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OMC Cobra oil refill instructions

Instructions on how to fill your stern drive with oil, complete with photos and tech help

  • Lower gearcase photos
  • Links to technical drawings
  • Step by step oil filling instructions
  • Exploded view OMC Cobra drawing
  • GLM aftermarket replacement plugs and parts are available

By author Trish Dougherty

Cobra sterndrive has one cavity where the oil is stored, so all the oil in the upper and lower gearcase must be changed and filled at the same time.

Follow these easy steps to change the oil in your drive.

  • If you have not yet drained your oil, see our Draining your OMC Cobra's oil help page before filling your sterndrive with oil. To view technical drawings for upper and lower gearcases, see your I need help page.
For this job, you will need...
  1. Oil pump
  2. 2 or more quarts of oil
  3. Large flathead screwdriver
  4. Rags
  5. Replacement oil draining screw gaskets

OMC Cobra oil filling diagram

Oil filling diagram

Oil filling diagram

Start off by locating the lower drain screw/plug on the lower gearcase. (It is on the starboard side of the lower unit on the cone - shown in photo).

Remove this plug using the largest blade flathead screwdriver available. Insert your oil pump as snug as possible into the drain hole.

Cobra lower gearcase upper drain screw location
Lower gearcase upper drain screw location

Lower gearcase upper drain screw

Locate the upper drain screw/plug (shown in photo), and remove it using the same flathead screwdriver you used to remove the lower drain screw.

Begin pumping oil into the lower drain hole, and carefully watch the upper drain hole until you see the oil reach this level. When the oil just reaches the upper drain hole, close it up by inserting the upper drain screw.

(DO NOT STRIP the screw when making sure it is tight enough)

Lower unit oil pump
Lower unit oil pump

Lower unit oil pump

Remove the oil pump from the lower drain hole, and quickly insert the drain screw/plug.

Again, remove the drain screw from theupper portion of the lower gearcase, and quickly insert the oil pump into the upper drain hole.

Begin pumping oil to proper level on upper gearcase dip stick.

28404 cover o-ring
28404 cover o-ring

Dip stick location

On the top side of the upper gearcase, you will see a cover, with four large bolts attached to it. In the center of this cover or cap, you will see a 3/4" diameter flathead dipstick.

Remove it, and note where the oil level is. The oil level on an Cobra should be at the line on the dipstick. If it is not at this line, keep pumping in oil through the lower units upper drain hole.

When the oil reaches the line, put the dipstick back in. Remove the oil pump, and quickly insert the lower units upper drain plug. Make sure this screw/plug is tight, but be careful not to strip the screw.

Lower unit oil pump
Lower unit oil pump
Oil pump $12.29

21731 Draining screw washer
21731 Draining screw washer

Replacement oil draining screw/plug (includes 1 gasket) P/N 21731 Draining screw $9.99 OEM 318544

31171 Gasket
31171 Gasket

Replacement oil draining screw/plug gaskets (5 units) P/N 31171 Gaskets $4.89 OEM 311598

 28404 cobra cover o-ring 2
28404 cover o-ring 2
Replacement top cover assembly P/N 28404 Cover assembly $71.89 OEM 914489

21732 Dipstick
21732 Dipstick

Replacement dipstick for top cover P/N 21732 Dipstick $24.00 OEM 914488