> I went to town today (90 miles round trip) & bought a new radiator cap. Now the tractor wonít start. Put battery on charger & will try again tomorrow.
It is not the radiator cap. Best case scenario is it's the head gasket, which is not particularly expensive or difficult to replace. Worst case you have a cracked head, but you won't know until you pull the head to replace the head gasket.
This site sells the head gasket alone for 20 dollars or with the valve cover and manifold gaskets for 42 bucks. Your local New Holland dealer probably has them in stock as well.