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Volvo Bus Service and Maintenance Manual

 Cooling system and heater maintenance
27 During the winter, check the coolant anti-freeze protection. If necessary, adjust the glycol/water mix to provide protection in accordance with local conditions, see below.
28 Pressure-test the cooling system. Inspect all hoses for hardness, cracks, separation, etc. Inspect the heater system for leaks. Replace parts if necessary.
29 Drain the coolant and flush the cooling system. Change any coolant filter at the same time as the coolant. Fill the system with a new coolant mixture of glycol and water, 50/ 50. The table below shows the mixing percentage at the various temperatures.

WARNING! Anti-freeze (glycol) is poisonous.

Glycol (anti-freeze)40%45%55%60%
down to-13°F-23°F-40°F-69°F

Note: The glycol concentration must be between 40% and 60%. Lower than 40% will not provide sufficient protection against rust, in some cases the rusting may even increase. Never mix different coolant types. The anti-freeze protects the cooling system from damage due to freezing and rust. If anti-freeze is not required, Volvo recommends coolant rustproofing additive no. 1129 709-0, in a mixture of 0.5 litre to 14 litres of water. After every 20,000 km or 400 hours of operation, the rustproofing protection should be reinforced with an additional 0.5 litre rustproofing additive for buses with front engines and with 1 litre for rear and mid-engine buses.

The rustproofing additive must not be mixed with antifreeze.

The use of unsuitable rustproofing and anti-freeze fluids can cause foaming and other problems. With foaming there is risk of parts seizing resulting in damage expensive to repair.

The genuine Volvo antifreeze is specified in the Volvo Group Standard.

Pressure-testing the cooling system

If the cooling system has to be frequently topped-up with coolant, it should be pressure-tested. Topping up after filling may indicate air in the system.

Connect pressure tester (999) 6662 and hose (999) 6049 and nipple 998 6346 to the radiator's drain connection. Gradually increase the pressure. The expansion cap's overflow function should start to release pressure at about 50 kPa (0.5 kgf/cm2).

Pressure testing the cooling system

Then connect-up pressure tester 6662 and cap (999) 6441 to the expansion tank and apply a pressure of 70 kPa (0.7 kgf/cm2). If the pressure drops, this indicates leakage. Find out where this is and remedy it.

Cooling system expansion tank