78 400M overheating

ok, this truck has been my daily driver for 9 years now and i haven't had to do any major work to the engine, but i think it overdue. my problem is it continues to overheat, and is losing coolant rapidly. New thermostat, radiator (2 years old), radiator cap, hoses, and heater core. I can put 3 gallons of coolant in and after driving about 100 miles she is almost bone dry. i am losing some out of overflow after she gets hot which is understandable. Of course after i fill it up it runs normal until it starts to burn/leak the coolant out again. Another thing i am on my fifth water pump within the last 7 years. what's the deal with this. coincidence or something else. Im thinking head gasket, and was wandering the tell tale signs of this. Also If its hot outside it will pop out of the exhaust while driving 55-60 mph, but not constant, just mainly when under load. My dad seems to think i have a hole in one of my pistons, he said he had similiar problems in a 351. never found out what it was until after installing new motor and looking over the old. thanks for any and all suggestions.

Well tell tail sings of a bad head gasket are one or both of the following.

1. White smoke emitted from your exhaust. It will also have a sweet odor to it if you are running any antifreeze.
2. White frothy looking oil.

You will also see water in you oil if you change it after it has set overnight.
I would say that if you are losing 3 gallons in 100 mile that you should see one of these two things happening.

my oil looks fine, but i do get the white smoke only when i first start it after it has sat for a day or two. this is really driving me nuts. yes, the exhaust smells, but not really sweet like coolant just horrible. makes you almost gag. it prolly is the head gasket, just want to make sure before i start tearing it apart. any suggestions on why i keep going through water pumps? Is it just because it keeps getting hot and "burns" them up or what

It could ba a head gasket, or several other things. Could be a cracked head from one of the previous run hot episodes. Sometimes theyll crack in an intake or exhaust port runner, the hotter it gets, the bigger the crack, the more water u lose. Check the spark plugs, if its on the intake side, one or more of the plugs will be cleaner than the rest. A pressure test will let u hear it in the exhaust sometimes, Also, on fords of this era they sometimes had an aluminum spacer under the carb that water was circulated through from a heater hose. Ive seen these corrode, and get pinholes allowing water to get into the intake. As far as the water pump, the cooling system could have alot of rust , and need flushing. Waterpumps have a rotating element inner seal that can be damaged by rust, and other debris in the system. Also, overtightning the belts can put excessive side load on pump bearings, and cause premature failure. Before you go tearing it down, maybe flush it with cleaner. There are several available, and one is about as good as the other anymore. Theyve taken most of the good stuff off the market. I use vinegar on ones that are really bad. Put it in and drive it a few days, take the thermostat out and flush it out good. Once you get it as clean as you can, put a large bottle of "Bars Leaks" in it. It works great, will seal some pretty good size leaks, and is compatible with antifreeze. About the only leak it wont work for , is if youre leaking compression into the cooling system, which it doesnt sound like you are. Good luck.
Later
Ed

i have flushed it before, but i will try again using your suggestion with the vinegar. Yes i do have that spacer under the carb, always wandered what it was for so i will check that out also. that is about the only thing i haven't really looked into yet. Cracked head, man i hope not, but after talking with some people at work they said the 400M had trouble with this. Ive had a lot of run hot episodes over the last two years, and i mean a lot, so i guess i wouldn't be suprised. I will check the spark plugs and the spacer as mentioned. So should i be getting water in my oil if it was a cracked head or bad head gasket, because im not seeing any sign. i'll drain it again tomorrow and put new in, then check it again but im not seeing any sign of water in the oil. i'll keep you posted. thanks so much for your reply and hopefully i'll get this figured out.

A cracked head or leaking headgasket either one can cause water to get into the oil, depending on where the damage is. But it doesnt always happen, and if it were, you would see it right away, as someone else said, it would look like muddy milk.

Ps: also check real good for external leaks like : waterpump, pinhole in a hose or thermostat housing, radiator, heater core...ect. if u can borrow or rent a pressure tester, pressure the system up to 20-25 # with it full of water, and look for leaks. check the radiator cap and coolant recovery reservoir. losing that much water, if it is going through the engine, u should be seeing vapor in the exhaust.