About 5200: "Heat resistance - Due to the decreased value in bond strength at elevated temperatures, we do not(nl)recommend use of this product above 190°F"

The engine compartment should not exceed that, but on a very hot day and after running a long time it might get close, and I really don't want that pump to pop off and have to clean up old hardened 5200 before going to plan B.

I'm thinking JB Weld now. It is rated to exceed 500°F.