Flushing the Lower Unit gear case

[Longrange1971]

Hello good people,
Well one of my worst fears has come to fruition. I have twin 2013 Suzuki DF 250's. while doing the yearly maintenance yesterday, i went to drain the lower unit gear case oil to replace. I always struggle to get the lower unit gear case plugs out and was not looking forward to the procedure. Much to my dismay, I found the starboard engine lower gear case plug was extremely loose. When i opened it a gray sludge dropped out. There was no oil left in the unit only grey sludge, and not much of it. Keep in mind, I do not know how long it has been this way as I change the lower unit oil last March and the boat was in the water all this past summer. The motors ran fine with no issues all the way up to include the trip to load it on the trailer for the winter. No gear case issues and the boat has been on the trailer since. I ran two quarts of gear oil through the unit, one from the top, one from the bottom to refill in an attempt to flush, then ran the motor with it in gear for approx. 5 minutes. Seems to be no ill effects, no noise in the unit etc.. I did notice that there is still some grey oil coming out mixed with the new stuff. My question is, is there a way to flush the lower unit without taking it apart and what are my chances everything will still be fine? Any advise would be greatly appreciated.

Thank you in advance.

[Harper]

You should just use the correct gear lube and continue to run it through till you're happy with the results. The use of anything other than a lube that is meant to lubricate helical gears risks damaging the unit. I don't think you have to get every single bit of the gray oil you're seeing out, but make sure that the last fill is of a quality marine gear oil. After a couple trips out on the water, you might drain and refill one more time and not worry about it any more.

[Longrange1971]

Sir that is great news. I hope that will be sufficient. When i flushed it I used 2 quarts of the Suzuki gear lube. That is all i have put in it. Your comments were exactly my plan. Run it a few times then drain and refill again. I will try to continue to do that until it comes mostly clean.

[Murray]

When you drain the oil let it drain overnight and tilt the engine slightly so your drain plug is pointing down. Remember to bring the engine back to vertical before refilling. If it’s not too late, buy a cheaper gear oil to flush (that meets Suzuki specs) then put the good stuff in.

[tsturm]

Use any 08-90 gear lube for your flush & trial runs. I quit buying the expensive "marine" gear oil 30 yrs ago. I use the cheapest automotive synthetic 80-90 I can find.
Zero issues in 25,000 hrs. of boating in that time. Hypoid Gear oil is gear oil!
Have a good one!!

[Longrange1971]

Thank you all for your responses. It is greatly appreciated

[Longrange1971]

Soooooo........ In your honest opinions, What are the chances this lower unit isn't already screwed up and that it will be fine. I'm just curious and was wondering if I should just take it somewhere to have it broken down and inspected. Like I said it ran fine the last time out before putting her on the trailer, but I just don't know how long it has been this way. I put 70 hours on the motors since the last gear oil change. Fingers crossed i guess. Is there any other way to check for damage other than breaking it down all the way.

[Harper]

If there's no unusual noises while running on the muffs, I'd say go with it. Go ahead and run it up in gear to 1000-2000RPM on muffs (or higher if you're brave ), and do that for half a minute or so. Also can see if you feel any unusual play in the prop with the engine stopped and the motor in gear. But if you don't hear any banging or howling while running you're probably okay. It won't be under load, but should be satisfactory as an indication, and you probably wouldn't be able to hear a problem with it in the water. Might be a good idea to run both in forward and reverse gears.

[Longrange1971]

Ran in forward and reverse with the muffs on. No noise at all goes into both gears smoothly. Checked the prop for any play and had none. Well very very little and was comparable to the Port engine so I'm hoping all is going to be ok. Also talked to my Suzuki mechanic. He said the Zuke lower units are tough as nails and if it ran fine on the last trip it should be no problem at all. Im starting to feel a lil better about this. Thanks for all the help.