When adding or changing the fluid in the system, create a 50/50 mixture of high quality ethylene glycol antifreeze and water for 1984-95 vehicles. For 1996 vehicles, use a 50/50 mixture of ethylene based DEX-COOL(r) and water.
See Figures 1, 2, 3, 4, 5 and 6
The fluid level may be checked by observing the fluid level marks of the coolant recovery reservoir or by unscrewing and reading the recovery reservoir dipstick. The level should be between the HOT and COLD mark when the system is at normal operating temperature. When the engine is cold, the fluid level should be above the HOT mark on the reservoir or dipstick, as applicable. Only add coolant to bring the level to the full HOT mark.
cooling system inspectionChecking the Radiator Cap Seal
See Figure 7
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 8
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 move them again.
DRAIN & REFILL
See Figures 9, 10, 11, 12, 13, 14 and 15
- Park the vehicle on a level surface, and allow the engine to thoroughly cool.
- With a cool engine, slowly rotate the radiator cap or radiator surge tank cap, as applicable, counterclockwise to the detent without pressing down on the cap.
- Wait until any remaining pressure is relieved by listening for a hissing sound.
- After all the pressure is relieved, press down on the cap and continue to rotate the cap counterclockwise.
- With a suitable container to catch the fluid under the radiator, open the radiator drain cock.
- If equipped, position a drain pan, then remove all engine block plugs, as applicable.
On VIN P, J and 5 engines, a large amount of coolant will be left in the system after the radiator drain cock has been opened and the coolant drained. A lot of coolant will come pouring out when the knock sensors is removed or thermostat housing separated, as applicable. Avoid contacting the coolant, as much as possible.
For 1992-96 5.7L (VIN P and 5) engines, perform the following:
- If equipped, open the air bleed valves on the thermostat housing and the throttle body unit.
- Position a suitable drain pan under the knock sensors.
- Remove the engine knock sensors from the lower right and left hand side of the engine block.
- If equipped, remove the engine block coolant drain hole plug.
For 1990-95 5.7L (VIN J) engines, perform the following:
- Place a suitable drain pan under the thermostat housing.
- Remove the thermostat from the thermostat housing, being careful not to scratch housing mating surfaces or damage the seal on the thermostat during removal.
- Allow the system to drain completely.
- Close the radiator drain cock and install the engine block drain plug, knock sensors and/or thermostat and housing, as applicable.
Use a 50/50 mixture of water and Ethylene Glycol antifreeze (1984-95 vehicles) or DEX-COOL® (1996 vehicles). Freezing protection should be appropriate for temperatures of -34°F (-37°C).
- Fill the cooling system through the radiator/surge tank neck. If equipped, close the air bleed vent when bubbles disappear and only engine coolant is visible.
- Fill the reservoir assembly to the "COLD" mark. Install the coolant reservoir cap/dipstick.
- Firmly set the parking brake. Run the engine with the radiator cap off, until normal operating temperature is reached.
- With the engine idling, add engine coolant to the radiator until the level reaches the bottom of the radiator fill neck.
On 1988-90 5.7L (VIN 8) engines, when filling the engine coolant system, add 6 engine coolant supplement sealant pellets (GM part no. 3634621 or equivalent) to the system. On 1992-96 5.7L (VIN P) engines, add 6 engine coolant sealant pellets when filling the engine coolant system.
- Install the radiator cap or surge tank cap, as applicable. After running the engine until normal operating temperature is reached, inspect the system for leaks.
The "LOW COOLANT" warning indicator lamp may come on after this procedure. After operating the vehicle so that the engine heats up and cools down three times, this indicator should go out. If the "LOW COOLANT" warning indicator lamp does not go out, or fails to come on at ignition check and the coolant is above "COLD" mark in reservoir, electrical diagnosis performed by a certified technician is required. If at any time the "TEMP" warning indicator lamp comes on, immediate action is required. Turn off the engine and allow the vehicle to cool down. Do not remove the coolant recovery reservoir cap at this time.
FLUSHING & CLEANING THE SYSTEM
The cooling system should be drained, thoroughly flushed and refilled at least every 30,000 miles or 24 months. This operation should be done with the engine cold.
- Drain the cooling system as described earlier in this section.
- Fill the cooling system with warm water and start the engine. Run the engine until normal operating temperature is reached.
- At this point, turn the engine off and again drain the cooling system.
- Repeat this procedure until the fluid draining from the system is nearly colorless.
- Remove, empty and reinstall the coolant recovery reservoir assembly.
- Fill the cooling system with a 50/50 mixture of ethylene glycol antifreeze, as outlined in the previous procedure.