Requirements made of engine coolant

Pure water is unsuitable as a coolant not just because of the lack of antifreeze properties. Good functioning of the cooling system is only guaranteed once a suitable antifreeze and anti-corrosion agent, or antifreeze for short, has been added.

The BMW vehicle cooling systems may only be filled with appropriately released frost and corrosion protection media. The filling and maintenance rule to be found in the Repair Instructions and operating instructions must be observed.

Antifreeze agents must meet the following requirements:

• They must guarantee operability of the cooling system in winter (anti-freezing protection by lowering the freezing point) and in summer (prevent boiling and boiling over of the coolant).
• The metal parts that come into contact with the coolant (gray cast iron, steel, aluminum alloy, brass, copper and solder) must be protect against corrosion and cavitation.
• They must be neutral with respect to rubber components and plastic components in the coolant circuit.
• They must guarantee the consistency of the above-mentioned quality criteria.

To create these coolant properties, the antifreeze and anti-corrosion agents must be mixed to the correct ratio with water.

Prescribed mixture for coolant: 

50 % antifreeze for antifreeze protection up to -40°C 

The original coolant mixture for the initial filling at the factory has this antifreeze-to-water ratio.

If the proportion of antifreeze is less than 40 % to -29°C (i.e. the water content is higher than 60 %), not only the degree of protection against freezing, but also corrosion protection is reduced. When the water content is too high, this can lead to premature excess temperature in very hot weather or hot climates and as a consequence lead to coolant being ejected out of the system and damage to the engine through excess temperature.

This means that it is essential that an antifreeze and anti-corrosion agent is added even in the tropics.

***** concentration over 55% to -47°C leads to worsening of the cooling properties (heat transfer), the frost protection changes to the opposite direction, i.e. it worsens even more.

The amounts of antifreeze required for protection against freezing are stated (percentage values) on the containers.

Minimum requirements for water quality: 

• Appearance: colorless, clear
• Sediment, without suspended matter
• pH value: 6.5-8.0
• Total hardness, max.: 20° dH (German hardness grade) or in new unit of measurement:
• Total hardness, max.: 3.6 mmol Ca²⁺ /ltr.
• Chloride content: max. 100 mg/ltr.
• Sulfate content: max. 100 mg/ltr.

Tap water with drinking water quality usually fulfills these requirements. Local water utilities can provide information about the quality of the water they supply. If necessary, the water must be treated (e.g. softened) or distilled water must be used.

The quality of regenerated sea water (as found in the Gulf States) is inadequate!