Back in the 1970s and early 1980s, it was not unusual to hear people ‘who know about cars’ say, ‘You can use transmission fluid as power steering fluid. They are basically the same thing!’ And they were right, up to a point.

In the 1970s, lots of American made cars, especially Fords, could use ATF in place of power steering fluid and it would work just fine. It wouldn’t damage the power steering system because they are both essentially the same thing. They are hydraulic fluids.

Back then, as long as the owner’s manual didn’t specifically warn against mixing the two.

For Short Term Use Only

Even back in the 1970s, it wasn’t a good idea to use transmission fluid in your car’s power steering system on a long term basis. Using ATF in power steering systems in cars made in the United States was okay in an emergency.

However, using large amounts of it in the steering system for a long period of time could damage the seals and other parts of the system. The power steering systems of cars that were produced in the 1970s were made using crude materials. They were tougher than the power steering parts in the more sophisticated systems found in the cars today.

Similar But Not Identical

Transmission fluid and power steering fluid are similar, but not identical. Both are hydraulic fluids, but they also contain other additives unique to each type.

ATF contains detergents as well as friction modifiers. PS fluid, on the other hand, typically adds lots of extra lubricants

So, while the friction modifiers may serve a similar purpose as the lubricants, they are not the same thing. They don’t have the oils that are found in power steering fluid that help rubber valves to expand. Instead, transmission fluid causes the rubber seals to deteriorate and develop leaks over a long period of time.

They Perform Different Functions

The detergents and friction modifiers in transmission fluid are designed to perform different functions than those in power steering fluid. They break down and filter dirt and grease, preventing these nasties from damaging key parts of the power steering system.

Power steering fluid is designed to reduce excessive temperature build up and prevent friction among the power steering system parts. It also gives the steering system hydraulic pressure and lubricates both the gear unit and the steering pump.

Specialized, Sophisticated, Lightweight, Delicate Parts

It’s not a good idea to use automatic transmission fluid in place of power steering in most makes and models of modern automobiles. Modern power steering systems are made with more specialized, sophisticated materials; they are more subtly engineered. For them to function properly, they require products that are specifically designed for them. Pouring ATF into the power steering system of today’s technologically advanced cars is a recipe for disaster. It could end up an expensive nightmare or even break it completely.

Never Use ATF In Most Foreign Car Power Steering Systems

It may be possible to use a small amount of transmission fluid in steering systems of certain Ford and GM models. However, adding automatic transmission fluid to the power steering systems of Audis, BMWs, Hondas and Mercedes Benzs is not recommended.

If you use transmission fluid in the power steering systems of these foreign makes and models, it will not meet their specific requirements. Doing so could be harmful. As far as most foreign vehicles are concerned, using transmission fluid in place of power steering fluid is not even a consideration.

Toyota Recommends Dextron III ATF For The Power Steering System

Most foreign made automobiles warn buyers not to use automatic transmission fluid in their power steering systems. Toyota is different.

In fact the Japanese automaker actually recommends it. Owners of Toyota cars can definitely use automatic transmission fluid to fill up the power steering fluid reservoir. The automaker tells buyers that Dexron III automatic transmission fluid is ideal for this use.

Many knowledgeable automotive service and repair experts say the power steering fluid that comes in Toyotas look different than Dexron III. This is simply because Toyota uses undyed transmission fluid as power steering fluid.

Using ATF For Nissan Power Steering Fluid

I asked my mechanic, “can I use transmission fluid for power steering fluid in my Nissan or a Lexus LX470?”. I was told that both the Lexus LX 470 and the Nissan will be fine if I used automatic transmission fluid instead of power steering fluid.

They told me that as part of my vehicles’ preventative maintenance service, I should periodically flush the fluid using a turkey baster or similar. Do this drain/fill procedure each day after driving the car until the fluid looks fresh and clean.

Using ATF In A Hyundai As Power Steering Fluid

Hyundai is very particular about the fluids used in the power steering system of their cars. While Hyundai does allow owners of the vehicles they manufacture to use generic power steering fluid, unlike Ford, Chrysler and GM vehicles in which using an automatic transmission is fine, ATF can cause an abrupt power steering system failure when used in a Hyundai.

Plus, using automatic transmission fluid as power steering fluid can also
void the vehicle’s warranty. The Hyundai power steering system is designed to use only mineral based power steering fluid. Using automatic transmission fluid would damage it.

An Acceptable Substitute

Many automobile service technicians say that in most vehicles manufactured between 1980 and 2000, it’s acceptable to make the substitution. They point out that if the vehicle comes with power steering fluid that’s a reddish or purplish color, then more than likely it’s really just ATF.

They say that the manufacturers use automatic transmission fluid instead of power steering fluid. For example Dexron III and other types of automatic transmission fluid consists about 85% base oil and 15% additives. This enables it to be used as a relatively safe substitute.

Select The Right Automatic Transmission Fluid

Even experienced auto repair specialists acknowledge that selecting a type of automatic transmission fluid that is compatible with the power steering system of many cars can be a tricky process. They are quick to point out that the specific viscosity, additives and friction coefficient of different types and brands of transmission fluid can vary widely.

Many car care technicians in favor of using automatic transmission fluid to replace power steering fluid agree some types of transmission fluids are safer to use than others. They say the best one to use is Dexron III.

Mixing Transmission Fluid With Power Steering Fluid

Another common question car owners ask is if it is safe to mix transmission fluid with power steering fluid. Some old school car care experts say as both are hydraulic fluids mixing them should not cause any problems.

Many modern automobile technician say if you plan on using automatic transmission fluid to replace your car’s power steering fluid, mixing them may not be a good idea. Although it may happen accidentally with minimal problems, ideally it would be best to flush the power steering fluid out of the car’s power steering system and replace it with transmission fluid. That is the safer option if you want to be sure to avoid unwanted problems.

Beware Of Multi-Vehicle ATF

Many companies claim their automatic transmission fluid can be used as power steering fluid in multiple vehicles. Be very careful which one you use in your automobile. This is particularly important if you have an Audi, BMW, Mercedes Benz or a Hyundai. These vehicles require a very specific type of power steering fluid or their power steering system will be damaged and no longer function properly.

While automatic transmission fluid may be able to be used in a pinch in Ford, Chrysler and General Motors cars, if it is used in most German cars and some Japanese cars it can lead to expensive repairs.

Check The Manufacturer’s Recommendations

If you want to be sure can you use transmission fluid for power steering fluid in your car, check the manufacturer’s recommendations in your car’s owners manual. Mixing the two can create corrosive, destructive, acidic substances. The manufacturer will tell you if transmission fluid can be used as power steering fluid in your car.