Plugged the block heater in on Sunday evening. Monday AM temp was 43*f , truck started easy & idled quietly. Had some heat immediately. Last night I did not use the heater. Started OK, but much noisier & took about 6 miles of easy driving for the temp gauge to move off the cold mark. Ambient temp about 42*f on startup. I am sure that using the heater will make a huge difference to fuel mileage too (Not too sure what it will do to my utility bill, though. :--) )