What oils and fluids does an electric car need?

The most convincing people on the subject of electric cars are used-car sellers: “There’s nothing to change here: no oil, no filters, no belts. Charge it and drive.” They never lack an audience. In 2025 around 110,000 electric cars were added to Ukraine’s roads — twice as many as the year before, and roughly one imported car in four was electric: buyers were hurrying to make use of the VAT exemption on imports, which ran until the end of 2025. So a great many car owners are now asking “what is there to change in it anyway?”

An electric car really has no engine oil — there is no engine to need it. (If you drive a hybrid, that is a different story altogether: there is an engine, and the oil in it works in very difficult conditions; that has an article of its own — the hybrid and its oil.) But “no engine oil” by no means equals “no oils or fluids”. The reduction gearbox, the battery, the brakes and the air conditioning each have their own, and each is matched to that particular design. I will say it once more: fill it with what the car manufacturer specified, and for an electric car that rule is even stricter than for an ordinary one.

The reduction gearbox and e-fluids

As a rule, an electric car has no gearbox in the usual sense: the electric motor spins across a very wide rev range, and between it and the wheels there is a reduction gearbox — a gear pair or two and a differential. Gears need lubricating, so there is oil in there. Put simply, the oil in an electric car’s reduction gearbox is gear oil that, on top of everything, has to work right next to electrics.

The point is that in modern designs (they are called an electric axle, or e-axle) the motor, the gearbox and the electronics sit in one housing, and the oil often washes over the motor windings. So it is asked to do things nobody ever asked of an ordinary gear oil:

1. Not conduct current. The oil must be a good insulator, otherwise the windings risk a breakdown.

2. Not eat copper. The windings are copper, and the additives of many ordinary gear oils contain active sulphur, which copper does not survive for long.

3. Carry heat away. This oil also cools the motor, so it has to draw heat away from it well.

The oil in such a gearbox works rather like the insulation of the wiring in your flat: as long as it is intact, nobody gives it a thought, and once it stops insulating, everybody thinks of it at once. That is exactly why car manufacturers specify a particular fluid for their gearboxes: in newer designs, more and more often a dedicated e-fluid, and in some models a particular ATF to their own specification, in which case only that one will do. “ATF” or “75W-90” on the can tells you nothing about whether that oil suits your gearbox: only the car’s documentation can tell you that.

And what about “filled for life”? For some models that is exactly what it says: the manufacturer schedules no oil change for the gearbox. For others the service book gives a change interval, just as for an ordinary transmission. “Filled for life” only means “no scheduled change”, not “for ever”: electric cars leak too, and after a gearbox repair it will have to be refilled anyway — and only with what the documentation specifies.

Battery cooling

A battery likes neither heat nor frost, so many electric cars have a liquid cooling circuit of its own for it (and for the motor and electronics while it is at it); some models, admittedly, cool the battery with air alone. It looks like the same system as on an ordinary engine, but the requirements are different. Coolant makers already produce separate fluids for electric cars, with reduced electrical conductivity: if such a fluid comes into contact with high voltage, it must not conduct current or break down and give off hydrogen.

Still, here too it is the car manufacturer who has the last word. An example from its own documents: for the electric Audi e-tron the manufacturer approves only one coolant, G12evo (the same as for ordinary Audis), and no other.

Colour means nothing here, just as in an ordinary car: the colour of a coolant is only a dye, not its chemistry. So a “universal” antifreeze that, according to its label, “suits all makes” is a lottery in an electric car, and the stake is the battery. What additive packages there are and why they must not be mixed is covered in the article on modern antifreezes.

Brake fluid

An electric car does most of its braking with the electric motor: the energy goes back into the battery, and the pads and discs work far less. Hence another piece of “helpful” advice: the brakes hardly work, so there is no need to change the fluid either. Wrong: brake fluid ages not from work but from time. It absorbs moisture from the air, and the more water it holds, the lower its boiling point. The American standard FMVSS 116, to which the DOT marking refers, sets two minimum boiling points for good reason: one for fresh fluid and one for “wet” fluid. So it is changed by the time given in the service book, however much (or however little) you have braked. What exactly to fill it with and why some cans say “LV” is covered in the article on DOT 4 LV brake fluid.

Air conditioning

The air-conditioning compressor’s oil is remembered only when the system is being recharged, if then, and that is a mistake. In an electric car the compressor is driven by its own electric motor, so its oil must be an insulator too. The usual compressor oil for cars with an internal combustion engine (PAG) will not do: even a small admixture of it spoils the insulation, and some car manufacturers then require the entire air-conditioning system to be replaced. So before the air conditioning is recharged, make sure the technician knows he is dealing with an electric car and fills it with the oil the manufacturer specified.

What to change and when

So here is what in an electric car does need attention after all:

1. Reduction gearbox oil (e-fluid). Per the service book; if it says “no change”, keep an eye out for leaks.

2. Coolant. Only the one the manufacturer specified, and at its interval.

3. Brake fluid. By time, as in any other car.

4. Air-conditioning compressor oil. Only the one the manufacturer specified for this car.

As you can see, “nothing to change” is a seller’s slogan, not an owner’s manual. An electric car has fewer fluids than an ordinary one, but each of them is more demanding, and an “equivalent” can cost even more here; I have already written about that in the article on analogues and substitutes. Check the service book, and if there is none (with an imported used car that happens more often than one would like), ask the brand’s official representative what should be changed and when. And if the car’s history is unknown, it is wiser to change the brake fluid straight away rather than wait.

Further reading:

• What are “original” service fluids?
• Why should you change all the fluids regularly, not just the oil?