Why does the engine heat up so fast with full coolant-water at about 50 mix?

It is not true that an engine would heat up faster with a 50% coolant-water mix. In fact, a 50% coolant-water mix is typically used in cars to regulate and maintain optimal engine temperatures. Coolant, usually containing ethylene glycol or propylene glycol, plays a vital role in preventing a car’s engine from overheating.

Coolant increases the boiling point of the water-coolant mixture and also lowers its freezing point, ensuring the engine operates within a consistent temperature range regardless of harsh weather conditions.

Using pure water instead of a coolant-water mix can indeed lead to faster engine heating due to water’s lower boiling point compared to coolant. Water alone would have a risk of vaporizing and forming pockets of steam within the engine, causing hotspots and potentially leading to severe damage.