Ford Mustang/Cougar 1964-1973 Repair Guide

Cooling System


See Figures 1 and 2

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Fig. Fig. 1: Remove the cap and look in the radiator to check the fluid level

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Fig. Fig. 2: Top off the fluid with the correct amount of anti-freeze and water mixture


The coolant level in the radiator should be checked at least once a month. On a vertical-flow radiator, the level of the coolant must be 1 inch below the radiator cap seat. The cross-flow radiator is at proper level when the coolant level is 2 inch below the cap seat at the cold fill mark. Both types of radiator should only be checked when the engine is cold and not running. If it is imperative that the level of a hot engine must be checked, muffle the radiator cap with a thick cloth and turn it slowly counterclockwise until the pressure starts to escape. After the pressure has completely dissipated, finish removing the cap. Some 1972 and later vehicles are equipped with a constant full coolant recovery system. On these models there is a plastic recovery tank adjacent to the radiator. When adding coolant to a constant full system, add only to the plastic tank and not to the radiator.

When adding coolant between changes, use a mixture of permanent antifreeze and water that keeps the freeze protection at an adequate level for the temperatures that may occur in the area. A minimum freeze protection level should be maintained to at least 0°F to prevent boiling and corrosion. Do not mix brands or types of antifreeze.


Radiator and Hose

See Figures 3, 4, 5 and 6

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Fig. Fig. 3: Be sure the rubber gasket on the radiator cap has a tight seal

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Fig. Fig. 4: Periodically remove all debris from the radiator fins

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Fig. Fig. 5: Cooling systems should be pressure tested for leaks periodically

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Fig. Fig. 6: Cutaway view of a typical cooling system flow

If coolant level is constantly low, there is a possibility that the cooling system is leaking. Check the radiator core and tanks for seepage at the seams. Inspect all radiator and heater hoses for evidence of heat cracking or leaking. Replace any hose in questionable condition. Check for proper installation of hoses in supporting brackets. Make sure there are no bends or kinks in hoses at fittings.


Ford recommends that the coolant be drained, flushed, and replaced every two years or 24,000 miles. To drain the system, open the drain cock at the bottom of the radiator and remove the cylinder block drain plugs. On six-cylinder models, the drain plug is located at the right rear of the block near the starter. On V8 models, there are two drain plugs, one on each side of the block.

To remove rust, sludge, and other foreign material from the cooling system, a cooling system cleanser should be used. In severe cases of rust or sludge deposits, it will be necessary to use the pressure flushing method. A reversed-direction water flow will loosen sediment more quickly than a steady flow in the normal direction of coolant flow. Before pressurizing the system, make sure that the cylinder head bolts are tightened to specifications to prevent possible water leakage into the cylinders.

Always remove the thermostat prior to pressure-flushing.

To fill the cooling system, close the radiator drain cock. Install the cylinder block drain plugs. Disconnect the heater outlet hose at the water pump to release trapped air in the system. When the coolant begins to escape, connect the hose. After operating the vehicle at 2,000 revolutions per minute (rpm) for approximately 20 minutes, the level of coolant may drop, due to the displacement of entrapped air in the system. Refill to proper level.

The antifreeze used should be of the ethylene glycol, permanent type. Mixture strength must provide minimum protection to 0°F. To avoid possible overheating in hot weather, do not use mixtures with more than 50 percent antifreeze except in areas anticipating -35°F temperatures. When running a minimum solution of antifreeze to water, it is good practice to add rust inhibitor to the cooling system.

The hose connecting the heater valve to the intake manifold must be replaced each time the coolant is replaced.