An electric fan has got to be the best solution.
Depending on where you live....Moss Europe certainly do a full bolt on electric fan kit called Revotec, that puts a solid state thermal sensor in the bottom hose. (they also offer other sensors that can be screw fitted into the radiator) I have the kit on my TR3 and it works a treat. In stop/start London traffic the engine stays cool and smooth running. The fitment is simple on the TR4 with all that underbonnet access. Your car needs to be negative earth for this kit to work. Not hard to convert your car if it is not.
link to site
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=8064
An electric fan will give you maximum air flow when needed and shut off when the temp is right. No power drain on the engine when not working, whereas the standard fan continually absorbs engine energy.
We can of course now enter the harmonic balancer conversation and crank breakages on 4 cyl TRs.
Let me say, my brother and I have continually run numerous 4 cyl TRs since 1970 and not yet broken a crank. Every one of those cars had the standard engine fan replaced by and electric one, as the first modification. In those days we made our own from wiper motors, exhaust clamps and Ford Escort plastic fans. Some of those old 4 bladed metal monsters are still in a box under our garage bench awaiting a concourse rebuilder's request.
Cheers
Peter W