Transmission Fluid 'Flush': What Is It And When Do You Need It?

If you take your car for a transmission service, you might hear or see something about a transmission fluid 'flush'. Many people assume that this refers to the transmission fluid change but it's not. The transmission fluid flush is a separate and different service altogether. In this article, discover what a transmission fluid flush is and when you need it.

What is a transmission fluid flush?

A transmission fluid flush is a service carried out on transmission units to completely remove (flush out) every trace of the old transmission fluid. This service is carried out after a normal transmission fluid drain has been carried out. Once it's done, the oil pan is cleaned, put back in place and a fresh batch of transmission fluid added. In a way, the transmission fluid flush can be referred to or thought of as a more thorough oil change process.  

How is it different from a standard fluid change?

A transmission fluid flush is different from a standard fluid change. This is because a fluid flush is undertaken at different times and for different reasons. But the main difference is that while the fluid change is part of a normal service and seeks to just change the oil, a fluid flush is not part of a normal service and it seeks to do more than change the oil. It seeks to remove every trace of the old oil stuck inside the transmission unit.  

How is it carried out?

A fluid flush is carried out in an auto shop. First, the transmission oil pan is opened and the old oil drained out. The oil is then inspected before being disposed. Next, the cooling duct connecting the transmission unit is disconnected from the radiator and instead connected to a separate fluid dispenser. The engine is then started and the transmission activated while the dispenser continuously runs fluid through the unit. By doing this, the fluid essentially cleans (flushes) the unit and removes all the old oil from every nook inside the transmission.  

When is it needed?

A transmission fluid flush service is only carried out when there is need to undertake one. And that is when the old transmission fluid has been examined and has been discovered to be extremely dirty or to have traces of worn metal shavings. When any of these two situations are noted, a fluid flush is carried out in order to ensure that the new oil will not be contaminated by traces the old one inside the unit.  

If your transmission unit is well serviced and is not damaged in any way, a fluid flush service is not necessary. However, if the old oil from the unit shows signs of wear or contamination, a flush service could go a long way in protecting your transmission from heating issues.