Mitsubishi Pick-ups and Montero 1983-1995 Repair Guide

Cooling System


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.


Propylene glycol and ethylene glycol antifreeze are not compatible and must not be mixed together. Refer to the label on antifreeze/ coolant container if necessary.

Mitsubishi recommends the use of a quality ethylene glycol coolant containing corrosion inhibitors, and approved for use with all the metals in the engine, including aluminum. Mitsubishi recommends against the use of additional cooling system additives as they may be incompatible with the coolant itself.


See Figures 1, 2, 3 and 4

Coolant level should always be checked by simply looking at the level in the overflow tank. If there is a coolant leak, the level in the tank will drop as the coolant is drawn back into the radiator. If there is no coolant visible in the tank, the coolant level needs to be checked by removing the radiator cap. Also, if there are indications that the engine is overheating, it is wise to check the level in the radiator, as a defective cap may permit the level to drop there even though there is an ample supply in the overflow system.

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Fig. Fig. 1: Simply check the overflow system level by comparing the fluid level with the FULL and LOW level indicators on the overflow container

One of the reasons for the use of an overflow system is that it is often hazardous to remove the radiator cap. Under normal operating conditions, the temperature of the engine block exceeds the boiling point of the coolant. The pressure cap increases pressure in the cooling system, thereby increasing the boiling point of the fluid in the system. Thus, removing the cap on an engine that is still near operating temperature will usually result in a discharge of boiling hot coolant. The situation worsens substantially if the cooling system is dirty or the engine is overheating.

Thus the first rule to remember is: NEVER REMOVE THE RADIATOR CAP UNTIL THE ENGINE HAS COOLED SUBSTANTIALLY BELOW OPERATING TEMPERATURE. Then, unless the engine is dead cold, USE A HEAVY RAG TO COVER THE CAP. Finally, TURN THE CAP SLOWLY TO THE FIRST NOTCH. This will release the system pressure. Give the pressure time to drop, and then remove the cap. If the radiator cap is badly worn, the pressure may not be released. This is why it is necessary to use the rag, cool the engine first, and still proceed cautiously and slowly.

Once the cap has been removed, you can add a 50-50 mix of antifreeze and water slowly to the radiator until the level increases. Once the level is near the top of the radiator tank, start the engine. Let the engine idle until the thermostat opens (you'll see coolant flow through the top of the radiator tank and the upper radiator hose will become hot). Air in the system will be expelled at this point, causing the level of coolant to drop again. Keep adding coolant until the level remains near the top of the radiator. Then, install the cap, add coolant to the overflow tank until it is well past the lower mark and install the overflow tank cap as well.

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Fig. Fig. 2: Once the engine has cooled down and the pressure in the system is relieved, remove the radiator cap

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Fig. Fig. 3: With the radiator cap removed, fill the system with a 50-50 mixture of water and antifreeze

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Fig. Fig. 4: Once the system is completely filled, fill the overflow reservoir to the FULL mark


See Figure 5

It's best to drain the cooling system when the engine is warm (but has cooled to well below operating temperature for safety) to assist in complete removal of old coolant and any suspended material. Follow the procedure below to help ensure you will not be burned by hot coolant.

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Fig. Fig. 5: Cooling system air bleed bolt location-6-cylinder engines

  1. Loosen the drain cock or remove the drain plug located on the bottom of the radiator tank. This will begin the draining process and relieve pressure. DON'T START OUT BY REMOVING THE CAP! Just make sure you are well away from the direction the coolant flow will take when you remove the plug, and then remove it.

Draining hot water can cause painful burns. Be careful when doing this.

  1. Once coolant flow out of the bottom of the radiator has slowed, remove the radiator cap to vent the system. Then, remove the coolant drain plug from the side of the engine block.
  3. When all the coolant has drained, replace the plugs. If the hoses need attention, this is an ideal time to replace them. Slowly fill the system with water until the water level reaches the top of the radiator tank. Start the engine and run it at idle. When the thermostat opens and water begins to flow through the top of the radiator, add more water as necessary until the engine is full. Shut the engine OFF and again carefully remove both drain plugs. Repeat the process of filling the system with water and draining it until drained water is clear.

If the system cannot be cleaned out effectively this way, you may want to buy a reverse flushing kit at your local parts store and use it. An alternative is the use of a chemical cleaner; if you need to use one of these, just make sure it is compatible with the use of aluminum engine parts and that you follow the directions on the can carefully to ensure that you do not damage your engine.

  1. Coat both drain plugs with sealer and install them snugly. Look up the coolant capacity in the Capacities Chart, later in this section. See the chart on the side of the antifreeze container in order to calculate just how much antifreeze is required to protect the system down to the lowest expected temperature in your area. Pour the antifreeze in first. Then, follow up with clean water until the level reaches the top of the radiator tank. You can also pre-mix the antifreeze and water before filling the system. Finally, follow the steps at the end of the preceding procedure for filling the system with coolant after checking the level.

If equipped, always open the air relief plug or bolt before filling the cooling system. This service procedure is for bleeding the trapped air in the cooling system. Only when the cooling system is bled properly can the correct amount of coolant be added to the system. The 3.0L (24 valve) and 3.5L engines have a caution label near the air bleed bolt or plug.