Differential Gear Oil Fluid Check

Step by step instructions on how to check and add gear oil to an automotive differential. This article pertains to all rear wheel vehicles.

Difficulty Scale: 3 of 10

Tools and Supplies needed

  • Flashlight
  • Appropriate 3/8 ratchet, socket or wrench
  • Gear oil
  • Shop towels
  • Protective eyewear and gloves

Start with the vehicle on level ground, safely lifted to access the differential fill port, use jack stands to support the vehicle.

Step 1
- Locate the gear oil fill port on the differential housing or rear cover.

Gear Oil Fill Port

Step 2 - Once located use the appropriate tool to remove the fill port plug.

Remove Gear Oil Fill Plug

Step 3 - After the plug has been removed, insert a finger or wire into the fill port.

Insert Gear Oil Level Checker

Step 4 - While inserted the indicator will leave a gear oil trace when removed. (Note: do not turn drive shaft or rear wheels while checking the gear oil level.)

Level Indicator Inserted

Step 5 - When removed the indicator will show gear oil or not. If gear oil is not shown, the fluid is low and additional fluid is needed.

Gear Oil Indicator

Step 6 - Using the appropriate gear oil, add to the differential until gear oil seeps from the fill port.

Adding Gear Oil

Step 7 - Gear oil will seep from the oil fill port once the gear oil level is sufficient.

Gear Oil Full

Step 8 - After the differential has been filled, recheck the level with an indicator.

Full Gear Oil Indicator

Step 9 - Then, reinstall the oil fill plug and tighten.

Reinstall Oil Fill Plug

Step 10 - Once the oil fill plug is tight, clean excess gear oil from differential using a shop towel.

Clean Excess Gear Oil

Helpful Information

When after checking a differential fluid level, inspect the unit for leaks such as a rear axle seal. Always maintenance a differential and service the gear oil on a regular basis to ensure continuous operation. Knowing how a differential works also aids in troubleshooting noise related problems.

Best Practices

  • Use quality gear lubricants
  • Use manufacturer recommended fluid and additives
  • Inspect the differential for leaks shortly after adding gear oil


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published