Changing your 1999 Subaru Legacy Outback’s rear differential fluid can be a time-consuming process, but it isn’t very difficult. Be sure to purchase a 75W-90 GL-5 rear differential fluid—preferably the one produced by Subaru—and take care to loosen and remove the differential fill hole bolt before draining the old fluid.
Though you may have never heard of it before, your Subaru’s rear differential fluid plays an integral role in keeping your rear wheels running smoothly, helping to keep the axle properly lubricated. This gives you a greater ability to navigate slippery road conditions and off-road terrain.
But if you’ve never changed your vehicle’s rear differential fluid before, you’ve come to the right place—licensed car insurance
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has put together the following guide detailing everything you need to know about buying, making use of, and replacing your 1999 Subaru’s rear differential fluid. Stick around till the end to find out how you could reduce your Subaru Legacy Outback insurance costs,
too! What is rear differential fluid–and why does your Subaru need it?
So what exactly is rear differential fluid anyway? What purpose does it serve, and why does your Subaru need to have it replaced?
At a base level, rear differential fluid can be described as a type of motor oil, one that lubricates your vehicle’s rear axle, helping your Subaru drive smoothly. More importantly, however—and this is how it diverges from conventional motor oil—rear differential fluid allows your wheels to spin at different speeds by delivering variable levels of torque to the rear wheels.
Now, that may not sound all that important if all you ever do is drive on city streets or the highway, but rear differential fluid makes all the difference when navigating slippery conditions, driving over uneven terrain, and going off-roading.
The best 1999 Subaru Legacy Outback rear differential fluid
If you’re looking for the absolute best differential fluid for a 1999 Subaru Legacy Outback, you’re in luck because Subaru sells their own rear differential fluid! You can find it online labeled as “Subaru 75W-90 High Performance Gear/Transmission Fluid
.” If this isn’t available, however, you can’t go wrong with any brand—save for Mobil 1—as long as it has a weight rating of 75W-90 and is labeled GL-5. When it comes to utilizing the right rear differential fluid, the “75W-90” rating means it’ll have the correct viscosity while “GL-5” simply indicates the amount of sulfur-based additives present in the oil, which help the lubricant operate as efficiently as possible.
Some alternative brands we recommend are:
Valvoline’s 75W-90 Synthetic
Castrol 75W-90 Synthetic Gear Oil
How often to change the 1999 Subaru Legacy Outback rear differential fluid
Generally speaking, rear differential fluid isn’t subject to the intense conditions of something like your vehicle’s motor oil, making it easy to forget about—in fact, your 1999 Subaru Legacy Outback owner’s manual may not even include exact intervals at which it should be changed. There are, however, a few telltale symptoms that may point to it being time to replace the rear differential fluid, including:
A burning smell coming from the rear gearbox
Unusual or abnormal vibrations while driving
Straining, howling, or whirring noises from the engine
But if you don’t want to put your vehicle through any undue strain or run the risk of damaging something, simply change your 1999 Subaru Legacy Outback’s rear differential oil every 30,000 to 50,000 miles—the closer to 30,000 the better.
How to change your Subaru’s rear differential fluid
Before you start the process of a differential fluid service
, consult your Subaru owner’s manual to confirm the exact specifications for your vehicle and gather the following tools: Fluid transfer pump or turkey baster
Step 1: Elevate your vehicle with the carjack and make sure it is sitting stable on the jack stands. Loosen the bolt on the rear differential’s fill hole with a 17 mm socket wrench and the breaker bar.
Step 2: Place your oil catch pan underneath the differential between the exhaust and the sub-rame
Step 3: Use a 19 mm socket wrench to remove the drain plug from the differential, making sure the oil catch pan is positioned correctly—the rear differential fluid will come out faster than you expect.
Step 4: Allow the fluid to drain thoroughly. While you’re waiting, clean the drain plug with a rag. Once it is clean—and the fluid has finished draining—put the plug and a new washer back in the differential and tighten it with a torque wrench.
Step 5: Remove the fill hole bolt you loosened earlier. Use a turkey baster—or, if you have one, a pump made specifically for refilling differential oil—to add the rear differential fluid to the differential until it starts pouring out of the fill hole.
Step 6: Replace the fill hole bolt and use a torque wrench to tighten it.
Congratulations! You’ve successfully changed your 1999 Subaru Legacy Outback’s rear differential fluid.
How to find affordable Subaru insurance
Keeping up with your Subaru’s maintenance schedule
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