Gearbox Oil Change on C34 Universal M25XP

Easy Gearbox Oil Change

Changing the gearbox oil is not something we do very often but it is a pain in the neck trying to refill the gearbox after removing the old oil.

Equipment required ( to do it my way )

• Socket & Wrench to fit the Dipstick ( I think ours is a 9/16" socket )
• Oil Extraction pump - I use the same pump to do an Oil Change on the Engine
• 3/8" plastic hose - OD diameter to fit the Dipstick hole, ID to fit the Oil Change hose.
• Clean up towels
• Fresh Gearbox Oil - there is a label on our gearbox 'Use Auto Gearbox Oil'

Here's how I change the Gearbox Oil on Eximius.

Prep the Oil Change Pump ( OCP ) and completely empty it of any previously extracted oil.

Remove the cabin steps to gain access to the top of the engine and use a socket and wrench to remove the Dipstick which is located on the Port Side forward edge of the top of the gear box. It's a challenge but once removed, wipe it down with a clean cloth and put it back in place but do not screw it down, instead just put it into the gear box and withdraw it then note the Oil level on the dipstick. Ours is normally at the groove in the dipstick. Now remove the dip stick again.

Ok, now we know what level the oil should be.

Again, leaning over the top of the engine, insert the 3/8" hose down between the heat exchanger and the back of the engine and insert the hose into the gearbox Dipstick hole.

Using that hose as a sheath, insert the Oil Change Pump hose down into the dipstick hole as far as you can, down into the gearbox dipstick hole.

Next, use the Oil Change Pump to suck out the Gearbox oil. Only takes a few pumps of the OCP handle.

Withdraw the OCP hose from the 3/8" sheath but leave the sheath hose in place.

Insert a suitable funnel into the top end of the sheath hose.

Now that the oil removed from the gearbox is in the OCP container, pour the old oil into a measuring cup in order to measure the replacement, new, oil.

With the correct amount of replacement oil in a measuring cup, pour it into the funnel that is in the end of the sheath hose.  Now the gearbox should have enough fresh oil that replaced the old oil.

Now remove the sheath hose and check the gearbox oil level with the dipstick, it should be the same as the original dip. If need be, add more oil by removing the dipstick, reinserting the sheath hose and funnel then add small amounts of oil checking between with the dipstick until the correct level is attained. Don't forget to reinsert the Gearbox Dipstick bolt!

Using the concept of the sheath hose makes it a whole lot easier removing and replacing the gear box oil when the fill point is really awkward to reach.  

It is possible, with a good bit of boat Yoga, to reach the Dipstick bolt from the top of the engine, but if that doesn't work for you then empty the aft berth, remove the sub floor and crawl down to reach the dipstick bolt just forward of the port top edge of the gearbox.

Note. I have read stories of owners that removed the gearbox oil drain plug and then had a hard time of getting a replacement sealing washer for the plug. However, draining the oil from the drain plug is the way to go if you want a 100% change.  Your boat. 

See you on the water.