A LITTLE BIT ABOUT RADIATOR CAPS

Your vehicles cooling sytem is pressurized. The coolant operating pressure is regulated by the rating of the radiator cap which contains a relief valve. All radiators are equipped with pressure caps that reduce evaporation of the cooling system and make the engine more efficient by permitting slightly higher operating temperatures. When operating properly, the pressure cap permits pressure to build-up in the cooling system during periods of severe heat load. This pressure increases the boiling point of the coolant and thus reduces overflow losses. When the coolant heats up it expands causing the pressure to build up.

The effectiveness of the radiator cap is limited by its operating pressure and the boiling point of the coolant. All quality radiator caps will have their pressure rating marked on the cap. When a new radiator cap is required , always replace it with a cap of the same type and pressure rating specified. The correct and properly operating radiator cap prevents high pressure coolant from rupturing the radiator, gaskets, seals and hoses.

All Willys vehicles use two basic types of radiatior caps. The MB/GPW/M38/M38A1 and the CJ-2A and some CJ-3A/CJ-5/6 vehicles use a very low pressure cap of just 4 lbs. These radiators have a filler neck with a 2 1/8" inside diameter. All other vehicles use higher pressure caps that are installed on radiators with filler necks with a 1 5/8" inside diameter.

Some MB/GPW and CJ-2A vehicles were equipped with hot climate kits that employ a grille mounted surge tank. This surge tank has a filler neck with a 2 1/8" inside diameter. The Foward Control trucks have a closed cooling system that employs a coolant surge tank. These surge tanks have a filler neck with a 1 5/8" inside diameter.