Automatic gearbox fluid change or flush: what is the difference?

Both treatments give your automatic gearbox fresh fluid. The difference is how much of the old fluid really comes out. That is because an automatic gearbox holds far more fluid than the contents of the sump alone. The sump is the oil pan at the bottom of the gearbox.

A fluid change is the traditional method. The mechanic undoes the drain plug and the fluid runs out of the sump. The mechanic then refills the gearbox with fresh fluid of the specification the manufacturer requires. Where possible, the filter is replaced as well. This is quick, but the torque converter, the oil cooler and the lines do not drain. The torque converter is the fluid coupling between the engine and the automatic gearbox, and it is full of fluid. Part of the old fluid therefore mixes with the new fluid straight away. How much fluid stays behind differs from gearbox to gearbox.

A flush, also called a powerflush, goes further. A flushing machine is connected to the gearbox’s fluid circuit, following the procedure that suits the gearbox type. The machine drains the old fluid and feeds in fresh fluid. This continues until the fluid in the torque converter and the cooler has also largely been replaced. After that come the filter change, if the gearbox has a replaceable filter, and setting the fluid level at the specified temperature.

The table shows at a glance where a fluid change stops and a flush carries on.

How much old fluid stays behind after a fluid change differs per gearbox. Your price depends on the gearbox type and the specified fluid.

Automatic transmission fluid ages and becomes contaminated with wear particles from the clutch plates. According to gearbox manufacturer ZF, fluids age faster at very high operating temperatures. ZF says regular fluid changes mean less wear and less abraded material from the clutch plates, and help the gearbox keep adapting its shifting properly.

Many car makers describe the fluid in the automatic gearbox as a lifetime fill. That does not mean a change is unnecessary. ZF writes in its product information that its automatics are generally filled with lifetime fluid, but still advises replacing the fluid after 150,000 km. With high temperatures and heavy loads, or if it is not known how the car was used before, ZF says it can make sense to change the fluid sooner.

In those cases ZF advises a shorter interval. When your make and gearbox type are due is explained in when to have your automatic gearbox flushed. Also read your manufacturer’s requirements in the service book.

Read both lists. The one that best describes your situation points to the right treatment.

Does the gearbox jerk, slip or shift harshly? Then it needs checking first. Fresh fluid can help if contaminated fluid is the cause. According to the ANWB, the Dutch motoring organisation, a flush is in the best case enough to get the dirt and old fluid out of an automatic gearbox with complaints. If the problem is more serious, the gearbox has to come out so it can be inspected part by part. A complaint can also have an electronic cause. Which signs point to a problem is explained in recognising automatic gearbox problems.

No. The difference between a fluid change and a flush is greatest with an automatic that has a torque converter, because a lot of fluid sits outside the sump. Other gearbox types work differently.

Rule of thumb. We check what your gearbox needs for each car, based on the registration number and the gearbox type.

A DSG and a CVT have their own requirements. You can read the approach for each type on our pages about DSG flushing and CVT flushing.

We start with the question of what your automatic gearbox needs. Advising a flush where a fluid change is enough does not help you. The same applies the other way round. This is how it works in our workshop:

1. Intake: we look at your registration number, the gearbox type and the service history, and discuss any complaints.
2. Test drive and reading the fault memory: we take the car for a short test drive and, where possible, read the transmission control unit for stored fault codes.
3. Advice and quote: you hear whether a fluid change or a flush suits the car, and what it costs. We only start once you have agreed.
4. Fluid change or flush: we use fluid with the specification the manufacturer requires. If a cleaning agent is permitted for your gearbox, we use it according to the requirements.
5. Filter: if the gearbox has a replaceable filter and this falls within the job, we replace the filter and the seal. On some gearboxes the filter is built into the sump pan, and a new pan is needed.
6. Fluid level and check: we check the fluid level with the car level and at the specified temperature, following the gearbox manufacturer’s procedure, and finish with a test drive.
7. Old fluid: we dispose of the old fluid in line with the environmental rules for garages.

A flush usually takes two to three hours. You can often collect your car the same day. You can read more about the treatment on our page about automatic gearbox flushing.

A fluid change costs less than a flush. Less fluid goes in and the work is done sooner. A flush needs more fluid and more time, but it also replaces the fluid in the torque converter and the cooler.

What you pay depends mainly on your gearbox type. The gearbox type determines how many litres of fluid are needed, which specification the manufacturer requires and whether the filter or the sump pan needs replacing. You can find guide prices per make and gearbox type on our page about the cost of an automatic gearbox flush. For your own car you receive a quote in advance. Call us with your registration number on +31 10 479 00 00.

A flush is the most complete treatment, because the fluid in the torque converter and the cooler is also largely replaced. A fluid change is not pointless. For a well-maintained gearbox without complaints it works well as routine maintenance. After years without maintenance or with an unknown history, a flush is usually the better choice.

An automatic gearbox holds more fluid than the contents of the sump alone. The torque converter, the oil cooler and the lines are also full of fluid and do not empty when the gearbox is drained. As a result, part of the old fluid stays in, however carefully it is drained.

The treatment itself should not damage the gearbox if it is carried out according to the requirements. It can, however, become clear after the flush that the gearbox was already mechanically worn. That is why we take the car for a test drive and read the transmission first. You can read more in problems after a gearbox flush.

With a flush, we replace the filter as standard if your gearbox has a replaceable filter. On some gearboxes the filter is built into the sump pan, and a new pan is needed. It is also possible with a fluid change, but then the sump has to come off. The filter is included in the quote, so you know the cost in advance.

Yes. Lifetime does not mean a change is unnecessary. Gearbox manufacturer ZF advises changing the fluid in its automatics after 150,000 km, and sooner with heavy loads or an unknown history. Also read your manufacturer’s requirements.

Only fluid with the specification required by the maker of your car or gearbox. An automatic gearbox is sensitive to the wrong fluid. We look up the right specification using your registration number and the gearbox type.

A fluid change is done sooner than a flush. A flush usually takes two to three hours, including the test drive, filling and the final check. You can often collect your car the same day. You can wait nearby or, as long as one is available, use our free loan bike.

Yes. We can combine the fluid change or flush of your automatic gearbox with a car service. Then everything is done in one visit. Call +31 10 479 00 00 to make an appointment.

• ZF Aftermarket: ZF LifeguardFluid 8 product information (transmission fluid, fluid change after 150,000 km)
• ZF Aftermarket: InBrief: ZF oil change kits
• ANWB: 5x dure autoreparaties bij occasions, section on the gearbox (in Dutch)
• ANWB: Versnellingsbak uitgelegd, torque converter (in Dutch)