Chevrolet Full-size Cars 1968-1978 Repair Guide

Cooling System


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Fig. Fig. 1 Cooling systems should be pressure tested for leaks periodically

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Fig. Fig. 2 Cutaway view of a typical cooling system flow

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Fig. Fig. 3 Coolant protection can be checked with a simple float-type tester

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Fig. Fig. 4 Coolant recovery, closed system pressure cap

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Fig. Fig. 5 The coolant recovery tank is mounted on the right fender skirt

Never remove the radiator cap under any conditions while the engine is running! Failure to follow these instructions could result in damage to the cooling system or engine and/or personal injury. To avoid having scalding hot coolant or steam blow out of the radiator, use extreme care when removing the radiator cap from a hot radiator. Wait until the engine has cooled, then wrap a thick cloth around the radiator cap and turn it slowly to the first stop. Step back while the pressure is released from the cooling system. When you are sure the pressure has been released, press down on the radiator cap (still have the cloth in position) turn and remove the radiator cap.

Dealing with the cooling system can be dangerous matter unless the proper precautions are observed. It is best to check the coolant level in the radiator when the engine is cold. On early cars this is accomplished by carefully removing the radiator cap and checking that the coolant is within 22 inches of the bottom of the filler neck. On later cars, the cooling system has, as one of its components, a coolant recovery tank. If the coolant level is at or near the FULL COLD line (engine cold) or the FULL HOT line (engine hot), the level is satisfactory. Always be certain that the filler caps on both the radiator and the recovery tank are closed tightly.

In the event that the coolant level must be checked when the engine is hot on engines without a coolant recovery tank, place a thick rag over the radiator cap and slowly turn the cap counterclockwise until it reaches the first detent. Allow all hot steam to escape. This will allow the pressure in the system to drop gradually, preventing an explosion of hot coolant. When the hissing noise stops, remove the cap the rest of the way.

If the coolant level is found to be low, add a 50/50 mixture of ethylene glycol-based antifreeze and clean water. On older cars, coolant must be added through the radiator filler neck. On newer cars with the recovery tank, coolant may be added either through the filler neck on the radiator or directly into the recovery tank.

Never add coolant to a hot engine unless it is running. If it is not running you run the risk of cracking the engine block.

If the coolant level is chronically low or rusty, refer to Cooling System Troubleshooting Chart at the end of this section.

At least once every 2 years, the engine cooling system should be inspected, flushed, and refilled with fresh coolant. If the coolant is left in the system too long, it loses its ability to prevent rust and corrosion. If the coolant has too much water, it won't protect against freezing.

The pressure cap should be looked at for signs of age or deterioration. Fan belt and other drive belts should be inspected and adjusted to the proper tension. (See checking belt tension).

Hose clamps should be tightened, and soft or cracked hoses replaced. Damp spots, or accumulations of rust or dye near hoses, water pump or other areas, indicate possible leakage, which must be corrected before filling the system with fresh coolant.


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Fig. Fig. 6 Be sure the rubber gasket on the radiator cap has a tight seal

While you are checking the coolant level, check the radiator cap for a worn or cracked gasket. If the cap doesn't seal properly, fluid will be lost and the engine will overheat.

Worn caps should be replaced with a new one.


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Fig. Fig. 7 Periodically remove all debris from the radiator fins

Periodically clean any debris-leaves, paper, insects, etc.-from the radiator fins. Pick the large pieces off by hand. The smaller pieces can be washed away with water pressure from a hose.

Carefully straighten any bent radiator fins with a pair of needle nose pliers. Be careful-the fins are very soft. Don't wiggle the fins back and forth too much. Straighten them once and try not to move them again.


When adding or changing the fluid in the system, create a 50/50 mixture of high quality ethylene glycol antifreeze and water.


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Fig. Fig. 8 If coolant is to be added to the coolant recovery tank, simply twist off the cap ...

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Fig. Fig. 9 ... then, using a funnel, add a 50/50 mixture of coolant/water to bring the fluid up to the FULL mark

The fluid level may be checked by observing the fluid level marks of the recovery tank. The level should be below the ADD mark when the system is cold. At normal operating temperatures, the level should be between the ADD and the FULL marks. Only add coolant to bring the level to the FULL mark.

Should it be necessary to remove the radiator cap, make sure that the system has had time to cool, reducing the internal pressure.


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Fig. Fig. 10 To drain the radiator, loosen the petcock located below the lower radiator hose

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Fig. Fig. 11 As the coolant starts to drain, remove the radiator cap

Completely draining and refilling the cooling system every two years at least will remove accumulated rust, scale and other deposits. Coolant in late model cars is a 50/50 mixture of ethylene glycol and water for year round use. Use a good quality antifreeze with water pump lubricants, rust inhibitors and other corrosion inhibitors along with acid neutralizers.

The cooling system should be drained, thoroughly flushed and refilled at least every 30,000 miles or 24 months. These operations should be done with the engine cold.

  1. Drain the existing antifreeze and coolant. Open the radiator and engine drain petcocks, or disconnect the bottom radiator hose, at the radiator outlet.

When draining the coolant, keep in mind that cats and dogs are attracted by the 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.

  1. Close the petcock or reconnect the lower hose and fill the system with water.
  3. Add a can of quality radiator flush.
  5. Idle the engine until the upper radiator hose gets hot.
  7. Drain the system again.
  9. Repeat this process until the drained water is clear and free of scale.
  11. Close all petcocks and connect all the hoses.
  13. If equipped with a coolant recovery system, flush the reservoir with water and leave empty.
  15. Determine the capacity of your coolant system (see capacities specifications). Add a 50/50 mix of quality antifreeze (ethylene glycol) and water to provide the desired protection.
  17. Run the engine to operating temperature.
  19. Stop the engine and check the coolant level.
  21. Check the level of protection with an antifreeze tester, replace the cap and check for leaks.