Ford Pick-ups and Broncos 1987-1996 Repair Guide

Cooling System



Completely draining and refilling the cooling system every two years at least 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.

Additionally, whenever servicing the cooling system, 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 1

Click image to see an enlarged view

Fig. Fig. 1: Check the radiator cap gasket for cracks or wear

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.

  1. Allow the engine to cool and remove the radiator cap. Because a coolant recovery (overflow) tank is used, the coolant level should be at the cap seal in the filler neck. The coolant should be clear green or clear blue in color (depending on the brand of coolant used).
  3. Examine the fluid color:

    If the coolant is a very light green or blue, there is less than a 50/50 mixture and the system should be drained and refilled.
    If the coolant is muddy brown in color, it is likely that an unapproved stop-leak has caused the discoloration. This may eventually plug the system and cause overheating. The best course of action would be to empty the system, repair the leak and refill with the correct 50/50 mixture of ethylene glycol and water.
    If the coolant is reddish brown, there is rust in the system. The entire cooling system should be flushed and refilled.
    If there is an iridescent sheen floating on top of the coolant, there is likely a small amount of engine oil leaking into the system. Check the oil dipstick to look for drops of greenish coolant or whether the oil is milky in appearance. If the oil checks out normal, the sheen on top of the coolant may not be an immediate problem, but be advised it may grow worse and should be closely monitored during routine maintenance.
    If the coolant is milky brown (like coffee with heavy cream) engine oil is entering the cooling system. On 7.3L diesel and 7.5L gasoline engines, the oil cooler is the most likely cause of the problem and should be checked first. Next check in order: the head gasket, cylinder block and cylinder head. Check also the transmission for traces of coolant (the transmission fluid will be milky). If found, the transmission should be flushed and refilled.


  1. Assuming the coolant is normal, add fluid as necessary.

While you are checking the coolant level, check the radiator cap for a worn or cracked gasket. It the cap doesn't seal properly, fluid will be lost and the engine will overheat. Worn caps should be replaced with a new one of the same presure rating.


See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: Keep the radiator fins clear of debris for maximum cooling

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.


See Figures 3, 4, 5, 6, 7, 8 and 9

Click image to see an enlarged view

Fig. Fig. 3: Location of the radiator draincock-F-150 shown

Click image to see an enlarged view

Fig. Fig. 4: Check antifreeze protection with an inexpensive tester

Click image to see an enlarged view

Fig. Fig. 5: Coolant level check

Click image to see an enlarged view

Fig. Fig. 6: Open the radiator petcock to drain the cooling system. Spray first with penetrating oil

Click image to see an enlarged view

Fig. Fig. 7: The system should be pressure tested once a year

Click image to see an enlarged view

Fig. Fig. 8: Coolant recovery system

Click image to see an enlarged view

Fig. Fig. 9: Fill the cooling system with the correct mixture and amount of coolant

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

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

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. Place the heater control in the HOT position.
  7. Idle the engine until the upper radiator hose gets hot.
  9. Drain the system again.
  11. Repeat this process until the drained water is clear and free of scale.
  13. Close all petcocks and connect all the hoses.
  15. If equipped with a coolant recovery system, flush the reservoir with water and leave empty.
  17. Determine the capacity of your coolant system (see the Capacities specification chart). Add a 50/50 mix of quality antifreeze (ethylene glycol) and water to provide the desired protection.
  19. Run the engine to operating temperature.
  21. Stop the engine and check the coolant level.
  23. Check the level of protection with an antifreeze tester, replace the cap and check for leaks.