What is differential fluid?

What is differential fluid? Going around corners without clattering, jumping, or jumping is something that’s easy to take for granted. That’s all thanks to the differential (sometimes called a transaxle), which is a component that compensates for the difference in distance the inner and outer wheels travel when the car turns corners.

The differential, which is part of the powertrain, helps evenly distribute the vehicle’s power to each wheel. The differential is what keeps you in control while turning.

The differential depends on the differential fluid to continue to operate in optimum condition. What is differential fluid? It is the oil that lubricates the internal components of the differential, such as the ring gear and pinion gear, so that the differential does not start to wear and cause major problems.

Brian Murphy, Universal Technical Institute (UTI) Education and Development Program Manager, Curriculum, shares more about why differential fluid is important and why it’s important to maintain it.

What does differential fluid do?

The differential fluid ensures that the differential remains in top working condition for a long time. Differential oil is sometimes called gear oil and is found in the axle housing. It is designed to work in high pressure situations, rather than high temperatures like motor oil.

Differential fluid:

  • Lubricates clutch packs, gears and bearings.
  • Lubricates the ring and pinion gears that move power to the wheel axles from the driveshaft.
  • Cools and lubricates the differential.

Without differential fluid, the differential would overheat due to metal-to-metal contact. That means it would burn out and possibly cause safety issues and require expensive repairs.

What does the differential fluid look like?

Differential fluid looks similar to motor oil but is thicker.

There are two types of differential fluid. One is mineral oil, which is a natural fluid based on crude oil.

The other is a synthetic differential fluid, which is created in a laboratory. As with all synthetic oils, synthetic differential fluid oils can be tuned for optimum performance.

What is rear differential fluid?

Rear wheel drive vehicles use a rear differential but not a front differential. A front wheel drive vehicle will use a transaxle, which is part of the transmission. Rear differential fluid is used for rear wheel drive cars.

The trucks use the same fluid in both the inter-axle differential and the rear differential.

How often should the differential fluid be changed?

The answer depends on the manufacturer. It is always best to check your owner’s manual for the proper service interval. In most cases, you will need to change your differential fluid every 30,000 to 50,000 miles.

It is important to keep track of the differential fluid change because metal-to-metal contact creates heat from friction. It also weakens gears and wears down surfaces. That can lead to differential failure, which is a costly problem.

What happens when differential fluid levels are low?

When differential fluid levels are low, the gears will begin to grind, which can cause differential failure.

Unlike motor oil, which works with an oil filter, differentials don’t have a filter. When a differential experiences unwanted friction, small chips or pieces of metal can appear and cause significant damage to the differential.

What is differential oil?

Where there are gears there is friction. Enter differential oil to help prevent that friction. Gears work together, and the harder they work, the hotter they get. As with the motor oil in your vehicle, differential oil lubricates the differential gears to reduce the friction they generate and therefore heat. In fact, differential oil is very similar to motor oil with a few differences. Differential oil is thicker than motor oil and is also more viscous. It sticks to gears to coat them and penetrates the inner workings of the gear. However, don’t think of differential oil as motor oil. They are classified separately and have different roles.

What does differential oil do?

As we mentioned in the previous paragraph, the differential oil lubricates the differential gears. As the oil ages, it can break down and become less effective. Old, damaged, or even leaking differential oil can damage gears. Common problems associated with differential oil failure include gears that overheat and seize or break. That’s why it’s important to check your owner’s manual to see if you have a gearbox, and if so, when you need to change the differential oil. This prevents costly car repairs, although we can repair and even replace your gearbox if it has been damaged.

How to take care of the differential of your car

Changing the automotive differential oil is one of the most overlooked maintenance tasks on light trucks, SUVs, and passenger cars without front-wheel drive. Because the diff is at the rear and under the car, it doesn’t get the star treatment that the engine gets in the front.


But if the car’s differential lubrication fails, you won’t get far for long. Fortunately, you only need to change this oil every 30,000 to 50,000 miles.

The differential is a component in every car and is designed to make up for the difference in the distance the inner and outer wheels travel when the car turns a corner. In a rear-wheel drive car, the differential has its own housing and lubrication, a thick, dark oil that typically weighs over 80 pounds.


Front drivers typically integrate the differential into the transmission case and share the same fluid. Differential oil lubricates the crown and pinion gears that transfer power from the drive shaft to the wheel axles. If your car is equipped with a limited slip differential, it also keeps all the moving parts in that assembly healthy.

A differential allows your car to take corners without drama. If both drive wheels rotated together, they would jump because the outside tire travels further than the inside. There are many variations on the design, but they fall into three categories: open, limited slip, and torque vectoring.


Changing this oil is just as important as changing your engine oil and for the same reason. Metal-to-metal contact wears down surfaces and creates frictional heat, which inevitably weakens gears and leads to failure. Checking and changing the differential oil on a light truck is fairly easy, and it’s only slightly more difficult on a car.

prepare the area

Depending on the design of your differential, this can be a very messy job or a very neat job. Some differentials have a drain plug; others require you to remove the case cover. In either case, you’ll need a wide catch tray; a plastic sheet underneath would be good insurance. Drive your vehicle for a few minutes to warm up the oil, then change into your dirty clothes, you’ll probably get dirty.


It’s just an oil change, right? Nothing too complicated, but be prepared, because old car differential oil has the worst odor in the automotive world. With that warning, remove the fill hole plug at the top of the differential case, then unscrew the drain plug. If you don’t have a drain plug, unscrew the casing bolts, leaving a couple of bolts at the top loosely attached to hold the casing in place.

