First road trip analysis for the Mustang (update 8/21/18)

[Barry_R]

I would reconnect the bypass.  I wonder if that thermostat alone is restricting flow compared to the pump output.

[Stangman]

Don’t Chrysler have a thermostat that is the same size as ours only the center
Part that opens is bigger. I’m thinking maybe the one for the 440s. I have a griffin
Crossflow with two 1 1/4 tubes but with the two 11inch fans. Do you have the frame notched
on one side or did you get the big radiator and have to notch both sides. If you did maybe that single fan ain’t enough to pull the full length of the radiator, I believe that core alone is 27 inches.

[Katz427]

 When someone would come in and we would find the upper hose collapsing, or trying to, the head of the shop would first replace the radiator cap, as another response said. If that did not solve the problem, then he looked for a restriction, usually a plugged radiator. I remember one time, I pulled the radiator on a 1966 Mustang, (radiator looked great) and found that the coolant had turned to "jello" in the bottom tank. Only saw that a couple times in cars that sat around alot. Something is restricting flow, Barry might be right about running the bypass.