3.9L Cummins block heater question

[PHS79]

I did end up getting it started, I ran to the local parts house and got a can of "starting fluid". Just 1 quick little shot and the lift was running. We ended up using it for about 40 mins that day, I checked the anti-freeze afterwards and it was good to go. I plugged the lift in overnight, got to the job site the next morning, the block was warm to the touch. But with overnight temps of -5*F and wind chills of -20*, the old girl refused to start, she is a cold blooded SOB and needs to be plugged in even at temps around 30*.