Nissan Z - ZX 1970-1988 Repair Guide




See Figures 1 and 2

Exercise extreme care when removing the cap from a hot radiator. Wait a few minutes until the engine has time to cool somewhat, then wrap a thick towel around the radiator cap and slowly turn it counterclockwise to the first stop. Step back and allow the pressure to release from the cooling system. Then, when the steam has stopped venting, press down on the cap, turn it one more stop counterclockwise and remove the cap.

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Fig. Fig. 1: With the engine cool, remove the radiator cap

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Fig. Fig. 2: If needed, add a 50/50 mixture of coolant and water

The manufacturer recommends checking the radiator coolant every time you stop for gas. Dealing with the cooling system can be a dangerous matter unless the proper precautions are observed. It is best to check the coolant level in the radiator when the engine is cold. This is done by removing the radiator cap and seeing that the coolant is within 2 in. (51mm) of the bottom of the filler neck.

On 1976 and later models, the cooling system is equipped with an expansion tank. If coolant is visible above the MIN mark on the tank, the level is satisfactory. Always be certain that the filler caps on both the radiator and the reservoir are tightly closed.

In the event that the coolant level must be checked when the engine is warm on a vehicle without the expansion tank, place a thick rag over the radiator cap and slowly turn the cap counterclockwise until it reaches the first detent. Allow all of the 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 low, add equal amounts of antifreeze and clean water. On models without an expansion tank, add coolant through the radiator filler neck. Fill the expansion tank to the MAX level on vehicles with that system.

Never add cold coolant to a hot engine unless the engine is running, to avoid cracking the engine block.

The radiator hoses, clamps and the radiator cap should be checked at the same time as the coolant level. Hoses which are brittle, cracked or swollen should be replaced. Clamps should be checked for tightness (screwdriver tight only-DO NOT allow the clamp to cut into the hose or crush the fitting). The radiator cap gasket should be checked for any obvious tears, cracks, swelling or any signs of incorrect seating in the radiator neck.


See Figures 3, 4, 5 and 6

When draining the coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze, and could 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.

Once every 24 months or 24,000 miles (38,000 km), the cooling system should be drained, thoroughly flushed and refilled. This should be done with the engine cold.

Completely draining and refilling the cooling system at least every two years will remove accumulated rust, scale and other deposits.

Use a good quality antifreeze with water pump lubricants, rust inhibitors and other corrosion inhibitors along with acid neutralizers. Use a permanent type coolant that meets the manufacturer's specifications found in your owner's handbook.

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Fig. Fig. 3: To drain the coolant from the radiator, loosen the draincock at the bottom of the radiator

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Fig. Fig. 4: The engine block drain plug is found at the left rear of the block-1970-73 models

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Fig. Fig. 5: For 1984-85 models, the drain plug is located on the right side of the engine

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Fig. Fig. 6: 1986 and later models have the drain plug on the left side of the engine block

  1. Remove the radiator cap.
  3. There are two drain plugs in the cooling system: one at the bottom of the radiator and one at the rear of the driver's side of the engine. Both should be loosened to allow the coolant to drain.
  5. Turn on the heater control to its hottest position. This ensures that the heater core is flushed out completely. Flush the system thoroughly by refilling it with clean water; flush it through the radiator opening as it escapes from the two draincocks. Continue until the water running out is clear. Be sure to clean out the coolant recovery tank as well, if equipped.
  7. If the system is badly contaminated with rust or scale, use a commercial flushing solution to clear it; follow the manufacturer's instructions. Some causes of rust are air in the system, caused by a leaky radiator cap or an insufficiently filled or leaking system; failure to change the coolant regularly; use of excessively hard or soft water and failure to use a proper mix of antifreeze and water.
  9. When the system is clear, allow all the water to drain, then close the drain plugs. Fill the system, through the radiator neck, with a 50/50 mix of antifreeze and water.
  11. Start the engine and top off the radiator with the antifreeze and water mixture. If equipped with a coolant recovery tank, fill it half full with the coolant mix.
  13. Replace the radiator and coolant tank caps, then check for leaks. When the engine has reached normal operating temperatures, shut it off, allow it to cool, then top off the radiator or coolant tank as necessary.


See Figure 7

Most permanent antifreeze/coolant products have a colored dye added which makes the solution an excellent leak detector. When servicing the cooling system, check for leakage at:

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Fig. Fig. 7: With a pressure tester, coolant leaks can be found more easily

All hoses and hose connections

Radiator seams, radiator core, and radiator draincock

All engine block and cylinder head freeze (core) plugs, and drain plugs

Edges of all cooling system gaskets (head gaskets, thermostat gasket)

Transmission fluid cooler

Heating system components and water pump

Check the engine oil dipstick for signs of coolant in the engine oil. Also check the coolant in the radiator for signs of oil in the coolant. Investigate and correct any indication of coolant leakage.

Check the Radiator Cap

See Figure 8

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.

A worn cap should be replaced with a new one.

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Fig. Fig. 8: Check the condition of the rubber seal and gasket on the cap

Clean Radiator of Debris

See Figure 9

Periodically clean any debris such as 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 needlenose 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.

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Fig. Fig. 9: Remove any debris from the radiator fins


See Figure 10

A 50/50 mix of coolant concentrate and water will usually provide protection to -35°F (-37°C). Freeze protection may be checked by using a cooling system hydrometer. Inexpensive hydrometers (floating ball types) may be obtained from a local department store (automotive section) or an auto supply store. Follow the directions packaged with the coolant hydrometer when checking protection.

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Fig. Fig. 10: An inexpensive float-type tester can be used to check the coolant protection level