Why does the Highlander have two coolant reservoirs?

[IrisDella]

The Highlander uses an independent cooling system for the intercooler, which is why this model has two coolant reservoirs. How to choose coolant: The basic indicators of coolant are freezing point and boiling point. Coolants on the market come with freezing points of -15°C, -25°C, -30°C, -40°C, etc. Generally, you should choose one that is at least 10°C lower than the minimum temperature in your region. How to check if coolant is insufficient: Observe the coolant warning light on the dashboard. If it lights up, it is likely due to insufficient coolant, though it could also be caused by excessively high cylinder temperature. Check the coolant reservoir. If the fluid level is below the minimum mark (MIN), do not continue driving and add coolant promptly. Check the water level markings on the coolant reservoir. The normal coolant level should be between the maximum and minimum marks. To determine if coolant is insufficient, observe the markings. If the coolant level is below the minimum mark, it indicates insufficient coolant.

[LeAmy]

As a long-time Highlander owner with several years of driving experience, I remember being puzzled by the dual coolant reservoirs when I first got the car. Later, I learned that one is the main reservoir directly connected to the engine radiator for cooling, while the smaller one serves as an overflow tank or expansion tank. During operation, temperature fluctuations cause coolant to expand when hot - the small reservoir stores this excess fluid to prevent leaks or boiling. When cooled, the fluid returns to maintain system stability. This design prevents overheating during long drives due to fluid level fluctuations. I always check both reservoir levels during routine inspections, topping up antifreeze if low. During maintenance, I remind mechanics to inspect reservoir hoses to prevent aging damage - it's genuinely practical.

[BennettFitz]

From the perspective of automotive structure, the Highlander's dual coolant reservoirs are designed to optimize cooling efficiency. The large reservoir is the main tank, connected to the radiator to cool the engine; the small reservoir is the auxiliary tank, serving as an expansion compensation unit. When the vehicle accelerates or operates at high temperatures, the coolant expands and flows into the auxiliary reservoir for storage. It automatically returns when temperatures drop, preventing excessive pressure that could damage connections or create air bubbles. This design reduces system failure rates, making it particularly suitable for SUVs operating in variable road conditions, such as uphill driving where engine load is high—the auxiliary reservoir can quickly respond to temperature fluctuations. Regularly check the reservoir seals while driving, and repair any wear immediately to prevent minor issues from escalating.

[McEmilio]

If you're a new Highlander owner, maintaining the dual coolant reservoirs is simple: the large reservoir cools the engine, while the small one stores backup fluid to accommodate thermal expansion and contraction. This design extends component lifespan and prevents sudden fluid level drops that could cause malfunctions. Just glance at the fluid levels within the standard range before and after daily drives—top up with coolant if it falls below the minimum. Make it a habit to inspect pipe connections once a year for effortless peace of mind.