How Often to Change Subaru Differential Fluid

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How Often to Change Subaru Differential Fluid -

Most car owners take great care of their cars. However, many experts argue that differential fluid is the last maintenance item owners trouble themselves with. However, neglecting differential oil cannot only lead to numerous car problems, leading to a complete breakdown, but the repairs are also expensive. Keep reading to find out what differential fluid is, why it is essential, and how often to change Subaru differential fluid.

What is a vehicle differential?

A differential is a device composed of gears, and it is used on all vehicles. The differential transmits power from the driveshaft to the wheel axle. The main objective of the differential is to allow your wheels to turn at different rates when you go around corners.

The most common type is the open differential. It is basically formed of two halves of an axle that have gears attached on each end, connected altogether through a third gear. Sometimes, a fourth gear is added to make it stronger and last for longer, and it ends up looking like a square. A ring gear is then added to this unit, holding the basic core gears. The ring gear transmits power to the wheels by being connected to the driveshaft through a pinion. The open differential is basic, cheap to produce, and it fulfills the main objective of allowing the wheels turning to move faster than the other wheels.

vehicle rear differential
Differential cap closeup – Img creds: SLworking on Flickr

An improved version of the open differential is the locked differential. This is most common with off-road cars; this locked differential can be locked to have a fixed axle (not independent as in the open differential). The differential mechanism of locking can be either electronic or manual, according to the type of technology used on your vehicle. The main advantage of the locked differential is that it has much more traction than the previous type, making it suitable for uneven ground and off-road driving.

A less common type of differential is the spool differential; it is often used in special circumstances, such as vehicles used for drifting. The spool differential operates similarly as the locked differential; however, it is welded into a fixed axle. This allows both wheels to spin at the same time. This is not often used because it incurs relatively high risks – for instance, the welding generates heat, compromising the strength and possibly leading to part failure. In the worst-case scenario, this can lead to the differential gears exploring through the differential casing.

What is differential fluid? 

Differential fluid is the oil found in the axle housing. It has a relatively thicker consistency compared to motor oil, and its purpose is to perform under very high pressure, unlike motor oil which performs well under high temperature. The differential fluid works under high pressures, such as gears grinding together and the hydraulic nature of a clutch pack.

Differential fluid, in the first place, helps your car to equally distribute the power to all the wheels, while accommodating for such differences when needed, for instance, when wheels are turning, so this is why it is called differential. More simply, differential oil allows your car to balance the power as when you turn, the turning wheels have more distance to travel than the others – thus, the fluid helps you to turn without losing control or skipping.

Differential fluids are used by all vehicles – whether you have an SUV, a large truck, or a two-wheel drive coupe. Four-wheel vehicles have three differentials: in the front, back and one which is centered. All of the three differentials help you with the differences between the speeds of the two sets of wheels: front and rear.

When your differential comes in to even the distribution of power from the engine to the wheels, the differential turns approximately 5,000 times in a minute. The differential is made up of metal gears; therefore, without proper lubrication, the differential wears down quickly, putting you in danger. This is why we need differential fluid. It’s equally important when you have a high performance vehicle like a Subaru race car.

Differential oil versus motor oil

We all know how important motor oil is. However, the differential fluid does not have an oil filter, like motor oil does. What does this mean? Well, if your differential fluid is bad quality, the differential might start having unwanted friction, which can lead to significant damages to the differential.

Differential oil is a sub-type of motor oil; however, it is slightly thicker, and it purports to allow your wheels to turn at different rates. The thicker consistency, or the higher viscosity, means that the differential fluid will not infiltrate the gears of the differential, but rather the differential oil will coat the gears.

So, in the end, differential oil and motor oil are not the same. Differential oil lubricates the gears of the differential without penetrating the inner workings, and it is not appropriate to be used as motor oil. On a similar note, engine oil is not suitable to be used for lubricating differentials.

How does it work?

