Otto, IIRC the original 1951 heater hose inner diameter was 5/8". On my '51 with a '54 235, I use 5/8" and 3/4" as the later water pump hose nipple is durn near impossible to get the 5/8" hose on. Get about a 6' length of each and you can cover all potential size issues. Oh and some new hose clamps may be in order depending on how yours are.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
