Yep, those can tend to cause a bit of overheating too. Funny thing, had a customer with a newer JD excavator that was having some heating issues last summer. He'd always call from a job in the middle of nowhere when it happened and ask what I thought the problem was. Tried troubeshooting over the phone having him check various things as he was trying to prevent having to prevent me coming so far to get to him ((((ie save money when things were really tight already)))). All of that really got no where, as you'd expect, but finally winter hit and the problem went away. It finally started on him this past summer and all but shut him down. I wasn't avaialble to go look at it at the time so he got someone local, who was recommended by someone at the job site, to come out. The machine had a serpentine belt on it and according to what I was told when the guy checked it, it was tight, and had never made any sound at all. The guy he called installed a new belt, blew out the radiator (something I had already had the guy do long ago) and the heating problem stopped.
I've never heard of a serpentine belt slipping enough to cause the fan or water pumpo to slow down and never make a sound. I have seen something similar on this same customers T190 Bobcat after he replaced two alternators and then brought it to me with a charging problem. Batteries checked OK, alternator checked OK, and the V belt driving the alternaor was tight and made no noise, but was a bit aged and cracked. Replaced the alternator belt and he's had no problems since. In the end the problem isn't always obvious and I guess you learn something new everyday.