I run into this all the time at work on our fleet of school buses. The hoses do not change in size at the same rate metal does when it gets cold. To cure it for good, replace the screw clamps with spring clamps. The spring clamps apply the same amount of clamping force no matter what the temp is out side, screw clamps stay at the same size even if the hose doesn't.
Tightening the screw clamps will also work, just tighten them while they are cold or till the leak stops.
Joe
Seen the the same thing many times when it gets real cold.
