Is it okay to mix old and new coolant?

It is not recommended to mix old and new coolants, as coolants of different brands or models vary significantly in chemical composition, additive formulas, and performance indicators. When coolant needs to be topped up, priority should be given to products of the same specification as the original factory ones, and the liquid level should be maintained between the MIN and MAX marks on the reservoir when the engine is cool. In emergency situations, distilled water can be temporarily added (only for organic acid-type coolants), but the coolant should be completely replaced with new fluid as soon as possible to ensure system stability. Regularly checking the coolant condition and performing a complete replacement according to the interval recommended in the vehicle manual (typically every 2 years or 40,000 kilometres) is a key measure for maintaining engine health.