GM Full-Size Trucks 1988-1998 Repair Information

Cooling System


See Figures 1, 2, 3, 4 and 5

The cooling system was filled at the factory with a high quality coolant solution that is good for year around operation and protects the system from freezing down to -20°F (-29°C) (-32°F/36°C in Canada). It is good for two full calendar years or 24,000 miles (38,500 km), whichever occurs first, provided that the proper concentration of coolant is maintained.

The hot coolant level should be at the FULL HOT mark on the expansion tank and the cold coolant level should be at the FULL COLD mark on the tank. Do not remove the radiator cap to check the coolant level.


On 1988-95 models, the coolant mixture in Chevy/GMC trucks is 50/50 ethylene glycol and water for year round use. Use a good quality anti-freeze with water pump lubricants, rust inhibitors and other corrosion inhibitors along with acid neutralizers.

On 1996-98 models, Use a 50/50 mixture of DEX-COOL® coolant and water. Do not mix any other type of coolant with the DEX-COOL® as they are incompatible and may cause damage to the cooling system.

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Fig. Fig. 1: The system should be pressure-tested once a year

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Fig. Fig. 2: Remove any debris from the radiator's cooling fins

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Fig. Fig. 3: Coolant condition can be checked with an inexpensive tester

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Fig. Fig. 4: Check the condition of the radiator cap gasket and seal

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Fig. Fig. 5: Inspect coolant for contamination


  1. Check the level on the see-through expansion tank.

The radiator coolant is under pressure when hot. To avoid the danger of physical harm, coolant level should be checked or replenished only when the engine is cold. To remove the radiator cap when the engine is hot, first cover the cap with a thick rag, or wear a heavy glove for protection. Press down on the cap slightly and slowly turn it counterclockwise until it reaches the first stop. Allow all the pressure to vent (indicated when the hissing sound stops). When the pressure is released, press down on the cap and continue to rotate it counterclockwise. Some radiator caps have a lever for venting the pressure, but you should still exercise extreme caution when removing the cap.

  1. Check the level and, if necessary, add coolant through the expansion tank to the proper level. Use a 50/50 mix of ethylene glycol anti-freeze and water. Alcohol or methanol base coolants are not recommended. Anti-freeze 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 trucks; the heater core can freeze if it isn't protected. Coolant should be added through the coolant recovery tank, not the radiator filler neck.

Never add large quantities of cold coolant to a hot engine! A cracked engine block may result!

Each year the cooling system should be serviced as follows:

Wash the radiator cap and filler neck with clean water.
Check the coolant for proper level and freeze protection.
Have the system pressure tested 15 psi. (103 kPa), If a replacement cap is installed, be sure that it conforms to the original specifications.
Tighten the hose clamps and inspect all hoses. Replace hoses that are swollen, cracked or otherwise deteriorated.
Clean the frontal area of the radiator core and the air conditioning condenser, if so equipped.


The cooling system in you truck accumulates some internal rust and corrosion in its normal operation. A simple method of keeping the system clean is known as flushing the system. It is performed by circulating a can of radiator flush through the system, and then draining and refilling the system with the normal coolant. Radiator flush is marketed by several different manufacturers, and is available in cans at auto departments, parts stores, and many hardware stores. This operation should be performed every 30,000 miles (48,000 km)or once a year.

When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol anti-freeze, 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. Drain the existing anti-freeze and coolant. Open the radiator and engine drain petcocks (located near the bottom of the radiator and engine block, respectively), or disconnect the bottom radiator hose at the radiator outlet.
  3. Close the petcock or reconnect the lower hose and fill the system with water-hot water if the system has just been run.
  5. Add a can of quality radiator flush to the radiator or recovery tank, following any special instructions on the can.
  7. Idle the engine as long as specified on the can of flush, or until the upper radiator hose gets hot.
  9. Drain the system again. There should be quite a bit of scale and rust in the drained water.
  11. Repeat this process until the drained water is mostly clear.
  13. Close all petcocks and connect all hoses.
  15. Flush the coolant recovery reservoir with water and leave empty.
  17. Determine the capacity of your truck's cooling system (see Capacities specifications in this guide). Add a 50/50 mix of ethylene glycol anti-freeze and water to provide the desired protection.
  19. Run the engine to operating temperature, then stop the engine and check for leaks. Check the coolant level and top up if necessary.
  21. Check the protection level of your anti-freeze mix with an anti-freeze tester (a small, inexpensive syringe type device available at any auto parts store). The tester has five or six small colored balls inside, each of which signify a certain temperature rating. Insert the tester in the recovery tank and suck just enough coolant into the syringe to float as many individual balls as you can (without sucking in too much coolant and floating all the balls at once). A table supplied with the tester will explain how many floating balls equal protection down to a certain temperature (three floating balls might mean the coolant will protect your engine down to +5°F (-15°C), for example.