Engine Cooling Fan GMC Vandura I

DESCRIPTION

The basic liquid cooling system consists of a radiator, water pump, thermostat, cooling fan, pressure cap, heater, if equipped, and various connecting hoses and cooling passages in the block and cylinder head. In addition, many vehicles use a fan clutch, which may incorporate a thermostatic control, or a flexible blade fan, or both, to reduce noise and power requirements at high engine speeds. Some models, with exhaust emission control, use a thermostatic vacuum switch to advance ignition timing in the event of overheating. As most new models require the use of a permanent, year round (ethylene glycol) type anti-freeze, coolant recovery systems are being used more commonly to prevent coolant loss.

DRAINING

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

CLEANING

A good cleaning compound will remove most rust and scale. Follow manufacturer's instructions in the use of the cleaner. If considerable rust and scale will have to be removed, flushing will be necessary. Clean radiator air passages by blowing out with compressed air from back to front of radiator.

FLUSHING

1. Back flushing is a very effective means of removing rust and scale from a cooling system. For best results 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. Use a leadaway hose, connected to radiator inlet, to prevent flooding the engine. Use air in short bursts only, as a clogged radiator could be easily damaged. Continue flushing until water runs clear.
3. To flush engine, first remove thermostat and replace housing. Connect flushing gun to water outlet of engine. Disconnect heater hoses from engine. Flush using short air bursts until water runs clean. Flush heater core as described for radiator. Make sure heater valve is set to maximum heat position before flushing heater.

REFILLING

Engine should be running while refilling cooling system to prevent air from being trapped in engine block. After system is full, continue running engine until thermostat is open, then recheck fill level. Do not overfill system. Refer to COOLING SYSTEM SPECIFICATIONS article in this section.

Thermostat

Visually inspect thermostat for corrosion and proper sealing. If this is satisfactory, suspend thermostat and a thermometer in a container of water. Do not allow either thermostat or thermometer to touch bottom of container as this concentration of heat could cause an incorrect reading. Heat water until thermostat just begins to open. If thermostat does not open, replace.

Testing Thermostat. Scheme 1

Note. Thermostat should open as water is heated.

Note. A pressure testing tool is used to test both radiator cap and complete cooling system. Test as follows, or follow tool manufacturer's instructions.

Pressure Testing Radiator Cap

Visually inspect radiator cap, dip in water and connect to tester. Pump tester to bring pressure to upper limit of cap specification. Refer to COOLING SYSTEM SPECIFICATIONS article in this section. If cap fails to hold pressure within given specification, replace cap.

Testing Radiator Pressure Cap. Scheme 2

Note. Attach cap to tester and apply pressure.

Pressure Testing Cooling System

1. With engine stopped, wipe radiator filler neck seat clean. Fill radiator to correct level. Attach cooling system tester to radiator and pump until pressure is at upper level of radiator rating. If pressure drops, inspect for internal leaks.
2. If no leaks are apparent, detach tester and run engine until normal operating temperature is reached. Reattach tester and pump until pressure reaches approximately 7 psi (.5 kg/cm 2 ). Race engine. If needle on tester fluctuates, it indicates a combustion leak.
3. If needle does not fluctuate, race engine a few more times and check for water at tailpipe. Excessive water would indicate a faulty head gasket, cracked block or cylinder head near exhaust ports. Remove oil dipstick and if water globules appear in the oil, a serious internal leak is indicated. NOTE: Pressure may build up quickly. Release any pressure above the limit of pressure cap specifications or cooling system damage may result.

Anti-Freeze Concentration

Test anti-freeze concentration. The tester should have a temperature compensating feature. Failure to take temperature into consideration could cause an error as large as 30°F in freeze or overheating protection. Follow manufacturer's instructions for correct use of tester.

Pressure Testing Cooling System. Scheme 3

Note. Be sure tester has a temperature compensating feature.

A coolant recovery system differs from a normal cooling system in that an overflow bottle is connected to the radiator overflow hose. The overflow bottle is transparent or translucent to permit checking of coolant level without removing radiator cap. No adjustment or test is required beyond keeping vent hole or hose clean and checking pressure relief of radiator cap.

OPERATION

As coolant temperature rises and pressure in system exceeds pressure relief valve of radiator cap, excess coolant flows into overflow bottle. As engine cools and coolant contracts, vacuum is formed in system, drawing coolant, stored in overflow bottle, back into radiator. In a properly maintained cooling system, the only coolant losses will be through evaporation.

Coolant Recovery System. Scheme 4

Note. System should eliminate loss of coolant.

The radiator cap consists of a pressure valve and a vacuum valve. The cap has several different functions: It prevents coolant loss when vehicle is in motion; prevents impurities from entering cooling system minimizing corrosion; allows atmospheric pressure to eliminate the vacuum that occurs in system during cool down; and raises coolant boiling point approximately 2°F per psi of pressure by maintaining a constant cooling system pressure. Refer to COOLING SYSTEM SPECIFICATIONS article in this section.

Radiator Cap Operation. Scheme 5

Note. Cap should maintain constant cooling pressure in system.

This unit consists of a thermostatically controlled fluid fan and torque control clutch. The thermal control drive is a silicone filled coupling connecting the fan to the fan pulley. The drive is operated by a control valve and the control valve is operated by a temperature sensitive bimetal coil or strip. The control valve maintains the flow of silicone through the clutch. During periods of operation when radiator discharge air temperature is low, the fan clutch limits the fan speed. High radiator discharge air temperature causes bimetal to allow a greater flow of silicone to enter the clutch. This increases the drag between the driven member and driving member, resulting in a higher fan speed and increased cooling.

TESTING

In cases of engine overheating or insufficient air conditioning, proceed as follows

Scheme 6

1. Start with a cool engine to ensure complete fan clutch disengagement. Cover radiator grille sufficiently to induce high engine temperature.
2. Start engine and operate at 2000 RPM and turn on air conditioning, if equipped. A fan roar will be noticed when fan clutch engages. It will take 5-10 minutes for fan to become engaged. While operating engine under these conditions, observe temperature light to prevent overheating. If hot light comes on, remove cover from radiator grille.
3. As soon as clutch engages, remove radiator grille cover and turn air conditioning off to assist in engine cooling. After several minutes fan clutch should disengage. This can be determined by a reduction in fan speed and roar. If fan fails to function as described, it should be replaced. (Scheme 6): Thermal Control Fan Drive Unit NOTE: Rotation speed will vary with engine temperature.

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

In case of engine overheating during low speed or idle operation, increase engine speed to approximately 1000 RPM in neutral gear. If condition is not corrected by increasing engine speed, replace fan drive unit with a unit that is known to be operating properly and test by operating vehicle under same conditions. Replace unit assembly if trouble is corrected with test unit. All units are non-adjustable. Replace, if unit is damaged or operating improperly.

This unit is a fixed blade assembly designed to flex the blades as the engine RPM increases. As RPM increases, blade pitch decreases, saving power and decreasing noise level. No adjustment or test is required beyond keeping fan belt adjusted to proper tension and ensuring that unit is not damaged.

Flex-Blade Fan. Scheme 7

Note. Blades should flex as engine RPM increases.