Using a standard screwdriver, carefully pry the lid open or the oil will gush out and cover you in that unholy stench. Be careful not to mar the surface of the differential case. Let the oil drain completely, then remove the cap.

Clean everything up and seal it

Assume that all the excess oil in the shaft is loaded with metal shavings. If you’re a Boy Scout changing your oil, you don’t have to worry about this, but the rest of us should take the time to clean any remaining oil from the housing, gears, and the wet side of the housing. cover. Make sure you get it all, because there might be a few chips hiding in the nooks and crannies.


Also clean the tip of the filler plug; most are equipped with a magnet to grab fine metal particles. Don’t go crazy with harsh cleaners, you don’t want the residue to affect your new oil. Take a knife scraper or light abrasive pad and clean the mating surface of the housing and cover. Clean both sides with a lint-free shop towel and brake cleaner.

Some cars have pre-made joints. Otherwise, use a liquid gasket product designed for harsh conditions and oil exposure, such asPermatex ultra negro. Place a single bead on the mating face of the cover and draw a circle around each mounting hole, then screw the cover into place with just enough clamping force to flatten the bead. Allow to harden according to the instructions, then torque the bolts to your vehicle’s specifications with a torque wrench.

fill to the brim

Use the highest quality gear oil you can afford to fill the differential. Weight and capacity will appear in the owner’s manual; your differential will usually have up to 3 quarts. Be sure to read that manual though, because some limited slip differentials require a secondary friction modifier additive.

Fill the diff directly from the bottle if you have room to spare, but if space is tight you can get a pump or extension hose to make the job easier. The bottom of the plug hole is the max fill line, so when the oil starts to drip, you’re done.


Differential oil, which is also known as gear oil, is thicker compared to engine oil. As a lubricating oil, gear oil prevents damage to metal vehicle components and increases overall performance. The oil also makes it easier for cars to take turns smoothly.

Heavy-duty automotive fluid works at high pressure to ensure all gears, clutch packs, and bearings are continuously greased, keeping all differentials running smoothly and safely.

If gear oil runs out or becomes dirty or contaminated with water, metal components can be permanently damaged. To avoid damaging transmissions, clutch packs, and differentials, you need to be on the lookout for the symptoms of bad gear oil.

Burnt smell from differential

When you notice a bad smell coming from your gearbox, you should take it as a sign of bad differential oil which may be contaminated and therefore not working as it should. The bad smell is an indication that the gearbox is overheating because the lubricating oil has run out or is dirty and cannot properly grease the gears.

The oil may also be out of date or too old to lubricate vehicle parts, causing the same bad smell because metals will burn due to metal-on-metal friction. Once you realize that your differential oil is contaminated, the next step is to replace it immediately.

weird noises


Another symptom of bad differential oil is strange whining, whining, or whining, indicating that the metal parts, clutches, gears, and differentials have not been lubricated due to a lack of clean, dirty oil.



If you’re driving and feel unusual vibrations, this may be a sign of a bad differential or gear oil. However, it may be a sign of other automotive problems that need to be checked out by a professional mechanic.

Strange noises increase each time your vehicle turns and when speed increases. For that reason, you should take your vehicle to a reliable and professional mechanic to make the necessary checks and fix the problem.

To repair the gears and other metal parts, our professional and trained mechanics can perform the task. If you need differential repair, call our auto repair shop today!

What is differential fluid, gear oil or gear lube?


A differential is a set of gears that allows a vehicle’s drive wheels to spin at different speeds when turning corners or on uneven terrain. Those gears require lubrication, which is commonly called differential fluid, gear oil, or gear lube.

Modern vehicles produce substantially more horsepower, torque, and towing capacity than their predecessors, yet the design of the differential gears and bearings remains largely unchanged.

To reduce drag and increase fuel economy, many modern differentials also use less gear lube and lower viscosities. So less gear lube is responsible for providing more protection in a modern differential. Add trailer to the mix and you need heavy-duty lubrication.

fighting the routine

Differential designs have inherent weaknesses. In a traditional automotive differential, the pinion puts intense pressure on the crown. As the gear teeth mesh, they slide against each other, separated only by a thin layer of lubricant.

Repeated stress placed on the lubricating film can break down gear lubricants, causing permanent loss of viscosity. Once sheared, the fluid film weakens, ruptures, and allows metal-to-metal contact, eventually leading to gear and bearing failure. Severe-duty applications, like towing, amplify the situation.

Thermal escapes

The extreme pressures and temperatures applied to gear lubricants can also cause a serious problem called thermal runaway.

As temperatures in the differential increase, some gear lubricants lose viscosity and load capacity. When extreme loads break the lubricating film, metal-to-metal contact occurs, increasing friction and heat. This increased friction and heat, in turn, results in a greater loss of viscosity, which further increases friction and heat.

As the heat continues to spiral up, the viscosity continues to spiral down. Thermal runaway is a vicious cycle that leads to extreme wear and eventually catastrophic gear and bearing failure.


Severe service operation requires more frequent differential fluid changes. Most vehicle manufacturers recommend changing the differential fluid every 150,000 miles in normal service, but dramatically reduce the change interval to every 30,000 miles when towing frequently in temperatures above 70°F. That goes for anyone pulling an RV, boat, or trailer during the warmer months.

Take it easy

AMSOIL GEAR SEVERE is designed to resist breakdown from extreme heat, helping to prevent viscosity loss and acid, carbon and varnish formation. Its wax-free formula also improves cold flow properties for better cold weather performance.

SEVERE GEAR is also available in award winning AMSOILeasy pack. Its flexible design makes performing complicated and hard-to-reach gear lube changes easier, faster and cleaner. No more broken knuckles, annoying gear lube pump, and stiff bottles that waste half your fluid.

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