Some had good heaters, others, not so good. The ultimate problem is that you're in a metal box. Placement and maintained and/or reliable heater fans mattered a lot, as with the ever reliable SW 1500's, which kept you warm from the waste down with a well placed fan blown heater, and your jacket kept you warm from the waste up, hanging out the window taking signals...

About 4 o'clock in the morning, on a December night, even in Sou Cal, it's cold. I've worked just below freezing at night, on Beaumont, but can't imagine what you poor SOB's on MRL have to deal with. I can't count the number of times that I worked an engine with no operating heater fan, and that really sucked. I always brought an extra down vest, and/or sweat shirt, to layer up if needed, in my grip.