Harold - why would they have made these trucks standard with no heater if it served a vital purpose other than heating the cab? the use, or not, of a heater should have zero effects on the functioning of the engine
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics
