By November 14, 2013 0 Comments Read More →

What is a Transmission Flush?

what is a transmission flushWith all the talk about “flushing fluids” lately, cooling system, fuel system, power steering fluid, brake fluid etc. etc. etc. what the heck is all this flushing about and when or should you do it to begin with?

Well, I am so glad I asked myself that question because I get tons of emails each day involving these issues.

Flushing fluid in your car is not a bad idea, but flushing the automatic transmission fluid is NOT a good ideal if you are having a problem with slipping or jerking.

Let me explain further.

Say you get into your vehicle in the morning and it is slow to reverse out of the garage. The engine revs up, the RPM’s go up but the vehicle is not moving or not moving as quickly as it should with that high of engine RPM. Your automatic transmission is probably slipping, the clutches inside it are rubbing together but there is not enough friction or fluid pressure to make the car move.

This example above can usually get worse as the engine heats up later in the day when the transmission fluid is hotter and thinner in viscosity.  The clutches will have a harder time of producing friction and pressure to move the vehicle.  And just so you know, reverse gear is usually the first gear to show signs of internal transmission wear.

So, in this example if you run out and “flush” or change the transmission fluid with slick new fluid you have removed even more of the friction that the old gritty and dirty fluid had, so you actually make the problem WORSE by flushing or changing the fluid.

If you have any slipping or excessive jerking caused by the transmission, do nothing and talk to a local transmission shop and get them to take a test drive with you for their opinion on what to do.

In most cases you don’t have a choice, continue to drive until it just finally gives out and won’t pull itself at all or bite the bullet and overhaul the transmission now. Sorry :(

Now, if you are NOT experiencing any slipping or jerking issues and just want to keep your transmission in the best shape you can, then yes flushing is a great option now.

I would recommend you flush the transmission fluid every 50,000 miles at the most to keep your automatic transmission in the best condition you can. I would also recommend you change the transmission filter as well, if you have one, some vehicles do not have a replacement filter.

Flushing is easier and safer for the oil change guys to do, there is less chance that they break something removing the transmission pan from the vehicle.

Flushing also removes more of the fluid than removing the transmission pan would allow you to do. So there is a trade off here, remove more of the oil fluid and keep the old filter in place, or replace the filter and leave some of the old fluid inside the transmission.

If your vehicle does not have a replaceable transmission filter, go ahead and flush.

If your vehicle has been in high water and water is inside the transmission fluid, flush it

If your vehicle has had another fluid added and contaminated your fluid (you put motor oil in trans) flush it

If your vehicle has a serviceable transmission filter, and no other issues present maybe you would want to replace the filter as well as the fluid.

I also recommend you use a quality name brand fluid and the PROPER fluid type for your vehicle. There are a few types of transmission fluids, so read your manual and make sure you use the type designed for your vehicle.

Using a newer synthetic fluid (compared to the old conventional fluid) is a great idea, but costs more so you will have to weigh your costs versus any possible extended life span it MIGHT offer.

Using a transmission fluid additive like from lucas oil is a great idea as well after a flush or service.

I hope this helps you,


Austin Davis



Posted in: Transmissions

About the Author:

Austin Davis, consumer car repair advocate. "Hi there! I love to help people solve their car repair problems and I hope my site was helpful to you today. Thank you for stopping by."