i haven't heard of anyone adding a second radiator, just relocating the original.
http://www.moto4less.com/GA-RADY660-p-atv-radiator-kit.html

http://www.extremesnorkels.com/products/Yamaha-Grizzly-660-Wild-Boar-Radiator-Relocation-Kit.html

and temp gauges
http://utvinc.com/yamaha-rhino/lighting-electrical-gauges/utv-inc-black-or-silver-water-temp-gauge-kit-1/
http://www.anfittingsdirect.com/product_info.php?products_id=801
and fittings
http://utvinc.com/yamaha-rhino/lighting-electrical-gauges/utv-inc-1-8-npt-inline-water-temp-sending-unit-housing-1/

and a good write up on the install
http://grizzlyriders.com/forums/electrical-electronics-lighting/39-atv-water-temp-gauge-t-fitting-nordskog-performance-j-t-products.html

 

If you're going to add two, I'd think it should go from engine to top rad, top outlet to stock inlet, and stock out back to engine. I've never heard of anyone else doing it but that seems to make pretty good sense. To me at least. lol

 

another option is an auxiliary oil cooler. Gunny made his own, complete with a dual filter set up, but you can also buy a kit on ebay for around $100

 

So between adding a 2nd radiator and a "GunnyCooler", does that mean that we're ready for this heat wave finally???

My Spyder sat out in the Sun yesterday afternoon and the thermometer display was reading 111 degrees!!!

 

Bob, you been riding that spyder much?