© goodheart-willcox co., inc. cooling system diagnosis cooling system problems thermostat...


Cooling system diagnosis Cooling system problems Thermostat service Cooling system hose service Radiator and pressure cap service Fan belt service Coolant service Flushing a cooling system


Gather information: talk to the owner or service writer to find

out as much as possible about the symptoms

diagnosis charts in the service manual can be very helpful


On-Board Diagnostics

Cooling-related problems may set a diagnostic trouble code on some systems 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


Inspecting 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


Common 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



Mineral deposits in water jackets can

prevent proper heat transfer



A cracked part or blown gasket can

allow coolant to leak into the engine oil


Cooling System Pressure Test

Low air pressure is forced into the system causes coolant to pour or drip from any

leak

Install pressure tester on filler neck Pump the tester to pressurize system Maximum 14 psi, (96 kPa) or cap rating


Cooling System Pressure Test


Combustion Leak Test

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


Combustion Leak Test

Combustion leakage can make

the engine overheat


Causes of Overheating

Low coolant level Rust or scale accumulation in water jacket Stuck thermostat Delayed ignition Loose fan belt Bad water pump or collapsed lower hose Missing fan shroud or fan problems

Causes of Overcooling

Stuck thermostat (open)Locked fan clutchShorted fan switch


A bad pump may leak, fail to circulate coolant, or produce a grinding sound

Causes: rust in the cooling system lack of coolant overtightened belts


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


Thermostat and Housing


Thermostat Replacement


Thermostat and Housing

Special O-ring seal should be replaced anytime the thermostat is removed


Bleeding the Cooling System

A bleed valve is sometimes provided Cars with low hood lines require a bleed

screw to empty air pockets Trapped air can cause overheating or

damage from hot spots (buildup of heat)



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!!!


Common Hose

Problems

Hoses deteriorate and become soft and mushy

or hard and brittle


Hose ReplacementA. Loosen clamp, twist and pull hose offB. Clean fittingC. Install new hose and clamp, check for

leaks


Inspecting the Radiator andPressure Cap

Inspect radiator fins for debris and rot Make sure the shroud is in place Perform pressure cap test

measures cap opening pressure checks sealing washer condition


Pressure Testing a Radiator Cap


Radiator Removal


A loose fan belt will slip and squeal may cause overheating

Inspect the condition and tension Use a belt tension gauge to adjust belts

A faulty fan can cause overheating, overcooling, vibration and water pump damage

Check for bent blades, cracks or fluid leakage


Coolant should be checked and changed at regular intervals

Breaks down and becomes acidic Rust preventative properties are lost


Changing Coolant


Checking Coolant Level

Coolant should be even with correct marking on reservoir


Checking Coolant Level

Coolant should be 1” below the top

of the tank


Testing Coolant Strength

Measures the concentration of antifreeze compared to water

Determines freeze protection Tool used:

cooling system hydrometer


HydrometerWhen filled, pointer will float to indicate

freeze protection


Cleans rust and scale from the system May involve running a cleaning

chemical through the system Three Methods:

1. fast flushing 2. reverse flushing 3. chemical flushing


1. Fast Flushing


2. Reverse Flushing


3. Chemical Flushing

Used when scale buildup is causing overheating

Chemical cleaner is added to the coolant

Engine is operated for a specific amount of time

System is flushed with water

© goodheart-willcox co., inc. cooling system diagnosis cooling system problems thermostat...

Documents

coolant slide

cooling system slide

overcooling slide

helpful slide

engine oil slide

inspecting cooling system

system of air

head gasket slide