Ford Mustang/Capri 1979-1988 Repair Guide

Cooling System



The proper coolant for your vehicle is a 50/50 mix of an ethylene glycol-base antifreeze/coolant and water. Ethylene glycol-base antifreeze/coolant contains water pump lubricants, rust inhibitors and other corrosion inhibitors, as well as acid neutralizers. Alcohol or methanol base coolants are not recommended. Antifreeze solutions should be used, even in summer, to prevent rust and to take advantage of the solution's higher boiling point compared to plain water. This is imperative on air conditioned vehicles; the heater core can freeze if it is not protected.


See Figures 1, 2 and 3

Exercise extreme care when removing the cap from a hot radiator. Wait a few minutes until the engine has time to cool, 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.

The coolant level in the radiator should be checked on a monthly basis, when the engine is cold. On a cold engine, the coolant level should be maintained at one inch below the filler neck on downflow radiators, and 2 1 / 2 in. below the filler neck at the "COLD FILL'' mark on crossflow radiators. On cars equipped with the Coolant Recovery System, the radiator is normally full when the level is maintained at the "COLD LEVEL'' mark in the translucent plastic expansion bottle. Top off as necessary with a mixture of 50% water and 50% ethylene glycol antifreeze, to ensure proper rust, freezing and boiling protection. If you have to add coolant more often than once a month or if you have to add more than one quart at a time, check the cooling system for leaks. Small amounts of coolant often escape at loose hose fittings or failing water pumps, and are evidenced by a white telltale residue.

The presence of coolant in the crankcase oil suggests a more serious problem, such as a blown cylinder head gasket. If this situation exists, it is recommended that the engine not be operated until the problem has been identified and repaired. In so doing, engine damage should be kept to a minimum.

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Fig. Fig. 1: Carefully remove the radiator cap, preferably when the engine is cool

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Fig. Fig. 2: Fill level - downflow and crossflow radiators

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Fig. Fig. 3: Coolant recovery system variations


See Figures 4, 5, 6, 7 and 8

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.

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

  1. Drain the existing coolant/water mixture. Open the radiator and engine drain petcocks (on models so equipped), or disconnect the bottom radiator hose, at the radiator outlet. Set the heater temperature controls to the full HOT position.

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

  1. Close the petcock(s) or reconnect the lower hose and fill the system with water.
  3. Add a can of quality radiator flush. Be sure the flush is safe to use in engines having aluminum components.
  5. Idle the engine until the upper radiator hose gets hot.
  7. Drain the system again.
  9. Repeat steps 2, 4 and 5 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. It may be helpful to remove the reservoir before flushing, so that old coolant and water can be poured out.
  15. If applicable, reinstall the coolant recovery system reservoir.
  17. Determine the capacity of your cooling system. Refer to the Capacities Specifications chart in this section for details. Add a 50/50 mix of quality antifreeze/coolant and water to provide the desired protection. If equipped with a coolant recovery system, be sure to fill the reservoir to the indicated level after filling the radiator.

Since a fair amount of water will remain in the system after draining, especially on engines without drain petcocks, it is a good practice to add the full allotment of undiluted antifreeze/coolant before topping off with water. This will avoid the annoying problem of insufficient room for the recommended amount of coolant. When pouring in the unmixed coolant, be sure to limit the quantity to one-half of the total cooling system capacity.

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Fig. Fig. 4: Opening the radiator drain petcock

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Fig. Fig. 5: Carefully lift off the cap from the coolant recovery system reservoir

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Fig. Fig. 6: The coolant recovery system reservoir is retained by bolts

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Fig. Fig. 7: Removing the coolant recovery system reservoir

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Fig. Fig. 8: Adding coolant to the coolant recovery system reservoir


In addition to the chemical flush mentioned above, a good way to eliminate or prevent the build-up of unwanted deposits is to reverse flush the entire cooling system with high pressure water. Inexpensive kits which can be permanently installed for this purpose are available at auto parts stores. If you prefer to reverse flush your vehicle's cooling system without using such a kit, proceed as follows:

  1. Drain the cooling system.
  3. Close the petcock or reconnect the lower radiator hose.
  5. Remove the thermostat from the engine. Disconnect the upper radiator hose at the radiator neck.
  7. Install a high pressure hose into the thermostat housing and allow the water pressure to reverse flush the system.
  9. Continue this procedure until the water coming from the hose is clean.
  11. Reconnect the upper radiator hose and reinstall the thermostat with a new gasket and water-resistant sealer.
  13. Refill the cooling system with a mixture of fresh coolant and water.


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

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, water pump
Check the engine oil dipstick for signs of coolant in the engine oil
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 9

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. 9: Check the radiator cap gasket for cracks or wear

Clean Radiator of Debris

See Figure 10

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Fig. Fig. 10: Clean debris from the radiator fins

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 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.


See Figure 11

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 auto supply store. Follow the directions packaged with the coolant hydrometer when checking protection.

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Fig. Fig. 11: Testing coolant protection with a hydrometer