Why does the engine sound louder after changing the coolant?

[StKeegan]

Replacing the coolant is generally unrelated to the engine. If you genuinely perceive an increase in noise, first check whether it originates from inside the engine or from external components such as the belt, alternator, water pump, or tensioner. Typically, start by ruling out external noise sources. How to choose coolant: The fundamental indicators of coolant are its freezing and boiling points. Market-available coolants come in various freezing points like -15°C, -25°C, -30°C, and -40°C. It's advisable to select a coolant with a freezing point at least 10°C lower than the lowest temperature in your region. Coolant replacement cycle: Vehicle coolant generally needs replacement every 2 years or 40,000 kilometers. This is merely a reference interval. For commercial vehicles with higher mileage, the replacement cycle should be shorter. Since driving conditions vary for each vehicle, the replacement should be based on actual usage. Monitor the coolant's condition—if levels are low, replenish promptly. If suspended particles, sediment, discoloration, or deterioration are observed, replace the coolant immediately and flush the system.