I have a 2013 Polaris Ranger 500 EFI UTV. A while back I happened to notice that the electric cooling fan had kicked on and was running constantly. I checked my radiator, and it was low on anti-freeze. I topped it off and checked it again a few days later and it was low again. I have checked the radiator and hoses for leaks, and have found nothing. I checked the oil and it's showing some foam in the oil reservoir, but the oil does not seem to be milky. I can't figure this one out, and am wondering if any of you have an idea as to what the problem is.

Mine did that once. I had been running through a CRP field looking for a deer my nephew had wounded and lost. The front of the radiator was full of Johnson Grass seeds. Cleaned it good with a pressure washer, problem solved.

Mine is clean. The problem is elsewhere. I believe it's engine related. Maybe the head gasket.

Get out your manual and read up on how to bleed the cooling system. There'll be a little valve screw to turn. You have to get the front up on blocks. Mine's an 800 so it's not quite the same but it'll likely still have some air in it.
If that doesn't fix it, disconnect a fan wire and get it good and hot, maybe 220 or so. Then shut it off and start sniffing and listening for antifreeze leaks.

How old?

I'd replace the rad cap as it may be allowing boil off? Otherwise with no obvious leak, headgasket would be my first thought as well.

follow along all the hoses and look for dried antifreeze at each connection.

Well, if he doesn't have a blown head gasket now, he probably will have after doing a test like that....................................

220F isn't going to blow anything that's not in danger of blowing anyway. The fan on mine doesn't kick in until just under that, then it cycles between there and 195. You don't want it any hotter than that, though.

Had the same issue on a Rhino...bad thermostat. Antifreeze was blowing out of an overflow tube. Trashed the fan before we figured it out.