Fan not running

[yoda]

My wife and I just got back from a 10 day run, and put 2600 miles on the bikes. I noticed several days ago, a gurgling from behind the right side cover, after we stopped. I had topped off the coolant reservoir before we left as it was low. I figured it was just because I had the notorious loose clamps and o-ring. I got some coolant, but was noticing that the fan was not coming on. Definitely a concern, as the temps were upper 90's plus, and there were several times we were sitting in traffic. I shut the bike off when I could, and over the past 800 miles, needed to add about a quart of coolant. I never saw it leaking/dripping, so my assumption is that without the fan coming on, it is cooking out the overflow in a way I am not seeing it. But to go through a quart, I would think I would see some evidence of it.
So what is the best way to start checking for why the fan isn't coming on? I did check the fuse, and it is fine.