Hi Epul Ejam Snyz, thank you for your question. Regarding a decrease in coolant levels after a long drive, like from KL to Pahang and back, could be due to several reasons:

1. Coolant Evaporation

If your radiator cap is old or faulty, it may not seal properly, allowing coolant to evaporate due to heat and pressure during long drives.

2. Small Leak in the System

Tiny leaks in hoses, the radiator, water pump, or other cooling system components may not show up immediately but could lead to gradual coolant loss, especially under the higher pressures and temperatures of long drives.

3. Overheating

If the engine overheated during the journey, some coolant might have boiled off. This could happen if the cooling system isn’t functioning optimally (e.g., a failing thermostat or radiator fan).

4. Expansion and Overflow

During long drives, coolant expands due to heat. If the overflow reservoir or its cap is not functioning correctly, coolant may escape when it expands.

5. Internal Coolant Leak

In some cases, coolant might leak into the engine through a damaged head gasket, which could lead to coolant loss without visible external leaks. Look for signs like white smoke from the exhaust or milky oil on the dipstick.

6. Air Pockets in the System

If the cooling system wasn’t properly bled after a coolant change, air pockets could cause an uneven flow of coolant, leading to fluct