When to change the fluid in your automatic transmission is something a vague art. A lot of manufacturers will tell you an oil change isn’t necessary until 100,000-150,000 miles, while others will say 30,000. Further confusing the issue, some manufacturer’s like BMW claim to have “lifetime” oil in their transmissions. So when you should change your automatic transmission fluid?
First, let’s look at why you need to change it at all.
What Transmission Fluid Does
Unlike in manual transmissions which, with careful driving, really can go a lifetime without needing new oil, automatic transmission fluid is not merely there to lubricate the inner workings. Automatic transmission fluid doubles up as a hydraulic fluid, like brake fluid. Transmission fluid is pumped into various parts of the transmission in order to engage or disengage certain components.
What Goes Wrong?
Unfortunately, the hydraulic application of clutches is bit of an all-or-nothing affair. If a clutch is fully engaged or fully disengaged, no problem, but if a clutch is partially applied, it will start to wear down, even burn up.
As an automatic transmission is driven a certain amount of wear is unavoidable, and the debris from this wear gets into the oil. This debris can’t be allowed to interfere with the mechanisms, so a filter is fitted. Over time, as the amount of debris increases, the filter will start become clogged up and limit the flow of oil into the system which—yes, you guessed it—can cause clutches to partially apply, reducing their life.
Once the filter is sufficiently blocked the wear process of the frictions is accelerated, further blocking the filter. It’s a viscous cycle.
So How Often Should You Change?
It’s difficult to say. Every 30,000 miles is a good benchmark, but it differs greatly from transmission to transmission. Perhaps more important than the oil change itself is a filter change (though we don’t recommend changing just a filter). Certainly don’t believe any claims of “lifetime” oil, while the oil itself may be fine it’s the debris in the oil that cause problems.
It would certainly be worthwhile to regularly check your transmission fluid—for one thing, running an automatic transmission with an insufficient amount of oil will present all the same problems our blocked filter would—but also because the state of the oil can give you a valuable insight into how your automatic transmission is fairing internally. For example, metallic or black/burnt oil is a clear sign of internal malfunction.
Will Changing the Oil Fix My Automatic Transmission?
In a word, no.
Well, probably not. If the problem is that your automatic transmission is low on oil, then putting more/fresh oil in may very well fix it, but in our experience, once your automatic transmission has started developing noticeable problems, they are either unrelated to the oil, or have progressed beyond the point where an oil change will do the trick.
As a general rule, Dexron III is good for most automatic transmissions, but always check the specifications for your automatic transmission before choosing your transmission fluid! Though certain manufacturers claim their transmissions need their brand of oil to work when in actual fact standard ATF (automatic transmission fluid) will work just fine, some automatic transmissions really do need a certain type of oil.
Further complicating matters, certain transmissions require more than one type of oil, such as the Audi RS6’s ZF5HP24 automatic transmission, which takes ATF in the main transmission, but also requires EP75/90 (gear oil) in two separate compartments, or the DSG DQ200, which takes one type of oil for lubrication and another for hydraulic control.
Is It Worth It
It’s definitely worth staying on top of your automatic transmission’s oil. Proper care and attention may add years onto the life of your gearbox, not to mention saving you a potentially hefty repair bill when your transmission bites the dust!