Thermostat, Hoses, Fan Shroud and Accessories
Check that the thermostat is operating correctly. The thermostat should open when the engine reaches approximately 195 degrees F. To verify this, connect a scan tool to the vehicles ALDL Connector and monitor coolant temperature. The coolant temperature should be below 140 degrees F before the start of this test. Start the engine, let idle and observe the coolant temperature. The temperature should rise at a steady rate until the thermostat opens (about 195 degrees F). At this point the coolant temperature may momentarily drop a few degrees, or stay constant for a minute or two. If the thermostat opens at a temperature lower than 190 degrees F or higher than 200 degrees F, it should be replaced.
HOSES
Check that the upper and lower radiator hoses as well as all heater hoses are not collapsed or kinked. Such restrictions can interrupt or reduce the flow of coolant.
COOLANT
Today's vehicles are designed to operate with a 44/56 solution of antifreeze and water for optimum cooling system performance. This gives freeze protection to -20 degrees F. In colder climates a 50/50 solution is recommended for freeze protection to -34 degrees F.
These solutions give the correct cooling system balance of freeze protection, heat dissipation and corrosion protection.
When cooling systems are drained for any reason it is important that the correct concentration of antifreeze be maintained. Increasing or decreasing the antifreeze concentration from the desired mix can have undesirable effects on the system.
Listed here are some useful facts concerning antifreeze concentrations:
^ GM coolant specification 6038-M (P/N 1052103) is recommended for all light and medium duty trucks with gasoline or diesel engines.
^ A 50/50 antifreeze mix increases cooling capacity about 15% over clear water.
^ Maximum freeze protection is obtained at about 69% antifreeze. Higher concentrations actually raise the freeze point.
^ The freeze point of 100% antifreeze is about -8 degrees F.
^ Engine damage from freezing due to very high concentrations of antifreeze is not likely for two reasons.
1. High concentration solutions do not freeze to a solid, but become a heavy slush.
2. High concentrations of antifreeze contract rather than expand at their freezing point.
COOLANT LEVEL
Check the overflow reservoir to see that the radiator and cooling system are filled to the proper level. If the reservoir level is low or is completely empty, check it for leaks.
BELTS
Check that the serpentine belt is routed correctly around all the pulleys. Incorrect routing of the belt may result in the water pump turning in the wrong direction. An illustration of the correct belt routing for the application is on a label located on the fan shroud.
WATER PUMP
Check to see if the water pump is actually moving the coolant. This can be done by observing the coolant flow back to the radiator, by way of the heater hose, through the radiator cap opening. This check can only be made on a warmed-up engine (thermostat open). If there is no coolant being returned to the radiator, the water pump impeller may be slipping on the shaft.
CAUTION: THE RADIATOR CAP SHOULD BE REMOVED FROM A COOL ENGINE ONLY. IF THE RADIATOR IS REMOVED FROM A HOT COOLING SYSTEM, SERIOUS PERSONAL INJURY MAY RESULT.
FAN SHROUD
Check that the fan shroud is correct for the application and that it is not damaged (pieces missing). If the fan, fan clutch and shroud are correct for the application, the fan blades will be positioned partially (half way) inside the fan shroud and partially (half way) outside the fan shroud. In an incorrect assembly, the fan blades will either be too far inside or outside the fan shroud. When the blades are not positioned correctly, the fan will not be able to draw the required amount of air across the radiator, possibly resulting in an overheat at idle.
RADIATOR CORE SUPPORT - C/K models
On models equipped with the 7.4L engine, verify that the radiator core support has the correct opening dimensions. See Dealer Service Bulletin No. 88-338-6B.
BAFFLES AND DEFLECTORS - C/K models
Figure 4:
On models equipped with the 7.4L engine, verify that the lower radiator support baffle has been installed (Figure 4). For additional information see Dealer Service Bulletin No. 88-338-6B. Also verify that the upper radiator air deflector has been installed (Figure 4).
Figure 5:
On models equipped with the 5.7L engine, verify that the front bumper air deflector has been installed (Figure 5).
BAFFLES, DEFLECTORS, PANELS and SEALS - R/V models
Figure 6:
Figure 7:
On R/V models equipped with the 7.4L engine, verify that the radiator baffle has been installed (Figure 6). Also verify that the upper radiator panel has been installed (Figure 7).
Figure 8:
Figure 9:
On R/V models equipped with the 5.7L engine, verify that the front bumper air deflector has been installed (Figure 8). On models with air conditioning, verify that both left and right radiator seals have been installed (Figure 9).
AFTERMARKET ACCESSORIES
Verify that there are no aftermarket transmission oil coolers or other aftermarket accessories mounted in front of the radiator or condenser. Accessories mounted in this area reduce or alter air flow required for proper cooling. Relocate all such aftermarket accessories to an area where air flow to the radiator or condenser will not be affected.