GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Cooling System

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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 -20ºF (-29ºC) (-32ºF/36ºC in Canada).

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.

FLUID RECOMMENDATIONS



Coolant mixture in 1994-95 pick-ups 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.

The 1996-99 models use a 50/50 mixture of water and DEX-COOL-coolant. This silicate free coolant is orange in color and does not require maintenance for 5 years or 100,000 miles (166,000 km). If additional coolant needs to be added to the system, use only DEX-COOL-or a silicate free orange coolant meeting GM spec 6277M. If another coolant type is added, the advantage of the prolonged maintenance period is lost.

FLUID LEVEL CHECK



See Figures 1, 2, 3, and 4



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Fig. Fig. 1: Be sure the rubber gasket on the radiator cap has a tight seal



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Fig. Fig. 2: Periodically remove all debris from the radiator fins



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Fig. Fig. 3: Cutaway view of a typical cooling system flow



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Fig. Fig. 4: Cooling systems should be pressure tested for leaks periodically

  1. Check the level on the see-through expansion tank.
  2.  


CAUTION
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 the proper type of coolant (see fluid recommendations) through the expansion tank to the proper level. 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 vehicles; the heater core can freeze if it isn't protected. Coolant should be added through the coolant recovery tank, not the radiator filler neck.
  2.  


WARNING
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 at 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.
 

DRAINING AND FLUSHING



See Figures 5 through 11



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Fig. Fig. 5: To drain the cooling system, open the radiator petcock-1994 model shown, others similar



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Fig. Fig. 6: Read the instructions on the radiator cap before removing it-1996 model shown, others similar



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Fig. Fig. 7: Remove the radiator cap-1994 model shown, others similar



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Fig. Fig. 8: Add a 50/50 mix of ethylene glycol, or other suitable antifreeze, and water-1994 model shown, others similar



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Fig. Fig. 9: Removing the cap from the coolant recovery tank-1996 model shown, others similar



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Fig. Fig. 10: Adding coolant to the recovery tank-1996 model shown, others similar



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Fig. Fig. 11: As this label indicates, 1996 and newer models use DEX-COOL-coolant

The cooling system in your vehicle 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. On 1994-95 models, this operation should be performed every 30,000 miles (48,000 km) or once a year (whichever comes first). On 1996-99 models, this service should be performed every 100,000 miles (166,000 km) or once every 5 years. Keep in mind this holds true only if DEX-COOL-or a silicate free orange coolant meeting GM spec 6277M has been used. If another type of coolant has been used in this system, then this operation should be performed every 30,000 miles (48,000 km) or once a year (whichever comes first).


CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine 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 quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is 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.
  2.  
  3. Close the petcock or reconnect the lower hose and fill the system with water-hot water if the system has just been run.
  4.  
  5. Add a can of quality radiator flush to the radiator or recovery tank, following any special instructions on the can.
  6.  
  7. Idle the engine as long as specified on the can of flush, or until the upper radiator hose gets hot.
  8.  
  9. Drain the system again. There should be quite a bit of scale and rust in the drained water.
  10.  
  11. Repeat this process until the drained water is mostly clear.
  12.  
  13. Close all petcocks and connect all hoses.
  14.  
  15. Flush the coolant recovery reservoir with water and leave empty.
  16.  
  17. Determine the capacity of your truck's cooling system (see the Capacities chart in this guide). Fill the cooling system with the proper type of coolant (refer to fluid recommendations).
  18.  
  19. Run the engine to operating temperature, then stop the engine and check for leaks. Check the coolant level and top up if necessary.
  20.  
  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 +5ºF (-15ºC), for example.
  22.  

 
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