While antifreezing compounds can be used in the cooling systems of automobiles, they are not suitable for tractors because the greater and more continuous heat quickly evaporates them. The danger of freezing is very great, and must be avoided; the water in the radiator and jackets is in thin sheets, and will freeze when a bucket of water standing in the open will not show any signs of ice. The only real protection against freezing is to drain out all the water whenever the tractor is to stand idle for a sufficient time for it to cool off. Petcocks are provided for this at the lowest points of the system, and also in the pump when forced circulation is used. The freezing of even a small pocket of water will be enough to crack a cast-iron water jacket wall, and the best assurance that the system is thoroughly drained is to open the drain cocks while the engine is still running, shutting down as the flow stops. When putting up a tractor for the winter it should be thoroughly protected from rust and corrosion. The last time that the tanks are filled a quart of light oil should be added for every five gallons of gasoline or kerosene; as the tank empties this will leave a coating of oil on the inside walls. Fuel tanks and water system should be drained, and particular care should be taken that all the water is out; the drain cocks should be left open. A mechanical oiler should be filled full, to protect the steel parts of the pumps from rust. A half pint of thick oil should be put into each cylinder, and spread to the cylinder and piston walls by cranking for a few turns. Oil should be run between the valves and their seats. All exterior parts should be protected by a coat of thick oil or by paint. The governor rod, push rods, and similar parts should be especially looked after. It is advisable to take off the magneto and store it in a safe, dry place; spark plugs should be left in position. The tractor should be covered with a tarpaulin and stored in a tight shed. When going over a tractor preparatory to laying it up, a list should be made of all parts that need renewal. These parts should be procured at once; they are more readily obtained during the winter than in the operating season, and will be on hand for the spring overhaul. CHAPTER XII ENGINE MAINTENANCE FUEL SYSTEM AND CARBURETOR The operation of a carburetor depends on so many things that no exact instructions for its adjustment can be given. The best that can be done is to give a general idea of the requirements, and to outline a plan by which the adjustment can be arrived at. The many makes and designs of carburetors and vaporizers that are used on tractors have different kinds of adjustments; on most of them the only adjustment is the needle valve that controls the fuel, but some also have adjustable air valves. In any case, the manufacturer’s instruction book should be studied for the understanding of the particular carburetor in question.