Just cruising along at 55 should not collapse the lower hose uNless he has a steep gear in it and the motor is really singing ...IMO.

I would LOOK at that situation ....try it ... but I am thinking the flow through the rad is somehow hindered. Many times I have seen and heard of the fan-action actually blocking air-flow at highway speeds.

Just pull the fan OFF when you take your next HWY-cruise ...and see what happens.