R1NGA, very nice work.
Just food for thought, it's been my experience from streetrods that when mounting fans, they should be run through a separate relay. This allows for the switch / signal wiring to be run at low amp draw while the relay is being supplied by a fused direct wire from the battery or other high amp location that is keyed on and off with the ignition.
In doing my research for an overheating blown 392 hemi, I found that all the major brands, I ended up with Spal, pulled about 1 amp per 100 cfm.
In your case the fan is probably only pulling about 400 to 500 cfm as it seems to be usable on a 4 amp fused circuit. That's not a lot of air, but anything is better than what you had when you started.
So in my case with around 3000 cfm from two 11" Spal fans, I wired in a 30 amp relay and ran both fan motors from the single relay fed by a 10ga wire. I was at the Indy's Nationals and we were in parking lot traffic and my fans quit. What I found out was that my two fans pulled over 30 amps and my relay fried, read melted. In the hotel parking lot I converted over to two 30 amp relays and ran one for each fan motor. This proved to be the right way to go and it worked great from then on.
Here is a typical "kit" for fan power and coolant sensor for a streetrod. It comes with a circuit breaker in lieu of a fuse.
Here is a wiring schematic that is commonly used for wiring in a relay for any requirement needing a relay, mainly used on electric fans though.
Here is the pin out on a typical relay with internal circuit shown.
These relays can be purchased at about any auto swapmeet with the plug and wiring pigtail for around $5 each. I always have a few sets around the shop just in case I need one.
I would just double check the wiring on your fan after it's been running for a few minutes. If it's getting warm, I would go the extra step and install a relay for a separate power source for the fan. You can still use the same wiring control setup you have now, just to the relay instead of the fan.
I would also just check to make sure you're not just blowing air into the under bonnet area without any means to exhaust the air or you will not get any circulation. Likewise on the blow towards the motor; if you're pulling a negative pressure under the bonnet you're just cavitating the fan so to speak.
Again, nice work.
