Guys!!! you should be able to start the tractor cold,,, and let it idle with no radiator cap on... It SHOULD not blow out coolant. Removing a cap from a hot tractor can be hazardous, but cold????
And as it idles, you look for bubbles coming out the radiator, normally a sign of a slight head gasket leak... In the case of water being blown out,,, its a fully blown gasket, or big crack in the head... where ALL of the compression is getting blown into the water jacket, and then out the radiator. A fully blown gasket puts up to 120 lbs into the water jacket, and the cap is only 6 or 7 lbs on a stock ford cap, changed to 12 lbs on later models..
SO... if its blowing cold,,, run a compression check to see if one cyl is low,,, or two adjacent cyls are low so you know where to look for cracks when you pull the head off. Hopefully its just a failed gasket and not a cracked block from freezing, or a cracked head from overheating. replacing a cap when it blowing water out is a waste of time and money. And if he got a generic cap, it will be 13 lbs instead of the original 6 lb cap on the 3000...iirc.
Either way.. good luck and let us know what you find.