What Is Inverter Coolant?

An inverter is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC) at a given voltage and frequency. Inverters are used in many applications that range from speed controllers of electric motors to UPS.

In a vehicle, the electric motor converts the DC produced by the car’s batteries to AC so that the car can run. Inverters aren’t entirely efficient and some of the power produced gets wasted as heat. Therefore, a cooling system is required to cool this system. Inverter coolant cools the device that converts DC power to AC power used to run the electric motor.

Inverter coolant vs engine coolant

There’s a great deal of energy produced by a car engine as it burns petrol or diesel. Around one-third of the energy produced is used in moving the car forward, whereas the other two-thirds is converted into heat. Half of the heat converted is emitted out through the car’s exhaust while the other half remains inside the engine block.

Because of this heat, car engines have to be cooled down. If a car engine didn’t have a cooling mechanism, then the increase in temperature would cause the working metal components of the engine to start melting or fuse.

This will eventually cause your engine to seize functioning. To absorb the heat from the engine, a water-based liquid referred to as an engine coolant is used.

As the engine coolant absorbs the heat from the engine, it becomes hot itself and is transferred to the car’s radiator. The hot coolant passes through the veins found in the car’s radiator and is cooled by cold air as the car moves forward. A fan in the car helps to maintain airflow through the veins if the car remains stationary for a long period.

Engine coolant is used to ensure that the engine is always at an optimum temperature. This helps to prevent any engine failure due to cooling problems. Engine coolant is a mixture of water and antifreeze. It comes in a variety of colors that include orange, yellow, pink, or green.

The car uses the same coolant for the engine and the inverter. Similar to engines, inverters also produce heat that may otherwise cause damage to the electric motor if a certain temperature isn’t maintained. Inverter coolant helps in keeping the system at a proper operating temperature.

Even though the same liquid is used in cooling the engine and the inverter, the two have separate cooling systems. If you have a liter of coolant, the engine system takes 0.64 liters whereas the inverter system takes 0.36 liters.

The inverter system may develop bubbles and may need to be properly bled. Failure to do so may otherwise burn out your car’s inverter. A burnt-out inverter is quite expensive to replace and may amount to “junking” the car.

Prius inverter coolant

The maintenance manual of most Toyota Prius vehicles recommends that the inverter coolant is changed at 15,000 miles or after 18-months of use. This means that you need to check that there’s enough coolant in the reservoirs and change it if the need arises.

Most Toyota dealers would advise you to change the inverter coolant of your Prius at 15,000 miles but according to online discussions, coolants can last up to 100,000 miles before they require replacement.

You can also check the color of the coolant fluid every year to see if it’s still pink and that the pH is still within the specs. You can also use a digital voltmeter to check your Prius inverter coolant. To do this you put the negative probe of the voltmeter on the negative post of the car battery and then the positive probe on the radiator’s neck.

A voltage of 0.2 to 0.5 means that your coolant is okay whereas voltage ranging from 0.5 to 0.7 means that it’s on the borderline. If the voltmeter returns a voltage of 0.7 and above, then your coolant will need to be replaced.

The 2001-2003 Prius uses Long Life Coolant (LLC) in both the engine and inverter coolant system. IIRC coolant needs to be diluted with at least 50% of deionized water. Practically, it’s possible to transfer the coolant from one system to another using turkey baster depending on your preference.

For 2004 and newer Prius models, the Super Long-Life Coolant (SLLC) is used and comes already 50% diluted. The SLLC is backward-compatible and has a longer specified change interval (50,000 to 30,000 miles). You may have to consider using newer coolant when you need replacement.

The LLC and SLLC are the only known coolants that are acceptable for use on the Prius. Prius coolant may come in either red or pink color. You can look for radiator shops that accept old coolant if you’re looking to dispose of it responsibly.

Hybrid inverter coolant

Most hybrid vehicles have a separate cooling system for their inverters and electric motors/generators. The cooling systems usually have special coolants, heat exchangers, and an electric pump. The Prius has two coolant reservoirs under the hood. It’s important to always make sure that the coolant fluid is at the correct level.

As most manufacturers will recommend, it’s important to empty the coolant reservoir and fill it with new coolant when the engine’s cooling system is being serviced. The Prius is a hybrid vehicle and as such the hybrid inverter coolant used will be similar for the same type of vehicles.


A car’s inverter converts DC to AC using an electric motor. The heat produced during this process can cause damage to your car’s electrics if your cooling system doesn’t work. The engine and inverter use the same coolant which is a mixture of water and antifreeze. However, the engine and inverter have separate systems that help keep the engine and inverter operating at an optimum temperature.

The Prius is a hybrid vehicle that uses LLC and SLLC coolant for their invertors. The coolant level and color must be constantly checked to ensure that it can function properly. Digital voltmeters can be used to confirm this. Manufacturers recommend that the inverter coolant in the Prius is replaced after 100k miles. 

About The Author