Engine Cooling Fan GMC Pickup R1500

DESCRIPTION

The basic liquid cooling system consists of a radiator, water pump, thermostat, electric or belt-driven cooling fan, pressure cap, heater, and various connecting hoses and cooling passages in the block and cylinder head.

DRAINING

Remove radiator cap and open heater control valve to maximum heat position. Open drain cocks or remove plugs in bottom of radiator and engine block. In-line engines usually have one plug or drain cock, while "V" type engines will have 2, one in each bank of cylinders.

CLEANING

A good cleaning compound removes most rust and scale. Follow manufacturer's instructions in the use of cleaner. If considerable rust and scale has to be removed, cooling system should be flushed. Clean radiator air passages with compressed air.

FLUSHING

1. Back flushing is an effective means of removing cooling system rust and scale. The radiator, engine and heater core should be flushed separately.
2. To flush radiator, connect flushing gun to water outlet of radiator and disconnect water inlet hose. To prevent flooding engine, use a hose connected to radiator inlet. Use air in short bursts to prevent damage to radiator. Continue flushing until water runs clear.
3. To flush engine, remove thermostat and replace housing. Connect flushing gun to water outlet of engine. Flush using short air bursts until water runs clean. Flush heater core as described for radiator. Ensure heater control valve is set to maximum heat position before flushing heater.

REFILLING

To prevent air from being trapped in engine block, engine should be running when refilling cooling system. After system is full, continue running engine until thermostat is open, then recheck fill level. Do not overfill system.

Scheme 1

1. Visually inspect thermostat for corrosion and proper sealing of valve and seat. If okay, suspend thermostat and thermometer in a 50/50 mixture of coolant and water. (Scheme 1) Do not allow thermostat or thermometer to touch bottom of container. Heat water until thermostat just begins to open.
2. Read temperature on thermometer. This is the initial opening temperature and should be within specification. Continue heating water until thermostat is fully open and note temperature. This is the fully opened temperature. If either reading is not to specification, replace thermostat. (Scheme 1): Testing Thermostat in Anti-Freeze/Water Solution NOTE: A pressure tester is used to check both radiator cap and complete cooling system. Test components as follows, following tool manufacturer's instructions.

Pressure Testing Radiator Cap

Visually inspect radiator cap, then dip cap into water and connect to tester. Pump tester to bring pressure to upper limit of cap specification. If cap fails to hold pressure, replace cap.

Testing Radiator Pressure Cap. Scheme 2

Note. Wet cap gasket before testing.

Scheme 3

1. With engine off, wipe radiator filler neck seat clean. Fill radiator to correct level. Attach tester to radiator and pump until pressure is at upper level of radiator rating.
2. If pressure drops, inspect for external leaks. If no leaks are apparent, detach tester and run engine until normal operating temperature is reached. Reattach tester and observe. If pressure builds up immediately, a possible leak exists from a faulty head gasket or crack in head or block. NOTE: Pressure may build up quickly. Release any excess pressure or cooling system damage may result.
3. If there is no immediate pressure build up, pump tester to within system pressure range (on radiator cap). Vibration of gauge pointer indicates compression or combustion leak into cooling system. Isolate leak by shorting each spark plug wire to cylinder block. Gauge pointer should stop or decrease vibration when leaking cylinder is shorted. (Scheme 3): Pressure Testing Cooling System

This unit consists of a torque controlled clutch driven fan. The system consists of a silicone filled coupling which connects fan to pulley. Fan drive is operated by a control valve which is governed by a temperature sensitive bi-metallic coil or strip. The control valve maintains flow of silicone through drive.

When cooling air temperature is low, fan drive limits fan speed. High air temperature causes bi-metallic to allow greater flow of silicone to enter drive. This increases drag between driven member and driving member, resulting in higher fan speed and increased cooling.

Scheme 4

1. When engine overheats or insufficient cooling caused by air conditioning or other components occurs, fan drive and thermostatic control must be tested. Start with cool engine to ensure complete fan drive disengagement. Cover radiator grille to induce high engine temperature.
2. Start engine. Operate at 2000 RPM and turn on air conditioning (if equipped). Fan noise will increase when fan drive engages. It will take 5-10 minutes for fan to become engaged. While operating engine under these conditions, observe temperature gauge or light to prevent overheating. If vehicle overheats, remove cover from radiator grille.
3. As soon as drive engages, remove radiator grille cover and turn air conditioning off. After several minutes fan drive should disengage. This can be determined by reduction in fan speed and noise. If fan drive fails to function as described, it should be replaced.
4. Fan drive should also be replaced if shaft seal is leaking fluid. If noise or roughness can be felt while turning by hand, replace drive. Frozen unit must be replaced. (Scheme 4): Thermal Control Fan Drive Unit NOTE: Rotation speed will vary with engine temperature.

This unit is same as thermostatically controlled fan drive except it is not controlled by a bimetallic temperature sensitive coil. Fan drive allows fan to be driven in normal manner at low speeds while higher engine speed limits rotational speed of fan to predetermined rate. Silicone in drive housing provides more positive drive at lower speeds and allows greater slippage between driven member and driving member at higher engine speeds.

TESTING

If engine overheats during low speed or idle operation, increase engine speed to about 1000 RPM in Neutral. If condition is not corrected by increasing engine speed, replace fan drive unit. All units are non-adjustable.

ELECTRIC COOLING FAN

Note. Models equipped with 7.4L V8 engine and A/C may contain an optional electric cooling fan. No specifications are available from manufacturer.