How to Change Differential Fluid

What Is a Differential?

A differential is a device in a vehicle’s drivetrain that allows the wheels that are receiving power from the engine to move at different speeds.

Think about a car going around a corner. The wheels inside the corner have a shorter distance to travel than the outside wheels. The differential allows those wheels to get power from the engine while spinning at slightly different speeds. Without a differential, the inside wheel would skip, hop, and bind up as it tries to spin as fast as the outside wheel.

Almost every car on the road has a differential, with the exception of some electric cars that have individual electric motors at each wheel.

However, for this article, we are only looking at the differentials on rear-wheel-drive, four-wheel-drive, and the rear wheels of all-wheel-drive vehicles. The differentials on front-wheel-drive and the front of all-wheel-drive vehicles are contained within the transmission, so the procedures for changing the fluid are different.

How to Change Differential Fluid

Before you jack up your car, make sure you choose the proper differential oil. Differential fluids come in a number of different grades and viscosities. Each has unique properties based on the type of differential in which they’ll be used.

Some differentials require limited-slip additives that modify the amount of friction provided by the fluid. Always follow the manufacturer’s recommendations when choosing a differential fluid. Deviating from the standard can negatively affect how the differential performs.

Pro Tip

Put on clothes you don’t mind throwing away. Differential and gear oils often have a distinct smell of rotten eggs or decaying fish—scents you won’t want to wear to dinner after completing the job.

Next, you’ll want to gather your supplies near the car:

• Drain pan
• Correct new fluid
• Hand-operated fluid pump
• Wrenches
• Possibly a differential gasket or RTV silicone gasket maker

Now, you’re ready to begin changing the differential fluid.

Step by Step

1. Safely jack up the rear of the vehicle and support the rear with jack stands.
2. Locate the differential drain plug if equipped. Some vehicles don’t have a drain plug. In other cases, the drain plug might be damaged and cannot be removed.
3. Locate the differential fill plug and ensure that it can be removed to refill the differential with fresh fluid.
4. If the differential is equipped with a functioning drain plug, remove the plug and give the fluid time to drain into the pan. Most differential oils are more viscous than engine oil, so it might take longer to drain than a typical oil change.
5. If the differential does not have a drain plug or the plug is damaged, you will need to remove the differential cover. This typically requires removing several small bolts. Gradually loosen each of the bolts in a pattern: side to side, then top to bottom. This way, the differential cover won’t bend or warp out of shape. Then, remove the lowermost bolts altogether to allow the fluid to drain completely into the drain pan.
6. After the fluid drains, replace the drain plug or the differential cover. If you opened the differential cover, you will need to replace the differential cover gasket with either a new gasket or RTV silicone gasket maker. Then, replace the bolts and tighten them to factory specifications in a crisscross pattern, the same as you did when removing it.
7. Open the fill plug and stick a hose from the hand-operated pump inside. Pump fresh differential fluid into the fill plug until it starts to dribble out. After it’s filled to factory specifications, replace the fill plug.
8. Wipe up any spilled fluid, and lower the car to the ground safely.

Differential Fluid Replacement Cost

Differential fluid typically costs around $10 to $25 per quart, but most differentials need less than two quarts for a complete change. Replacement gaskets and silicone gasket materials typically run around $10 to $20 each, and a hand transfer pump for the fluid usually costs less than $20.

Replacing your differential fluid is neither difficult nor expensive, but it’s a critical preventative maintenance task to ensure long life for your drivetrain.