What size...? Barb or bubble? I think I hit >100 psi on my rigged up A/C manifold that was a 3/8 hose on a barb and a worm clamp. It usually lives under 50 but it spiked for some reason. Obviously the hose isn't a 1 7/8 radiator hose on a bubble flared radiator spud but those smaller hoses reduce the pressure at the clamp. Just sayin a heater core should not fail at <50 lbs unless its paper thin from internal corrosion.
