antifreeze leak behind water pump,whats going on ?
also it is a 1991 f150 with a 5.8l eng with 73000 or so miles on it
It’s either the water pump leaking or the timing cover itself. Coolant flows through a couple of passageways in the timing chain cover and with time, aged coolant, etc. the gasket between the cover and the engine block can rot out.
Even the cover itself can rot. It’s aluminum and chronic leakage in that area will erode the aluminum. It may be time for a new cover and if you’re that far in then a new timing chain should be considered. Hope that helps.
(And timing cover leaks are not rare either)
When the internal seal fails on the pump the water leaks out a weep hole under the pump snout. There are also several gaskets involved with the installation of the water pump, also. Get the belt and pulleys off and the problem will likely be obvious.
You can also check the water pump weep holes with an inspection mirror. There should be brown/rusty color streaks or coolant coming out of the holes.
The water pump on your vehicle has a metal cover on the back secured by screws. The gasket for this cover is leaking.
Tester
To learn more, CLEAN the engine front area really good with engine degreaser, brake parts cleaner etc.
Then pressure up the system without running the engine so you can clearly see the first hint of the leak.
A cooling system pressure tester can be rented/loaned at parts places like Auto Zone. It’s a hand air pump with a radiator cap attatchment.
Your water pump sits on TWO gaskets on the front of the timing cover.
water pump - gasket - spacer plate - gasket - timing cover - gasket - block