Corrosion
Corrosion loosens solid particles from the surfaces of the cooling system. The particulate enters between the sliding ring seal of the water pump. The abrasive wear causes the sliding ring seal to leak. Corrosion on the inside surfaces of the water pump indicates that the cooling liquid in use provides insufficient corrosion protection.
Causes of corrosion:
- Incorrect, corrosive, ageing or unsuitable cooling liquid.
- Use of water as cooling liquid (without the addition of any coolant agent).
- Leaking cylinder head gasket: Aggressive combustion gases such as carbon dioxide (CO2) and sulphur compounds (H2SO3) enter into the cooling system and lead to the acidification of the cooling liquid and the breakdown of the corrosioninhibiting substances.
- Reduction of the corrosion protection effect of the cooling liquid caused by mixing coolant agents with differing compositions
The alkaline reaction of the cooling liquid leads to normal grey colouring of aluminium parts. However, there must not be any loose deposits (sludge, or dust if dry) on the surfaces that have been coloured grey (finger test). If these are present, this indicates that the cause is material corrosion rather than the alkaline reaction of the coolant agent. The loosened solids generated by this pollute the cooling liquid and lead to abrasive wear on the sliding ring seal.