On a dozer, normal direction on the fan pushes air through the radiator like yours is doing, so no problem there.
As far as the issue of water being forced from under the radiator cap I ask this. Is the water actually coming from under the screw on cap, or from under the pressure relief valve that sits on top of the tank, near the cap? The way CAT does the older equipment the actual screw on cap should seal, and not leak at all, unless the seal is shot. Instead they have a pressure regulating valve on the top of the tank to relieve any excess pressure. So,typically, if the cap is leaking then the seal on it is worn completely out, or worn such that it is letting the coolant past at it a lower pressure than the actual relief. This, in turn, usually happens because the relief is stuck from getting packed with dust and dirt over the years. There are either 4 or 5 bolts (been awhile) that hold the assembly to the tank. Carefully pull those bolts (they tend to be rusty and will twist off easily if your not careful) and you should be able to take everything apart and clean it up. You might find the actual valve seal is shot and you'll need another, but often you'll get lucky and be able to reuse the old one. Either way clean it up and reassemble it in the same order it all came apart. Once together it should relieve pressure on the radiator, instead of the cap seal doing it, unless the seal on the cap is shot as I said earlier.
Beyond that, if you are topping the tank completely off, most systems will spit out some coolant and 'seek their own level', regardless to any of what I said above. In other words what is happening may also be perfectly normal as long as it's happing through the relief and not the cap.
Hope this helps.