Have an 05 (I think) grizzly 660 4x4 ultramatic. Ran hot on me one time a couple weeks ago. Parked it looked it over and seen the reservoir was empty of coolant. Filled it up and fired up the atv let it run and got the air out then got it to cycle water. But the water is leaking from a broken fitting on the tstat housing that has a small rubber hose running back to what I believe is the water pump. I'm not atv tech savvy so any help would be tremendous. Is this hose necessary can I plug the broken fitting off or should I try and fix it?

 

Almost certain to be a thermostat by-pass hose. When the engine is cold the water can't circulate as the thermostat is closed, the hose allows some water to flow back to the pump. As the engine warms, this flowing water gets hotter and the thermostat opens. Without it, cold water is trapped under the thermostat, so the thermostat doesn't open, and the water round the engine overheats. If the casting is expensive, any engineering firm will be able to save the old one by drilling and tapping the hole and fitting a screw in hose fitting.

 

That could be a sign that the coolant has never been changed. Probably needs new hoses, and a flush, then new 50/50 coolant.

 

Very hard to tell from the pics but go to somewhere like partshark and look up the OEM parts for your year and Grizzly 660. I looked under water pump and that is what it appears to be but again, hard to determine from your pictures. If that is the water pump, that hose is the weep hole for when the water pump mechanical seal fails and will need replacing. Obviously you would do a coolant flush at that time too.

The mechanical seal is meant to keep coolant from mixing with oil so if it is failed, you will want to replace it right away. Coolant out the weep hole is a clear sign of that seal failing.