Mazda Trucks 1972-1986 Repair Guide

Cooling System


See Figures 1, 2, 3, 4 and 5

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Fig. Fig. 1: Check antifreeze protection level with an inexpensive tester

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

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Fig. Fig. 3: Cooling systems should be pressure tested for leaks periodically

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Fig. Fig. 4: Check coolant level at the coolant reservoirit should be at or above the FULL mark with the engine at normal operating temperatureif low, remove the cap ...

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Fig. Fig. 5: ... and add coolant as necessarya 50/50 mix of antifreeze/water should be used

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.

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.


See Figure 6

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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.


See Figure 7

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

Periodically clean any debrisleaves, 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 carefulthe fins are very soft. Don't wiggle the fins back and forth too much. Straighten them once and try not to move them again.


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

  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.

Before opening the radiator petcock, spray it with some penetrating lubricant.

  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.