I'll be the bad guy here and suggest that if you had engineered the swap correctly in the first place, you wouldn't be having problems. The correct way to do it would have been to modify the core support so that you could have mounted the radiator slightly forward and used an OEM engine-driven fan and a close-fitting shroud. I've seen way more electric fan installations that didn't work than I have seen that did work and the ones with the fan in front of the radiator are the worst of the lot. The factory makes electric systems work, but they have highly-paid professional engineers who know how to do it.
And in the name of all that is holy, please guys, stop installing these fosdick 160 thermostats, hoping that they will cure your improperly engineered mess. Motors need to run ~195/200 degrees in order to burn off acids and other by-products of combustion that pollute the oil. Take a tip from the OEM's. Did you ever see a 160 thermostat installed from the factory????????????