2021 Toyota Highlander Coolant Capacity, Type & Flush Guide

The 2021 Toyota Highlander holds between 7.7 and 10.4 quarts of coolant depending on the engine type and equipped towing packages. As an ASE-certified master technician, I regularly service these family haulers, and ensuring you have the correct coolant chemistry and capacity is critical to keeping the Highlander’s engine and hybrid inverter (if equipped) running at optimal temperatures.

Quick answer

• Total Cooling System Capacity: 9.8 to 10.4 quarts (3.5L V6) or 7.7 quarts (2.5L Hybrid engine) plus 2.6 quarts (Hybrid inverter).
• OEM Coolant Spec: Toyota Super Long Life Coolant (SLLC). This is a Pink, Phosphated Organic Acid Technology (P-OAT) coolant.
• Mix Ratio: 50/50 pre-mixed with deionized water (do not add water to the pre-mix).

Capacity by engine option

The 2021 Toyota Highlander is available with a traditional V6 or an ultra-efficient 4-cylinder Hybrid powertrain. Note that the Hybrid model has two separate cooling systems: one for the internal combustion engine and one for the high-voltage inverter.

Note: Capacities are approximate and represent a completely dry system. A standard drain and fill will require slightly less fluid.

Flush interval

Toyota’s Super Long Life Coolant (Pink) is remarkably robust, but it doesn't last forever. The depletion of protective additives dictates when you need to perform a drain and fill.

• Normal Duty: The factory maintenance schedule dictates the first replacement at 100,000 miles or 120 months (10 years), whichever comes first. After the initial replacement, you should change it every 50,000 miles or 60 months (5 years).
• Severe Duty: If you regularly tow heavy loads, drive in extreme stop-and-go traffic in desert climates, or idle for extended periods, I highly recommend stepping up the initial service to 75,000 miles to prevent premature water pump wear.

How to refill & bleed

Air pockets in the cooling system can cause localized overheating or erratic heater performance. Toyota's modern engines require a specific procedure to ensure all air is purged.

1. Drain: With the engine completely cold, place a drain pan under the radiator and open the plastic petcock valve at the bottom. Also, drain the reservoir.
2. Refill: Close the petcock. Slowly pour Toyota SLLC 50/50 pre-mix into the radiator neck until it reaches the base of the filler neck. Fill the reservoir to the "FULL" line.
3. Burping/Bleeding: Leave the radiator cap off (or use a spill-free funnel attached to the neck). Start the engine and turn the cabin heater to maximum heat and the fan on low.
4. Warm Up: Let the engine idle until it reaches operating temperature and the thermostat opens (you will feel the upper radiator hose get hot). You will see bubbles escaping from the funnel/radiator neck.
5. Top Off: As the level drops, continue adding coolant. Once the bubbling stops and the level remains steady, turn off the engine, remove the funnel, and install the radiator cap securely.
6. Hybrid Note: The hybrid inverter cooling system has its own reservoir and requires a scan tool to command the electric water pump on for a proper bleed. I strongly recommend using a vacuum-fill tool for both the engine and inverter systems on the Hybrid to completely avoid trapped air.

Common cooling system issues

The 2021 Highlander is part of the fourth generation (XU70), which has proven to be highly reliable. However, as these vehicles accumulate mileage, a few minor cooling system behaviors should be monitored:

• Water Pump Weepage: The 3.5L V6 engine (2GR-FKS) can occasionally exhibit a slight pink crust buildup around the water pump weep hole. While a tiny amount of dry crust is considered normal by Toyota, active dripping or heavy accumulation means the water pump seal is failing and requires replacement.
• Thermostat Housing Leaks: The plastic thermostat housing can become brittle over time and many heat cycles, eventually leading to hairline cracks and slow coolant loss.
• Inverter Pump Failure (Hybrid): On high-mileage hybrids, the electric inverter water pump can fail. If this happens, a warning message will display on the dash, and the hybrid system will limit power to protect the inverter from overheating.

If you are uncomfortable tackling a coolant flush or diagnosing a leak yourself, don't risk overheating your engine. Find a trusted shop on Repairius.