I started my 04.5 duramax at -40F no problem. no way to plug in the block heater, it had sat out for 10 days with highs near zero, lows in the -25 to -40 every night. turned the key waited for glow plug light to go out, turned ignition off, then on waited a second or so for glow plug light to go out, started right up. smoked a bit and rattled, but started no problem.
actually started far better than a 1960's vintage gas engine would at those temps!
Now warm up time, another story. the trip was downhill for about 15 miles, even with tow/haul on getting heat was a LONG process! Thank god for heated seats!
A far cry from 30-40 years ago when diesels were tough to start below zero.