How to Check Your Car's Differential Gear Oil

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The gears inside your car's differential enable the drive wheels to spin at the right speed when you step on the gas pedal and at different rates when you turn a corner. The gears are coated with a film of oil that protects the hardened steel layer on their teeth from friction wear. Periodically, the differential gear oil must be checked to be sure there is enough to protect the differential; here's how to do it.

Steps

1. 1
   Park your car on a level surface. The car must be kept level to get a true reading of the differential gear oil level. If the car is not level, the oil may flow to one side of the reservoir.

   
   
2. 2
   Place the car on jack stands. Jack up the car with both the front and back on jack stands to keep it level.
3. 3
   Look for the differential. The differential is pumpkin-shaped and is located where the car's drive wheels are. If the car has front-wheel drive, the differential is in the front; if the car has rear-wheel drive, the differential is in the back.
4. 4
   Locate the differential drain bolt. The bolt is usually on the side of the differential, facing the rear of the car, although it can occasionally be located on top of the differential.
5. 5
   Remove the drain bolt with a wrench. Expect gear oil to seep out; if not, stick your finger in the drain hole to see how far the oil is from your finger. If you have to reach very far, you'll need to add oil.
6. 6
   Add differential gear oil if required. Differential gear oil is available from most auto-parts stores in bottles with attached pumps to add it to the crankcase. Be sure to use the weight and GL rating of differential gear oil called for by your car's manufacturer.
   • If your car has a limited-slip differential, which can detect whether a wheel is on a slippery surface, your differential gear oil must contain special lubricants to enable the differential to do its job properly. As different auto manufacturers use different mechanisms, each requiring its own lubricants, you must use the gear oil called for by your manufacturer if you have a limited-slip differential.
7. 7
   Replace and tighten the drain bolt. Wipe away any excess differential oil from the gear case, and check to be sure no fluid comes out after you've tightened the bolt.
8. 8
   Lower the vehicle carefully to the ground. Check again for gear oil leaks.

   
   

Tips

• Check your car's owner's manual for how often you should check and change the differential gear oil under normal driving conditions. If you do a lot of towing or submerge the differential under water, you'll have to check and change the gear oil more often. (If the differential has to be drained when the axle it's attached to needs to be serviced, it's common to change its gear oil then.)

Warnings

• Differential gear oil contains sulfur compounds that give the fluid a strong rotten egg smell that will impregnate whatever clothing it gets spilled on. When checking your differential gear oil level, it's a good idea to wear old clothing that you can discard if necessary.

Things You'll Need

• Jack
• Jack stands
• Wrench
• Differential gear oil and pump
• Rags or paper towels

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