How to Change the Oil in a 2003 Harley Davidson

by Chris GillilandUpdated November 07, 2017
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Items you will need

  • Oil catch pan

  • Torx socket set

  • Socket wrench

  • Oil filter wrench

  • Engine oil, 20W50 (3 Quarts)

  • Drain plug O-rings (3 total)

  • Primary fluid (1 Quart)

  • Transmission fluid (1 Quart)

  • Shop towels

Regular oil and fluid changes are a key ingredient to maintaining your Harley-Davidson motorcycle. If left unchanged, the oil will break down over time, losing the lubricating properties that protect the motor and transmission form damage. Unlike other manufacturers, Harley-Davidson's V-twin motors use three separate oils: engine oil, primary fluid, and transmission fluid. All three must be changed regularly to extend the life of your ride, a process that can be done fairly easily with the right tools.

Engine Oil

Locate the engine oil drain plug and place your oil catch pan directly below it. On most models, the drain plug is located under the right side of the motor, next to the frame rail. Sportster models are equipped with a drain hose that is connected to the oil tank instead of the motor. Remove the drain plug and allow the oil to drain completely. Clean the drain plug and replace the O-ring before reinstalling the plug onto the motor or drain hose.

Remove the oil filter with a filter wrench and discard it. Prime your new oil filter by filling it with oil and install it by hand onto the motor. Add up to 3 quarts of engine oil into the motor or oil tank.

Start the motor and slowly loosen the oil filter until oil begins to seep out from between the filter and motor--this will bleed out any air that may have been trapped in the oil system. Tighten the filter immediately and stop the motor. Wipe away any spilled oil with a shop towel.

Primary Fluid

Locate the primary drain plug on the motor's left primary housing. The drain plug is located under the round derby cover on the primary. Place your oil catch pan below the plug and drain the primary fluid completely. Clean the drain plug replace the O-ring before reinstalling the plug onto the primary housing.

Remove the derby cover and gasket from the primary housing. Pour fresh primary fluid into the primary housing through the derby hole. Fill the primary until the fluid is touching the base of the clutch diaphragm spring.

Reinstall the derby cover and gasket. Wipe away any spilled primary fluid with a shop towel.

Transmission Fluid

Loosen the transmission fluid filler cap on the motor to quicken the draining process.

Locate the transmission drain plug. The drain plug is normally centered on the back of the motor. Softail models place the drain plug between the rear shock absorbers. Place your oil catch pan beneath the drain plug and drain the transmission fluid completely. Clean off the drain plug and replace the O-ring before reinstalling the plug.

Remove the transmission fluid filler cap and slowly add up to a quart of transmission fluid through the filler neck. Replace the filler cap and wipe away any transmission fluid that may have spilled with shop towel.


Warm up the motor before beginning the task to speed up the fluid draining process. Warm oil will flow faster and easier than cold oil. If you lack the tools to complete this task, have the work completed by a qualified Harley-Davidson technician.

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