I picked up some Lucus heavy duty high performance SAE 80W-90 gear oil the other day.. can I use this to change my lower unit oil , Mercury Optimax, 225 ,, dealer has always done this, but I’m wanting to myself, any information would be appreciated..

I don't believe so. I don't recall the proper weight, but it's not as thick as the 80/90 wt. differential oil. Also the plug seals are like $2 a piece but I would replace them. Lower units are not cheap. You know what they say "water and oil doesn't mix".

Why would u replace the seal plugs?? They just screw in and out?

The seals on the plug (o-ring).

🤔 ok I gotcha ...

Been running 80 90 on my 225 all along and it’s a 1994 and still running. I have resealed the lower unit 3 are 4 times over the years. I’m not talking about the little plug o-rings. You need to teach yourself and your kids how to replace the water pump. I’m old now and the kids do all of that now. I check for water often and am always shocked when I find water in the lower unit ( but dam glad I checked to see) water is a killer. The first you find water you will check more often after that. Seals are cheap.

I guess you know to pull the bottom plug real quick and then replace it to check for water in the grease. If you don’t that is how it’s done. That water is the death of your lower unit. If you pull it enough times you will find water. That fishing line behind your prop will get under the seal lip and allow water to enter. Everyone may already know this but if it saves one lower unit so be it.

Mercury and Quicksilver are the same thing. You don't want to use a regular oil in a lower unit. This stuff and any good marine lower unit gear lube will protect your lower unit if there is any water intrusion. Not perfect if you leave water in there for a long time but without this special protection your lower unit innards will start corroding as soon as water gets inside.

Yes use the above, I think 80W-90 is more preferred for smaller outboards under 100 HP

lucas makes great products,but they have a full synthetic lower unit oil for marine lower units,it has a additive package more suited for outboards,the oil you have is a great one but it is not for marine use,

I use Lucas full synthetic M80 Marine Lower Unit oil & have for years. Yes, you DO need to get the M80 Marine Oil for lower unots, not the automotive/truck 80-90 weight.

Lucas M80 marine oil has additives to prevent foaming & regular Lucas 80-90 gear lube doesnt. Air bubbles in lower unit gear oil allow wear/heat build because gears arent 100%fully covered in oil.