Flushing an automatic gearbox or changing the fluid yourself: can you?

Plenty of people change their own engine oil. An automatic gearbox is a different story. On some gearboxes draining the fluid is still possible, but filling it and checking the level require a set procedure at a set temperature. This article explains what is involved, where the risks lie and what you can safely do yourself.

By the team at Autobedrijf Willemsbrug, RDW-approved APK (MOT) test station since 1979 · Updated 4 November 2026

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The short answer

You cannot flush an automatic gearbox yourself, because it takes a flushing machine that is connected to the gearbox’s fluid circuit. Changing the fluid is technically possible on some gearboxes, but filling and checking the level follow a set procedure. On ZF automatics this is done through a filler hole in the gearbox casing. ZF specifies a fluid temperature of 30 to 35 °C for the 6HP and at most 40 °C for the 8HP, and warns that too much or too little fluid can damage the gearbox. What you can do yourself: keep an eye out for leaks, note down complaints and look up the specified fluid and the service history.

Can you flush an automatic gearbox yourself?

No. A flush, also called a power flush, needs a flushing machine that takes over the fluid circuit of the automatic. The machine removes the old fluid and supplies fresh fluid at the same time, following the procedure that suits the transmission. This way a larger share of the old fluid comes out than with draining alone, including from the torque converter and the cooler. The torque converter is the fluid coupling between the engine and the gearbox.

What is possible is a fluid change: draining the fluid, replacing the filter on some gearboxes and refilling with new fluid. Only the fluid in the sump drains out. The sump is the oil pan at the bottom of the gearbox. The difference between the two treatments is explained in our article on changing or flushing gearbox fluid.

Pouring cleaners or additives into the gearbox is no alternative to a flush. ZF writes that you should not use any supplementary additives or cleaning agents, because they change the chemical composition of the transmission fluid.

What is involved if you change the fluid yourself?

A DIY fluid change takes more than a can of fluid and a drip tray. ZF describes the fluid change on its automatics for workshops in a set order. In short:

  1. Open the drain plug and collect the old fluid.
  2. Replace the filter and its seal, or on some gearboxes the complete plastic oil pan with built-in filter, using new bolts and a new seal for the drain plug.
  3. Tighten everything to the torque settings the car maker specifies.
  4. Open the filler plug and fill with ZF LifeguardFluid until the fluid runs out of the filler hole.
  5. Let the engine idle and move the selector lever to R and D in turn. Then run through the gears following the pattern for your gearbox. On some gearboxes this includes 30 seconds at 2,000 rpm to fill the torque converter.
  6. Check the level once the fluid is at the specified temperature. If no fluid runs out, top up.
  7. Let the engine run until the gearbox reaches 40 °C and only a few drops still come out of the filler hole. Then close the filler plug to the specified torque.

This is a summary of ZF’s method for its own automatics. Other gearboxes have their own procedure. So use the instructions for your own gearbox, and the fluid with the specification that goes with it. Our article on which automatic transmission fluid your car needs explains which fluid that is.

Why is the fluid level the hardest part?

The fluid level is tricky because you can only judge it properly at a set fluid temperature. Fluid expands as it warms up. So in a gearbox that is too cold or too warm, there seems to be more or less fluid than there really is. That is why ZF specifies that the fluid must be between 30 and 35 °C on the 6HP and at most 40 °C on the 8HP before you check the level.

Some modern automatics no longer have a dipstick. On ZF automatics you check the level through the filler hole in the gearbox casing: the level is right when, at the correct temperature, a small trickle of fluid still runs out of the hole. The fluid temperature is not shown on the dashboard. In the workshop we read it with diagnostic equipment while the engine is running. We check the fluid level with the car level and at the specified temperature, following the gearbox manufacturer’s procedure.

According to ZF, too much or too little fluid, or a level check at the wrong temperature, can damage the gearbox. Also do not run the engine or tow the car while there is no fluid in the gearbox.

What are the risks if you do it yourself?

The biggest risk is a gearbox with the wrong fluid or the wrong level. You sometimes only notice that damage later. These are the points that most often go wrong:

  • The wrong fluid: ZF only allows LifeguardFluid 8 or 9 in the 8HP. According to ZF, other fluids can lead to noticeably worse shifting and even gearbox failure.
  • Warranty: Nissan writes that a fluid other than the specified NS3 will damage the CVT, and that this damage is not covered by the warranty. Read your manufacturer’s terms and conditions.
  • Level and temperature: without reading the fluid temperature, the level check is an estimate.
  • Missing the warning signs: if the drained fluid smells burnt or contains chips or metal particles, the gearbox is damaged, according to ZF. If you drain it yourself, such a sign is easy to miss.
  • Working under the car: you work under a car that must be raised high and securely, with hot fluid.

