Hi,
I agree with Bill about the sensor, put it into the coolant via some sort of connection. I prefer the coolant return line, measuring the temp of the coolant as it comes out of the radiator (i.e., the lower hose). The temps should be relatively stable there and that should turn the fan on and off at the ideal times. I also wouldn't rely upon the type that clips into the radiator fins. The type that slips under the end of a radiator hose seems to me to be asking for leaks, too. There are many different brands of sensors & thermoswitches, but they all do basically the same thing. I'd suggest one that comes on at no more than 185F and turns off at around 170F. There are some with higher ratings, many modern engines are designed to run hotter, but TR engines like to run cool.
Spal is a good fan. The 14" should work very well, some like to go as large as 16". I think the 11 and 12" sold by some TR vendors are a bit borderline, if used alone. Might be okay as a supplement to the stock fan, though.
I see
www.racerpartswholesale.com is carrying the entire Spal line, now, and seems to have competitve prices. There are other good brands out there, too, so you might check
www.summitracing.com, etc. Your biggest challenge is the thickness of the fan if you are mounting it as a puller, behind the radiator. There is little clearance with the cross tube between the spring towers. However, one Spal model is just slightly over 2" thick. Another, with slightly higher output, is about 3.5", which actually fits in my TR4 (same setup as your TR3 basically).
What are you planning to do about the original fan, hub, belt and pulleys? If you plan to remove them, I suggest a thin belt conversion with a harmonic dampener. The fan extension hub also serves as a dampener, normally. The extension can be left on, just removing the fan, to continue using the original belt and pulleys.
Also, do you have an original generator? If so, watch out for high amperage fans. The Lucas generator produced around 17-22 amps at best, and some fans use more than 10, 12, 15 amps themselves. Doesn't leave much juice for other things like the wipers, headlights, ignition system, etc.
I'm not sure about the Spal controller module. It's really designed for use with AC, I think, to kick the fan on at lower rpms as soon as AC is turned on. I guess it can be set up for lower rpm operation intially, even without AC, higher if engine temps begin to climb, so the fan might run a little more quietly. (Curved blade fans are generally quieter than straight bladed fans. However, some curved blade fans don't produce as much air flow.) I think a simple on/off thermoswitch is adequate. A controller box is just one more thing to go haywire, IMHO.
Are you having cooling problems? If so, I suggest going through the system pretty well anyway and not depending upon an electric fan to solve problems. It might cover them up for a while, but they tend to show up again eventually, usually at the worst possible moment.
BTW, my electric fan is hooked up with a self-resetting circuit breaker, instead of a fuse. That just makes sense to me. I'd hate for a fuse to blow and leave me stranded (although I usually carry plenty of spares).
Have fun shopping!
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