First time seeing this info in a convenient flowchart-style, thought it might be useful:

 

I guess when you're busting snow drifts up to the hubs, locked in low range and GPS says you're going half what the speedometer reads then that's "overdriving." I roll the windows down and use the heater core, but after a while it still gets close to 230 on the Ultragauge and I have to give it a break.

 

Generic chart, does not address viscous clutch and electric fan set up on our trucks, our wonderful gauges etc. Fot those who frolic in snow at slow speed, does your electric fan come on? I have always thought you should be able to have a switch and force the fan on, like when towing a trailer up a long grade, etc. 3rd grade was the long one for me, five summers passed.