Antifreeze foaming
 

I have a 1988 F-150 and the other day I was pulling my horse trailer with 2 horses to have them shod. I went about 20 miles. When I arrived I unloaded 1 horse and was standing by the truck when the Antifreeze started to foam out of the overflow hose on the radiator. Any ideas why??? I checked for leaks and found none. It also has no been running hot..

Check your oil to see if it is milky or has bubbles. If so, then you have a leaking head gasket which is allowing the antifreeze to mix with the oil. This is what usually causes the coolant to foam up.

Could you have had too much cooant in the tank? If not then I would keep an eye on it and the temp gauge. You might want to have someone check to see if there is combustion gases in the coolant, which would mean a blown head gasket.

One possibility is that the engine DID become very hot while driving. When you stopped the engine, the water pump stopped circulating coolant and the engine fan was unable to cool the antifreeze then residing in the radiator. The residual heat from the engine caused the cooling system to overpressurize and release pressure and coolant through the hose.

Another possibility is that the transmission became very hot, and the high transmission fluid temperature contributed to the coolant release. The factory transmission cooler runs a line through the radiator.

If you don't have one already, I would consider adding an aftermarket transmission cooler to your truck. Unless those horses are on a diet, you're giving this truck a heck of a workout, particularly in this weather. Excessively hot transmission fluid can change properties and damage a transmission. $$$