There are a few reasons that you may be experiencing a leaky hose after a new clamp install:
The hose is not properly compressed. A hose that has been previously clamped will have a witness mark or groove on it from the original clamp. When you install a new clamp on a used hose, it will not compress the hose properly due to indentations on the hose from the original clamp – usually resulting in a leak.
You may have selected the wrong type of replacement clamp. Attempting to replace an old clamp with a new clamp that is too wide for the channel will not only crush the beads on the outside of the channel, it will result in a poor seal.
For example, you should never replace a constant tension clamp with a worm drive hose clamp. Constant tension hose clamps come in many varieties, with one thing in common: they are designed to keep constant pressure on the hose in temperature extremes. Replacing a CT clamp with a WDHC is just asking for a leak or breakdown.
Improper placement of the clamp on the hose. Rubber hoses that fit onto a connection with a bead require the clamp to be in the right place. The clamp should be right up against the bead on the connection, however not on it. If the clamp is placed farther back, it creates a small crevice behind the bead. The chemicals in the coolant will deposit in this crevice and begin to corrode the metal connection. They will actually erode metal and the next time a hose is replaced, it will not seal due to corrosion forming or “crevice attack.”
Overtightening the clamp. Many failures and leaks are caused by overtightening the clamp. This can even cause complete clamp failure during the initial installation. While we realize that most people will not use a torque wrench when installing clamps, please refer to the torque specs we recommend, based on the type of clamp.
You installed it on a used hose. When you install a new clamp on a used hose, it will not compress the hose properly due to indentations on the hose from the original clamp. This usually results in a leak because the hose is not properly compressed. Always replace rubber hoses and clamps together for the best job and to reduce the potential of a comeback.