Water in oil

The pH should be maintained at levels between 7 and 8.5 in engines with soft and harder metals. A pH of below seven is more acidic and aggressive to harder metals, like cast iron or steel, while a pH above 8.5 becomes more alkaline to soft metals such as aluminium, copper and brass. It is therefore important to incorporate a coolant with a pH buffer, such as borate, to regulate the pH in coolant at safe levels. Approved coolant manufacturers offer fully formulated coolants that afford wet liner protection without the need to add extra additives.

Coolant dilution is an absolute must. If coolant concentrations was changed to 70% coolant and 30% water, the heat-transfer value would go up while corrosion protection will drop drastically.

Coolant tends to become acidic over time. That. combined with cavatation in the block, and to some extent, dirt and rust particles in he cooling system, they're proned to electrolysis (also known as wet-sleeve pitting) The cylinder sleeves can end up with small pin holes that let all the coolant drain into the crankcase.