I have a 94 F150 with the 5.8 V8 that I rarely drive. I've been having problems holding coolant for quite awhile. I replaced the water pump about a year ago and that seemed to help some but now everytime I drive it (about once a month) I need to add coolant.

I can't find any leaks but it's bone dry. Anybody have any ideas? I'm pretty lost.

 

Have you checked the oil? Is it milky white?
Do you smell coolant?
What about the tailpipe(s), is there any coolant there?

Also, check the drivers side freeze plugs and oil pan for leaks. Also check the y-pipe just aft of the crossmember. Are there any white streak marks/coolant trails?