Whats the best lower unit gear oil?

[hydro13]

Want to change the lower unit gear lube on my 2.5 260 HP with sports master lower unit....
What is the best lube to put in it? How much goes in it?


Thanks for the input

[D.B.S]

Merc Hi performance

[Ted Stryker]

Merc Hi performance

Yep, and fill it from the carrier until it start to flow from the top hole then some will flow back out from the fill hole as You try to get the plug back in and that's about enough... I can't remember the ounces, but I'm thinking it will actually hold about 28 oz. but is designed to operate with about 24(ish) oz... I may be wrong, but that's what is coming to mind...

[mcyama]

Tried and True 85-140 petro base when it comes to durability. Thanks Martin

[flabum1017]

Tried and True 85-140 petro base when it comes to durability. Thanks Martin

get a little water in it and the bearings are done, with the merc stuff, there is a good chance nothing will be damaged.......

[Ted Stryker]

The 85-140 won't hurt anything, I've used it to top of in a pinch but the Merc 90 weight is more suited for this application, so sayeth the engineers and chemist that are smarter than most... Oil viscosity is a function of operating temperature, and in this case You will almost certainly be better served with 90 weight...

[h2oskiier30]

22.5 oz for a sportmaster...according to the Merc manual.

[Markus]

I would use a full synthetic marine gear lube such as the Pennzoil product. It will not be quite as good at dispersing water as the Merc stuff is, but it will provide much better lubrication.

[sho305]

I've experimented a little with lube in far less powerful motors. In my old I/O that takes a gallon I ran 140 and then went to 90, gained some speed for sure. In my little 85hp I ran normal 90 marine lube then synthetic lube, gained 1-2mph. Then I got some straight 40 motor oil and put about 20% in with the synthetic and gained another half mph or so hard to tell. Since that was an 85 and they use the same LU for the 140hp I figured it was low stress and I could get away with it, didn't put many hours on it either. Of course with a more expensive and high performance outboard than a force I would only use highly recommended lube or synthetic. The same rated synthetic is typically not quite as thick, I am pretty sure that is one reason it makes more power and why I tried mixing even lighter oil in just to see. Of course LU gears are very high stress so not a good idea with big HP. Back when we ran Bravo outdrives we ran only Merc lube, and we changed it very often like a month of weekends often. We had no problems with 500hp built 454s we ran for years on them.

[Euro Muscle]

I always run (100% Synthetic) KLOTS SAE 90 gear lube in all my boats its good stuff. my 2 cents

[Scott in MN]

I always run (100% Synthetic) KLOTS SAE 90 gear lube in all my boats its good stuff. my 2 cents

I ran the Klotz stuff for one month with a leaking CLE. Everytime out I would change lube and drain a pink milkshake out of the lower unit but it held together so I would say the Klotz is good. Now I run the Merc high perf. but would use the Klotz no problem.

[Cp]

Merc Hi-Perf is the ONLY way to go. With it, a little water intrusion does NOT toast the gears. I don't think even Klotz will perform like that. It's always less painful (wallet) to replace a busted seal than all the hard parts too. I've been there and experienced it, both ways.

Oh, and with the Sporty, you need to let a bunch of it drain out before putting in the carrier seal. Other wise it will either push through the shift shaft seal, or blow the prop shaft seal.

[Jay Smith]

Merc High Performance in a recreational L.U. is hard to beat.

If I were drag racing trying to extract every ounce from a combo I'd run the Alyson 0 weight.. I have even used ATF at a race but changed to Merc oil while testing...


My .02
Jay

[sho305]

Merc High Performance in a recreational L.U. is hard to beat.

If I were drag racing trying to extract every ounce from a combo I'd run the Alyson 0 weight.. I have even used ATF at a race but changed to Merc oil while testing...


My .02
Jay

While racing sure lol. I bought a little turbo car once and after a couple months got tired of the notchy shifting, bought some synthetic lube. I went to drain it and I thought it was full of water at first, must have been pure clear mineral oil. Shifted much better after that. Likely some stupid kid saw that trick on the internet or something, it was not a race car and he could have bumped up the boost for way more improvement like I did.

[Ron V]

Bel Ray #413 is comparable to Merc Hi Perf and I've been running it for several years. Smells the same, looks the same, seems to protect the same.

Something that is being forgotten is that while lower unit gears are relatively small for the amount of power being run through them, the lower unit is also cooled by water constantly, unlike an automotive differential. The lake is also a huge shock absorber. I know guys who run the same oil (automotive hypoid, no less) for multiple seasons and it looks fine, never give it a second thought. But in something like a 2.5 it is very, very cheap insurance to change often and run the good stuff.