Quote Originally Posted by 34_40 View Post
My first reaction is that you used a cheap poppet style thermostat.. if you did, replace it with a sleeve type. The sleeve type will flow more and maintain an even temperature.

I'd also try to get the fan into the shroud opening more. either add more spacer or add to the shroud??
I'm tracking with Mike. My first thought was a sticking thermostat, hanging closed until the higher than desired temp can generate enough force to clear the interference. Also, like Mike says, the fan needs to be into the shroud at least 1/2 way, and ideally with only about 1/4" to 1/2" of blade on the outside of the shroud opening, and OD clearing the shroud opening not more than ~1/2", depth being just as important as "fit", IMO.

There are a lot of people that agree with your assumption that an electric fan is going to be more efficient than your mechanical, but I do not agree. With an aftermarket electric you will have more restriction at speed than a well fit shroud & fan, and while it doesn't seem logical the amount of electrical "work" required will load the engine just as much as the mechanical, and the mechanical fan will actually "coast" when the clutch disengages at temperature while the electric may still be energized. Your increased alternator load will require as much, or more power than your current fan. My advice is stick with the mechanical fan, replace the thermostat first, and then if that doesn't fix it look at the fan/shroud clearances.