According to TopGear Netherlands (September 2026), repairing or overhauling a broken automatic can easily run into thousands of euros. Weigh that against what you save by changing the fluid yourself.

What can you do yourself for your automatic?

You can do a lot yourself to spot problems early, without working on the gearbox. These points also help the mechanic if the car goes to the workshop later:

  • Keep an eye out for leaks: after the car has stood overnight, check for spots underneath. What the colour tells you is explained in our article on fluid under the car.
  • Note down complaints: write down when the complaint happens. Cold or warm, in which gear, when pulling away or braking, and since when.
  • Look up the specification: check the owner’s manual for the transmission fluid the manufacturer specifies.
  • Check the history: look through invoices and the service book to see whether the gearbox fluid has ever been changed or flushed.
  • Driving style: do you often tow a trailer or caravan, or do a lot of fast or sporty driving? Then ZF advises changing the fluid sooner.

Which signs point to a problem is explained in our article on recognising automatic gearbox problems.

DIY fluid change or a workshop flush: what is the difference?

The difference lies in how much old fluid comes out, how the level is checked and whether anyone assesses the gearbox before and after. The table puts the two side by side.

Item DIY fluid change Workshop flush
Old fluid removed Only the fluid in the sump A larger share, including from the torque converter and the cooler
Fluid temperature during the level check Hard to determine without diagnostic equipment Read electronically, level checked at the specified temperature
Assessment of the gearbox None Intake, test drive and, where possible, reading the fault memory
Filter and seal Order and fit them yourself Replaced if the gearbox has a replaceable filter and this is part of the agreed job
Final step No check afterwards Final test drive

Working method of Autobedrijf Willemsbrug. Level check according to ZF at 30 to 35 °C (6HP) or at most 40 °C (8HP).

Flushing is maintenance, not a repair. It does not fix internal wear, leaks or electronic faults. That is why we start with an intake and a test drive, and only flush when it makes sense. The treatment itself usually takes two to three hours and the car is often ready the same day. According to TopGear Netherlands (September 2026), changing automatic transmission fluid, with a filter if needed, costs € 350 to € 600 on average. For your own car you receive a quote in advance based on your registration number, and we only do extra work once you have agreed. You can read more about the treatment on our page about automatic gearbox flushing.

Frequently asked questions

Can I top up the transmission fluid myself if the level is low?

No. A low level can point to a leak, and the level can only be measured properly at the specified temperature. Have the cause found first. We look for the cause and top up with fluid that meets the specified standard.

Does every automatic have a dipstick?

No. It differs by gearbox. On ZF automatics you do not check the level with a dipstick but through the filler hole in the gearbox casing, at a set fluid temperature. Check the owner’s manual for your car or call us with your registration number.

Is a cleaning agent in the gearbox a good idea before I change the fluid?

No. ZF writes that you should not use any supplementary additives or cleaning agents. In our workshop we only use a cleaner if it is permitted for that particular transmission.

What does changing the fluid myself mean for the warranty?

That depends on your manufacturer’s terms and conditions. Nissan, for example, writes that damage caused by a fluid other than the specified CVT fluid is not covered by the warranty. Read your manufacturer’s terms and keep the receipts for the fluid and parts you use.

Is it wise to change the fluid in a DSG or CVT yourself?

No. We advise against it. These gearboxes also have their own fluid and their own filling and checking procedure. For the CVT, Nissan recommends contacting a dealer or a qualified workshop when the fluid needs checking or replacing.

What do I do with the old transmission fluid?

Take it to the municipal recycling centre, called a milieustraat in Dutch. According to the Dutch waste sorting guide from Milieu Centraal, oil such as lubricating oil belongs there. In Rotterdam the recycling centre is called a milieupark, and oil goes with the chemical waste (chemisch afval). See the City of Rotterdam milieupark page (in Dutch). If you have the fluid changed with us, we dispose of the old fluid in line with the environmental rules for garages.

Would you rather have it done?

Call us with your registration number. We look up your gearbox type and the specified fluid, and you receive a quote in advance.

You will find us at Boterdiep 11 in Rotterdam-IJsselmonde, close to Stadion Feijenoord (De Kuip). We work by appointment. For a quick question or check you can walk in without an appointment.

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