k5 bad heater

[65truckowner]

My sons k5 blazer heater is not working as it should. It has a new heater core and the engine warmed up is just under 210. The heater hoses are hot enough that you cant hold them for more than a couple of seconds. One thing is the hose coming from the intake is smaller than the return hose for some reason. The intake hose has a crimped fitting that threads into the intake so I cant just swap them. I put a nut inside the larger hose and clamped it to see if it made a difference but it did not seem to help. Any ideas.