You might look to see if it's sucking the radiator hose flat;if so,you can run a spring down it to keep it from collapsing,or switch to a piece of pipe with a piece of radiator hose at each end to couple it to the radiator and the engine.
Speed

1954 GMC 350
1957 GMC 1/2 ton
1962 Chevy C-30
1952 Chevy 6400 dump bed project truck
'98 Harley FLSTC
'66 Pontiac Catalina
'76 Chevy 1 ton Duallie
'84 Bronco II
'78 Dodge W-200
'81 Toyota 4X4 truck