I think mine has started at -20, but if it is that cold I give it a snort of starting fluid after the plugs stop cycling the first time just in case because I am usually walking a long ways if it doesn't start.
DO NOT DO THIS IF YOU HAVE NOT BEEN SHOWN HOW!!!
If it is at the house it gets plugged in so the oil gets warm when it hits the block and the IP and filter have a little radiant heat.
There is a big differance between -60 and -40, propane goes liquid at about -44 most anti gels stop working at about -50, starters slow down enough so there are not enough RPMs to start. Anybody know the differance in battery output. 15W-40 oil viscosity is such that it acts like glue when pumped into the engine. I do not run my schoolbus when it is colder than -30, to many things break and I am out in the hills with a load of other peoples kids. Chopping through a couple feet of ice so the cows can drink warms you right up.