Jeep CJ 1945-1970 Repair Information

Cooling System



See Figure 1

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Fig. Fig. 1: An antifreeze tester can be used to determine the freezing and boiling level of the coolant

The coolant level should be maintained about 1 / 2 in. (13mm) below the filler neck of the radiator with 4L-134, 4F-134, 6-226 and 6-230 engines.

On the 6-225 engine, the coolant level should be maintained 1 1 / 2 -2 in. (38-51mm) below the bottom of the filler cap when the engine is cold. Since operating temperatures reach as high as 205°F (96°C), coolant could be forced out of the radiator if it is filled too high. The radiator coolant level should be checked regularly, such as every time you refuel the vehicle. Never open the radiator cap of an engine that hasn't had sufficient time to cool or the pressure can blow off the cap and send out a spray of scalding water.

On systems with a coolant recovery tank, maintain the coolant level at the level marks on the recovery bottle.

For best protection against freezing and overheating, maintain an approximate 50% water and 50% ethylene glycol (or other suitable) antifreeze mixture in the cooling system. Do not mix different brands of antifreeze to avoid possible chemical damage to the cooling system.

Avoid using water that is known to have a high alkaline content or is very hard, except in emergency situations. Drain and flush the cooling system as soon as possible after using such water.

Cover the radiator cap with a thick cloth before removing it from a radiator in a vehicle that is hot. Turn the cap counterclockwise slowly until pressure can be heard escaping. Allow all pressure to escape from the radiator before completely removing the radiator cap. It is best to allow the engine to cool if possible, before removing the radiator cap.

Never add cold water to an overheated engine while the engine is not running.

After filling the radiator, run the engine until it reaches normal operating temperature, to make sure that the thermostat has opened and all the air is bled from the system.


See Figures 2, 3 and 4

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Fig. Fig. 2: The cooling system should be pressure tested once a year

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Fig. Fig. 3: Whenever servicing your cooling system, take a few moments to clear the radiator fins of debris, to allow your system to provide maximum engine cooling

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Fig. Fig. 4: Inspect the radiator cap rubber gasket and metal seal for any deterioration at least once a year

When draining coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

To drain the cooling system, allow the engine to cool down BEFORE ATTEMPTING TO REMOVE THE RADIATOR CAP . Then turn the cap until it hisses. Wait until all pressure is off the cap before removing it completely.

To avoid burns and scalding, always handle a warm radiator cap with a heavy rag.

  1. At the dash, set the heater TEMP control lever to the fully HOT position.
  3. With the radiator cap removed, drain the radiator by loosening the petcock at the bottom of the radiator. Locate any drain plugs in the block and remove them. Flush the radiator with water until the fluid runs clear.
  5. Close the petcock and replace the plug(s), then refill the system with a 50/50 mix of ethylene glycol or other suitable antifreeze. Fill the system to 3 / 4 -1 1 / 4 in. (19.05-31.75mm) from the bottom of the filler neck. Reinstall the radiator cap.

If equipped with a fluid reservoir tank, fill it up to the MAX level.

  1. Operate the engine at 2,000 rpm for a few minutes and check the system for signs of leaks.

Radiator Cap Inspection

Allow the engine to cool sufficiently before attempting to remove the radiator cap. Use a rag to cover the cap, then remove by pressing down and turning counterclockwise to the first stop. If any hissing is noted (indicating the release of pressure), wait until the hissing stops completely, then press down again and turn counterclockwise until the cap can be removed.

DO NOT attempt to remove the radiator cap while the engine is hot. Severe personal injury from steam burns can result.

Check the condition of the radiator cap gasket and seal inside of the cap. The radiator cap is designed to seal the cooling system under normal operating conditions which allows the build up of a certain amount of pressure (this pressure rating is stamped or printed on the cap). The pressure in the system raises the boiling point of the coolant to help prevent overheating. If the radiator cap does not seal, the boiling point of the coolant is lowered and overheating will occur. If the cap must be replaced, purchase the new cap according to the pressure rating which is specified for your vehicle.

Prior to installing the radiator cap, inspect and clean the filler neck. If you are reusing the old cap, clean it thoroughly with clear water. After turning the cap on, make sure the arrows align with the overflow hose.