Ok, the 400 in my truck is now doing something else to make me worry. It is using water. I dont know if it is burning it off or what. There is no smoke at all and no leaks. I am down to straight water in it because i gave up on refilling with antifreeze. Any ideas on how much time this old truck has left in her?

 

Engine running hot or losing coolant out the overflow line on radiator?See any compression bubbles or signs of in the coolant?Check each spark plug and see if there is any signs or no carbon or color on tip and insulator.Water/antifreeze makes a great carbon remover.Usually the cylinder that is burning the coolant will look almost new.Let us know what you find.

 

Engine stays cool until it runs low on water, I will have to pull the plugs sometime this week, heat index is up to 112 tomorrow so it wont be then. No external signs of puking out of the overflow either. No sign of it in the oil either.

 

Well not having that antifreeze in there still will cause it to overheat, as antifreeze dissipates heat better than straight water and raises boil over temp.

 

could be as simple as bad radiator cap, they don't last forever and sometimes don't show signs of leaking. like Maskedman says, i always look at the plugs.