan might help too, but if the fan shroud works as expected you don't need the electric fan.

If you have reasonable coolant temperature when traveling at 50-60 mph, but temperature increases noticeably with increasing road speed, that is indication of inadequate air flow through the radiator core at high speed. Electric fan may not cure that problem. Solution for that might be to vent the engine bay through the inner fenders into the wheel wells (although very few people ever do that). More commonly people try to open up the slats in the grille. Installing a radiator core with too high density (too many fins and tubes per inch) can restrict air flow enough to create this problem. If the radiator core itself is restricting air flow at road speed, then maybe the only cure might be to recore it with a lower density core with more air flow area between the fins and tubes. I suspect this is why the original cell core radiator worked so well, lots of air flow space through the core.

Another solution might be a physically larger radiator. These days some people install a (very expensive custom built) very thick all aluminum radiator, most commonly with an electric fan. They usually swear it works great, but in most cases they never tried an electric fan with the original radiator. They can also never explain why an aluminum radiator might be better when copper conducts heat so much better than aluminum.

Quite recently I have seen an electric fan setup for MGA using two 9-inch pusher fans side by side. It looked to me like it might work quite well. In any case if I was to install an electric fan(s), I would expect to remove the mechanical fan for improved performance. I see no reason to have both mechanical and electric fan on the same car. If it doesn't cool properly it probably won't make much difference if the fan is mechanical or electric, and being redundant likely won't help much either.