Not sure if I should put this here or another thread so if anyone thinks it needs moved, knock yourself out
I finally got around to mounting an electric fan and taking off the stock metal fan with clutch. I used a fan off some random car in a junkyard that fit pretty well. I haven't put a temperature switch on it yet but being winter time means I can get away with not having an automatic fan for a while. Since it takes a bit of work to swap fans it isn't really practical to do A-B-A testing. The only thing I have against vans are they are a real pain to do any work to. It took me 30 minutes to remove the fan and shroud using air tools, probably a 5 minute job to a normal car.
So I have been driving it enough with the MPGuino mounted to get a good feel for it's mileage and it is pretty consistently at 18.5mpg for a standard ~50 mile drive I typically do. But having driven it for a few days with the fan removed and the electric on a toggle to use when needed my average mileage is now 21.3 for that same drive in similar conditions. So for this I would say a 2.8mpg gain with maybe a 0.5mpg error at most due to the lack of A-B-A testing done all on the same day.
So either the fan clutch was slightly bad and making it get worse mileage or belt driven fans in general suck. The clutch feels about right when turning the fan so I don't think it was bad. The noise from the fan moving air all the time is now gone so it is quieter to drive as well as it has a bit more power and the engine revs faster now. I never liked belt driven fans before but now that I have a way to actually measure the result I don't think I will ever leave one on a car I own again.