Engine Cooling System Honda Prelude II

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, vehicles use a thermostatically controlled electric fan.

Some models may use a thermostatic vacuum switch to advance ignition timing in the event of overheating. Models use a coolant recovery system to prevent loss of anti-freeze.

DRAINING

Remove radiator cap and open heater control valve to maximum heat position. Open drain cocks or remove plugs in bottom of radiator and in engine block. In-line engines have one plug or cock.

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, flushing should be used. Clean radiator air passages by blowing 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 engine. Use air in short bursts only, as this will prevent damage to radiator. 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 the engine block. After system is full, continue running engine until thermostat is open, then recheck fill level. Do not overfill system. On models with a bleed bolt on or near the thermostat housing, open bleed bolt to release air from system after filling.

Scheme 1

1. Remove thermostat from housing, located at end of cylinder head, opposite drive belts. Visually inspect thermostat for corrosion and proper sealing of valve and seat. If satisfactory, suspend thermostat and a thermometer in a container with a 50/50 mixture of anti-freeze and water. (Scheme 1)
2. 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. (Scheme 1): Testing Thermostat in Anti-Freeze/Water Solution
3. Read temperature on thermometer. This is the initial opening temperature and should be within specifications. Continue heating water until thermostat is fully open and note temperature. This is the fully opened temperature. If either reading is outside of specifications, replace thermostat, as it is not adjustable.

PRESSURE TESTING

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

Radiator Cap

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

Testing Radiator Pressure Cap. Scheme 2

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 limit 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 obtained. Reattach tester and observe. If pressure builds up immediately, a possible leak exists from a faulty head gasket or crack in head or block.
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.
4. Remove engine and transmission (automatic only) oil dipsticks and check if water drops appear in oil. If so, a serious internal leak is indicated. If all checks are negative and system holds pressure for 2 minutes, there are no serious leaks in system.

Pressure Testing Cooling System. Scheme 3

ANTI-FREEZE CONCENTRATION

Note. On models using aluminum engines or cooling system components, refer to Owners Manual for anti-freeze requirements and recommendations. Aluminum components require a different formulation of anti-freeze to prevent corrosion.

On all cooling systems, test anti-freeze concentration using anti-freeze tester. Tester should have a temperature-compensating feature, as failing to take temperature into consideration could cause an error as large as 30°F (16°C). Follow tester manufacturer's instructions for correct use of tester.

A coolant recovery system differs from other cooling systems in that an overflow bottle is connected to the radiator overflow hose. Overflow bottle is transparent or translucent to permit checking of coolant level without removing radiator cap. No adjustment or test is required except 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 the system. Vacuum draws coolant, stored in overflow bottle, back into radiator. In a properly maintained cooling system, the only coolant losses will be through evaporation. Overflow bottle captures and releases coolant according to temperature. (Scheme 4)

Identifying Coolant Recovery System (Typical). Scheme 4

Electrically-driven fans are actuated by thermal relay switches. Thermal switches turn fan motor on when necessary and shut fan motor off when not needed. Air conditioned vehicles are equipped with over-ride switches. These switches turn fan motor on whenever air conditioning system is operating. When system is turned off, fan motor control is returned to thermal relay.

Identifying Thermostatically Controlled Electric Fan (Typical). Scheme 5

TESTING

Disconnect fan motor wire connector and connect it with 14 gauge wire to a good 12-volt battery. If fan runs, motor is okay. This indicates car battery, thermal switch, radiator fan switch, coolant relay, timer relay, coolant temperature switch, or A/C relay may be defective. If fan motor does not run when connected directly to a good battery, replace fan motor.

Note. To avoid premature cooling system wear, always use the manufacturer's recommended coolant products and coolant mixture ratios.

COOLING FAN THERMOSWITCH

On Accord and Prelude models, thermoswitch comes on at 187-199°F (87-93°C), and goes off at 181-185°F (83-85°C). On Civic models, thermoswitch comes on at 191-196°F (88.5-91.5°C), and goes off at 186-188°F (85.5-86.5°C).

On all models, radiator cap pressure relief valve opens at approximately 11-15 psi (.77-1.05 kg/cm 2 ).

THERMOSTAT

On Accord and Prelude models, standard thermostats have primary and secondary opening stages. Primary begins opening at 176-183°F (80-84°C), secondary begins opening at 181-187°F (83-87°C), and thermostat fully opens at 203°F (95°C).

Optional thermostat on Accord and Prelude models begins opening at 187-194°F (86-90°C), and fully opens 212°F (100°C). On Civic models, thermostat begins opening at 169-172°F (76-78°C), and fully opens at 196°F (91°C).

COOLANT CAPACITY