Temperature Test Allows monitoring of temperature changes. Thermostat opening temperature can be checked from a cold start. Probe for cool spots in the radiator. Cooling fan switch operation can be monitored.

Radiator Checks Cold spots indicate internal restrictions. Inspect for external restrictions and leaks. Check for loose cooling fins. Salt and road debris can corrode fins and tubes.

Checking Hoses Hoses deteriorate from the inside. Upper radiator hose suffers the most. Check lower hose reinforcement spring.

Checking Fans and Fan Clutches Inspect fan shroud for fit and damage. Damage to belt driven fan can damage water pump and/or radiator. Check fan clutches for oil loss. Replace clutch if it spins with little or no resistance with the engine off.

Electric Cooling Fans Check fan, blades, and mounting assembly. Fan should energize with A/C on and once engine reaches operating temperature. If the fan does not come on, jumper the fan motor to the battery. Follow the service procedures given by the manufacturer.

Testing the Thermostat Should be closed when cold.. Opens when hot. Most are fully open at 195° F (90.5 °C)

Water Pump Checks Noise and leakage are common problems. Common Causes of Water Pump Bearing Failure: A bent fan A missing piece of fan blade A cracked fan blade Fan mounting surfaces that are not flush A worn fan clutch

Testing for Leaks Most common cause of overheating is low coolant levels due to leaks. Hoses, radiator, heater core, water pump, thermostat housing, freeze plugs, transmission oil cooler, head gaskets, and intake gaskets are common leakage points.

Pressure Testing Applies pressure to system for leak test

Leak Detection with Dye Pour dye into cooling system. Run engine to operating temperature. With engine off, inspect with a black light.

Combustion Leak Check Internal leak may be present when there are no visible external leaks but engine is losing coolant or hold pressure. Typically caused by cracked head, head gasket, or warped head.

Testing the Radiator Cap Leaking cap will reduce boiling point and cause an overheating condition.

Water Outlet Can fail from internal corrosion. Improper torquing can warp or break outlet.

Cooling System Service Pressure test the system for leaks. Check coolant condition and strength using a hydrometer. Check radiator cap for proper pressure. Test thermostat for proper opening and closing temperatures.

Cooling System Service (cont’d) Check hoses for leaks and swelling. Check the system with a voltmeter for electrochemical degradation. Check water pump for bearing failure and leaks. Check cooling fans and fan clutch for proper operation.

Cooling System Service (cont’d) Drain coolant below level of hose being replaced. Cut end of old hose. Clean neck of hose fitting . Dip ends of hose in coolant when installing. Do not reuse spring clamps. Install and tighten hose clamps.

Hose Clamps Worn drive clamps often replace spring clamps. Thermoplastic clamps are shrink fit with a heat gun. Readjust a new clamp after a brief run-in period.

Thermostat Always replace with same temperature. Replace the gasket or seal at same time.

Repairing Radiators Repairs depend on radiator construction and the type of damage. Most repairs are made by specialty shops. Plastic tanks are replaced, not repaired.

Replacing the Water Pump Drain the cooling system . Remove parts that interfere with removal. Loosen bolts in a crisscross pattern from the center outward. Follow the procedures given by the manufacturer.

Draining the Coolant Coolant should be changed every two to four years. Drain reservoir and cooling system. Never pour coolant into a sewer or onto the ground.

Flushing the Cooling System Flush the system when coolant is changed and when a water pump is replaced. Power flushing, back flushing, and coolant exchanges force old coolant out and new coolant in. Before using any flush chemical, check to make sure it is safe for the system.

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Refilling and Bleeding Refill with correct type. Determine the total capacity . Refill system and run engine to operating temperature. Remove air trapped in the system. Refill and recheck coolant level and for any leaks.

Special Procedures for Hybrid Vehicles Require special coolants for engine and inverter. Some models use hot coolant storage tanks. Coolant in the radiator could be cold but hot in the storage tank. Follow all manufacturer service and safety procedures.