Do you let your old engine warm up or just get in and drive?

Not an old 440 but my Cummins yesterday I drove it for 20 miles and it never came off of low temp, it was 0 degrees but man was that thing a slug. I also stopped for fuel which took 15 minutes to pump 8 gallons of fuel, finally I said... close enough.
Sorry for the derailment ( I'm pretty good at it )