After working on the design of Geo-phys equipment I can say that for me it's not "a heat thing", but "a magnetic thing".
Streams and stones make small deflections in the earths magnetic field. Sensitive muscles could react to this too.
I ain't poo-pooing dowsing. I just wish they'd accept the real explanation for what they sense. I have to have a well bored in a few weeks time, for which I will need a dowser.