Media post: Change Intervals for Functional Fluids

There are several systems in your car that use oil-based fluids for “functional purposes.” This means the fluids are a part of a particular system and perform things like hydraulic movement and lubrication. A non-functional fluid would be something like the cleaning fluid in your windshield washer system. In this article, we will look at the manufacturer’s recommended change intervals for the three most common functional fluids.

Automatic Transmission Fluid
The suggested change interval for today’s automatic transmission fluid is 60,000-100,000 miles. In the past, some manufacturers suggested that the fluid would be replaced only when a change in transmission shifting occurred. Today, modern transmissions are “smarter” and can mask worn and depleted transmission fluid by changing shift points automatically. However, it is still possible for transmission fluid to wear out, you just can’t feel it when the transmission shifts anymore. What happens is that the original fluid’s viscosity changes and gets dirty, issues that can damage the clutches and bands. This can damage an automatic so it is smart to change both your transmission’s filter and fluid according to the manufacturer’s suggested schedule.

Power Steering Fluid
The suggested change interval for today’s power steering fluids is 60,000-80,000 miles. Not long ago, there was no definitive change interval for power steering fluid because it really didn’t get dirty and worn out. Things are different today. Wider wheel and tire packages are putting more strain on power steering systems and this means more heat is generated. If it gets hot enough, the heat can degrade the fluid and eventually damage the seals in the pump and rack. Hence, most manufacturers now have recommended change intervals for their power steering systems.

A note for do it yourselfers: Our subject matter experts for this article, King Buick Chevrolet GMC in Longmont, CO, remind us that there’s an old saying: There is no such thing as a universal fluid. Different manufacturers use formulations for their power steering, transmission and brake systems that are matched to the type of seals they have installed in the system. If you add the wrong fluid to your car’s automatic transmission, for example, you may end up ruining the transmission seals. So, make sure that before you add any fluids to your car, check your driver’s manual for the correct fluid type, or with your local brand dealer for their recommendation.

Brake Fluid
The suggested change interval for today’s brake fluids varies from every 100,000 miles to 150,000 miles. The specific time depends on the manufacturer, of course. Some old timers will find this odd because in the old days, brake fluid was rarely changed. Today, systems like ABS have become standard on most vehicles and these can be hard on the car’s brake fluid. The high pressure and force exerted on the fluid can degrade the fluid and additive packages.