Chemical flushing is needed when a scale buildup in the system is causing engine overheating. Add the chemical cleaner to the coolant. Run the engine at fast idle for about 20 minutes. Wait for the engine to cool. Then drain out the coolant and cleaner solution. Using a garden hose, flush out the loosened rust and scale. Continue to flush until the water runs clear.

CAUTION Always follow manufacturer's instructions when using a cooling system cleaning agent. Wear protective gloves and goggles when handling cleaning agents. Chemicals may cause eye and skin burns.

Antifreeze Service

Antifreeze should be checked and changed at regular intervals. After prolonged use, antifreeze will break down and become very corrosive. It can lose its rust preventative properties and the cooling system can fill rapidly with rust.

A visual inspection of the antifreeze will help determine its condition. Rub your lingers inside the radiator filler neck. Check for rust, oil (internal engine leak), scale, or transmission fluid (leaking oil cooler). 6-16 Also check to find out how long the antifreeze has been in service. If contaminated or too old, replace the antifreeze. If badly rusted, you may need to flush the system. Antifreeze should be changed when contaminated or when 2 years old. Check the service manual for exact change schedules.

Antifreeze strength is a measurement of the concentration of antifreeze compared to water. It determines the freeze-up protection of the solution. There are two devices used to check antifreeze strength - the antifreeze hydrometer and the refractometer.

The antifreeze hydrometer is used to measure the freezing point of the cooling system. A squeeze and release bulb draws coolant into the tester, and a needle floats to show the freeze protection point.

With the refractometer, you draw coolant into the tester. Then place a few drops of coolant on the measuring window (surface). Aim the tester at a light and view through the tester sight. The scale in the refractometer indicates the freeze protection point.

Minimum antifreeze strength should be several degrees lower than the lowest possible temperature for the climate of the area. For example, if the lowest normal temperature for the area is 10F, the antifreeze should test to -20F. A 50/50 mixture of antifreeze and water is commonly used to provide protection for most weather conditions.

NOTE Vehicles, using an aluminum cooling system and engine parts, can be corroded by some types of antifreeze. Use only antifreeze designed for aluminum components. Check the vehicles service manual or antifreeze label for details.

COOLING SYSTEM TESTS

It is often necessary to check the cooling system for cooling system problems. Cooling system problems can be grouped into three general categories:

1. COOLANT LEAKS - crack or rupture, allowing pressure cap action to push coolant out of the system.

2. OVERHEATING - engine operating temperature too high, warning light on, temperature gauge shows hot, or coolant and steam is blowing out the overflow.

3. OVERCOOLING - engine fails to reach full operating temperature, engine performance poor or sluggish.

To diagnose and repair cooling system problems, perform several tests. These tests include the following - cooling system pressure test, combustion leak test, thermostat test, engine fan test, and fan belt test.

Cooling System Pressure Test

A cooling system pressure test is used to locate leaks quickly. Low air pressure is forced into the system, causing coolant to pour or drip from any leak in the system.

A pressure tester is a hand-operated air pump used to pressurize the system for leak detection. Install the pressure tester on the radiator filler neck. Then pump