I got myself in this situation because I decided to go with spring clamps. I figured all new hoses (old ones were from 1998, newest date I could find) and new spring clips would be a good combo.
All of my rad hoses were the same OD (nominal) upper and lower, both ends. Maybe OE added thickness to the lower hose???
I am guessing that the OE bypass hose is significantly thicker than the Gates hose for the supplied clamps to work. Once I get the McMaster clamps, I will drain the system change out the clamps as needed and see what works.
I am 99% sure the 1.5" clamps on the upper rad hose will solve the thermostat cover leak.