Differential fluids come with ratings: for instance, GL-1 is the lightest rating, for easy operating conditions and specific types of differential gears. On the opposite side, there is GL-6, which is used in harsh conditions, such as shocks.

When you drive your car, the differential fluid sticks to and coats your differential gears. More specifically, it is continually lubricating the ring and pinion gears which transfer power from the driveshaft to the wheels. So, the primary purpose is to lubricate your differential. If you do not have any differential fluid, the differential will have metal to metal contact, which will overheat the gears and make your vehicle inoperable.

How often to change Subaru differential fluid?

Subaru cars are well known for their excellent reputation, especially in terms of being a low-cost car from a maintenance perspective. These vehicles retain their capacities over the long term. However, it is essential to ensure proper maintenance to make the best out of your Subaru experience.

The main advantage here is that differential fluids do not need to be changed as often as motor oil.

It is highly recommended that you get your Subaru differential fluid changed every 15,000 to 30,000 miles.

This also depends on your driving habits. Are you driving in rough conditions for long periods of time? Do you take advantage of the extra horsepower from your WRX performance parts? Or are you just driving to the local supermarket? It is vital to keep track of this and ensure that the manufacturer approves the differential fluid used.

A short guide to changing your differential fluid

One of the easiest methods to change your differential fluid is, of course, going to an ASE certified mechanic and letting the experts do their jobs. If, however, you are an ambitious car-lover, here are the steps on how to change your differential fluid on your own.

First, watch this vid!

MrSubaru1387 did a great job showing how to do a diff fluid change on a 2002 Subaru Outback. Check it out if you wanna try this yourself!

As we have discussed, differentials can differ slightly from car to car. Some make it an easy job; some make it more complicated (and messy!). So make sure you have lots of patience and a few supplies.


  • Firstly, drive your car for 5-10 minutes to get the oil warm. Then, put on mess-friendly clothes, grab a wide catch pan and a plastic drop cloth beneath.
  • The second step is to become mentally prepared – yes, that is right. This is because old differential fluid is the worst smell in the whole automotive universe. Keeping this in mind, proceed to remove the fill-hole plug from the top of the differential casing and unscrew the drain plug. If there is no drain plug, unscrew the housing bolts, leaving a couple of them loosely in place to keep the cover in place.
  • Get a standard screwdriver and pry open – very gently – the cover. If you do not act gently, you have a high chance of spilling the oil on yourself. Also, pay attention not to damage the surface of the differential housing. Drain the oil completely and remove the cover.
  • The next step is to wipe the remaining oil from the housing and the housing cover, from the gears. Clean with extra patience all the crannies and nooks to the tip of the fill-hole plug.
  • If your vehicle does not have a premade gasket, you can use a liquid gasket product especially made for oil exposure and harsh conditions. Put one bead on the mating face of the cover and circle around every mounting hole. Bolt the cover in place, just tightly enough to flatten the drop. Let it dry (harden), then use a torque wrench to tighten the bolts.
  • Now the last part – make sure you use the oil recommended by your manufacturer – that is, the highest quality possible. You can have a thorough look into the owner’s manual for more details – some cars might need an additional friction-modifying additive, such as those using limited-slip differentials. You will find all this information in the owner’s manual.
  • If you have enough space, fill up the differential from the bottle. However, you can use a hose or a pump if space is too tight or uncomfortable. When the oil starts to drip, you are done. Put in the plug, torque it (hand tight and then a quarter-turn with a wrench), and you’re good to go!

Wrapping up

Front Differential repairs are not cheap!

Taking care of your car is an important job – especially because it makes the difference between a safe or an unsafe journey. Most car owners do not pay attention to their differential fluid. But if you have reached this far, you will have gained some insights into differentials, what they are, and what they do. Lastly, you can either go for a specialized service to change your differential fluid or simply do it by yourself.

Pro Tip
Got a Subaru? Check out more of our Subi guides including, The Truth about Subaru’s Head Gasket Problems and the Best Battery For Subaru Outback.

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