Cooling System Testing, Maintenance, and Repair Chapter 40
Contents (12 Topics) • Cooling system diagnosis • Cooling system problems • Water pump service • Thermostat service • Cooling system hose service • Radiator and pressure cap service
Contents • Fan belt service • Engine fan service • Freeze plug service • Coolant service • Flushing a cooling system • Temperature gauge service
Cooling System Problem Diagnosis • Gather information: • Talk to the owner or service writer to find out as much as possible about the symptoms • A Cooling System Diagnosis Chart in the service manual can be very helpful when problems are difficult to locate and correct.
On-Board Diagnostics • Cooling-related problems may set a diagnostic trouble code on some systems if temperatures seem out of range. • use a scan tool to analyze the system • MIL lamp may be on • data will indicate engine temperature • even failure to bleed a system of air could cause erratic temperature sensing
Cooling System Functions often monitored by the OBD II system: • Coolant Temperature • Engine oil Temperature • Belt Tension • Other related functions
Visual Inspection of Cooling System • Perform a visual inspection for: • coolant leaks • loose or missing fan belts • low coolant level • water pump noises • plugged radiator fins • coolant in the oil (oil looks milky) • combustion leakage into coolant
Cooling System Problems • Coolant leaks • Overheating • Overcooling
Coolant Leaks • External leaks • most common • show up as wet, discolored areas on parts • Internal leaks • caused by cracked block, head or blown head gasket
Cooling System Problems A blown head gasket can allow combustion gases to enter the coolant, a combustion leak test will verify this type of problem
Cooling System Problems Mineral deposits in water jackets can prevent proper heat transfer
Cooling System Problems A cracked part or blown gasket can allow coolant to leak into the engine oil and cause a milky white substance to form in the valve covers
Cooling System Pressure Tester One of the most commonly used and important cooling system testing devices!
Cooling System Pressure Test TO AVOID SERIOUS BURNS,NEVER REMOVE A RADIATOR CAP WHEN ENGINE IS HOT! • Install pressure tester on filler neck • Pump the tester to pressurize system Use cap rating for maximum psi to avoid serious damage to cooling system • Low air pressure is forced into the system • causes coolant to pour or drip from any leak
Combustion Leak Test • Should be performed when indications of a blown head gasket, cracked head, or cracked block are suspected. • Checks for the presence of combustion gases in the coolant • Place combustion leak tester on filler neck • Start engine and squeeze tester bulb, pulling air through test fluid • If combustion gases are present in the radiator, fluid changes color (from blue to yellow)
Combustion Leak Test Combustion leakage can makethe engine overheat
Combustion Leak Test Leak testing with an exhaust gas analyzer. HC reading indicates leakage
Causes of Overheating • Low coolant level • Rust or scale accumulation in coolant • Stuck thermostat • Retarded ignition • Loose fan/water pump belt • Bad water pump • Collapsed lower hose • Missing fan shroud or fan problems • Ice in the coolant
Causes of Overcooling • Stuck thermostat (open) • Locked fan clutch • Shorted fan switch Indications of Overcooling • Heater does not get hot • Temperature gage remains cold • Poor fuel economy
Water Pump Service • A bad pump may leak, fail to circulate coolant, or produce a grinding sound • Common Causes of Water Pump Failure: • rust in the cooling system • lack of coolant • overtightened belts
Visual Inspection(Checking for worn Water Pump Bearings) Pump shaft should not wiggle or leak
Visual Inspection Watch for leakage from bleed holesA mechanic’s stethoscope can be used to pinpoint failing water pump bearings
Removing a Water Pump • Unbolt brackets and components • air-conditioning compressor • power steering pump • alternator • Remove pump • Scrape off old gasket or sealer material • Do not use excessive force when separating a water pump from an engine because you may gouge the sealing surfaces!
Installing a New Water Pump(Most Technicians prefer to install a new water pump rather than rebuilding the old one, because it is more cost effective and comes with a better warranty) • Fit pump onto the engine • Start all bolts by hand • Torque all fasteners to specifications • Use sealer where specified • Install the other components
Installing a Water Pump A. Gasket held in place by sealer B. Sealer only Note: Be sure to use the correct sealer to adhere the water pump gasket to the water pump to avoid coolant leakage
Water Pump This pump uses an O-ring sealinstead of sealer or gasket
Installation Tightening water pump bolts evenly to proper torque specs
Thermostat Service • A stuck thermostat can cause engine overheating or overcooling • Stuck open–overcooling • loss of efficiency, power, mileage • high emissions • Stuck closed–overheating • engine damage
Thermostat Testing • Watch the coolant through the opening in the radiator neck • Cold engine, coolant should not flow • Hot engine, coolant should begin to circulate past the opening • Use a digital thermometer to monitor the temperature of the thermostat housing and outlet hose. If the housing is reaching engine operating temperature but the outlet hose stays cool, the thermostat is not opening and needs to be replaced
Thermostat and Housing Caution: Over tightening the thermostat housing can cause it to warp or crack and create coolant leakage
Thermostat and Housing Some manufacturers use an O-ring seal which should be replaced anytime the thermostat is removed
Bleeding the Cooling System • A bleed valve is sometimes provided to help eliminate trapped air in the cooling system • Cars with low hood lines require a bleed screw to empty air pockets • Trapped air can cause overheating or a buildup of heat called ahot spot
Bleeding the Cooling System • Fill the system • Start and warm the engine • Crack open the bleed screw until all air is purged from the system • Never remove a cooling system bleed screw or any clamp on a hot, pressurized system!
Cooling System Hose Service Hoses deteriorate and become soft and mushy or hard and brittle and should be replaced
Hose Replacement • Loosen clamp, • Twist and pull hose off • Clean fitting • Install new hose and clamp • Check for leaks
Radiator and Pressure Cap Service
Inspecting the Radiator and Pressure Cap Conditions that can limit airflow through the radiator • Inspect radiator fins for debris and rot • Make sure the shroud is in place • Perform a Radiator Cap Pressure Testwhich measures cap opening pressure • checks sealing washer condition TO AVOID SERIOUS BURNS,NEVER REMOVE A RADIATOR CAP WHEN ENGINE IS HOT!
Radiator Removal • Place a catch pan under the cool radiator • Open the petcock to drain system • Disconnect hoses and oil cooler lines • Disconnect wires going to sensors and fan motors • Remove any brackets and radiator
Radiator Repair • Most repairs are done by a radiator shop • Radiator shops disassemble, clean, repair, reassemble and test radiators • When installing radiator, make sure the rubber mounts are in place
Fan Belt Service • An over tightened fan/water pump belt can cause water pump bearing failure • A loose fan belt will slip and squeal and may cause overheating • Inspect the condition and tension • Use a belt tension gauge to adjust belts
Engine Fan Service • A faulty fan can cause overheating, overcooling, vibration and water pump damage • Check for bent blades, cracks or fluid leakage
Testing a Thermostatic Fan Clutch • Start the engine • When cold, fan should slip • When warm, clutch should engage • you should hear the rush of air
Electric Cooling Fan Most electric cooling system fans are controlled by a temperature switch or sensor located in the radiator, thermostat housing, or engine block. When the engine is cold, the fan stays off, which saves on fuel and helps the engine warm-up more quickly. When the engine is warm the fan only comes on when necessary, which also helps improve fuel economy.
Testing an Electric Cooling Fan A. Check for power to the fan, engine hot B. Switch open when cold, closed when hot C. Test using a test lamp or digital volt meter