Quicksilver synthetic in my Merc 30hp. It looks like new when I dump it in fall.
Marine Gear Oil for lower units
- Thread starter Snagglefoot
- Start date
No, they don't. Only marine drives that have leaky seals get water contamination.
I was told to my face by a Mercury factory rep its the same oil. That's good enough for me. I have been using Automotive gear oil for 40 years (as have local Marinas)
Well if that's true, then there is a pretty good reason to never buy Quicksilver's marine gear oil. Any formulator making a marine gear oil who isn't formulating for water emulsibility is either; negligent, ignorant, or just a plain ole' meanie......probably hates puppies too
- Joined
- Aug 2, 2020
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I have had a Volvo Stearn drive for 5 years. I have always run Mystic JT4. It states the it can be used in a Volvo Stearn drive.
I also run Mystic 10w40 in the engine.
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Im a fan of Mystik 15w50 JT8 for my Volvo engine. Also use it in my Harley.
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I have been using Mystic lower gear lube in my Volvo Penta Stearn drive for 7yrs. Not an issue.
At the end of the season, I remove the lower plug and let any accumulated water dribble out along with a bit of lube. I then quickly clean the magnetic plug, put it back in and leave it for the winter. In the spring I drain it completely and put in fresh lube. Here is the paper towel showing a bit of water, some lube and the reside from the magnet. It’s a 27 year old Yamaha two stoke. Maybe I’ll change the seals, maybe not. 
The black residue from the magnetic drain plug is mostly caused by towing a tube with my wife’s FA cousin on it. He weighs in at 220.
I have had Mercruiser for 10 or 15 years. New to me boat has a VP. Two things I like is the raw water pump is on the engine not stuck in the outdrive. And there is a bellows and a seal on the shaft to the outdrive. So a tear in the bellows will not sink the boat.
This VP engine has MPI and in order to warm up engine in 'N' at fast idle I need to go through some of the control options on the gauge vs just pull a knob to disengage the shift.
I would think its better for the water to sepatate, as water does not lubticate. Better have it at the bottom of the gear case, where it can be easly drained out. It the water stays in suspension you could have rusting on the bear metal surfaces. I have been using automotive gear oil since 1988 when I was told by a Mercury rep its all the same thing.
Rebuild of VP duoprop is $6000. Two year warranty. Given I only need a few QTs of VP gear oil and it's maybe $15 a QT, it seems a no brainer.
Thinking that water separation is a benefit because the free water can be easily drained off is not necessarily a benefit in a recreational marine drive. Separation is only a benefit if the water is drained before every use. This is okay for trailered boats but not for ones kept in the water.
A marine gear oil can be formulated to form a stable emulsion and maintain anti-wear, EP/AS and rust/corrosion protection in the emulsified condition. These are requirements of the Merc gear oil spec which is a difficult spec to meet. While this is true, as the level of water contamination increases so does the rate of failure.
I don’t really know but I would think an OEM that is oaky with automotive oils is also dependent on the owner performing maintenance and repairs as needed.
Even if the boat is left in the water, any water in automotive gear oil will (in theory) settle in the bottom of the lower unit, and not stay suspended in the gear oil. If it did stay suspended, where it is in constant contact with metal gears and bearings, it will cause rusting and pitting. It won't do any harm sitting in the bottom of the gear case. Local large marinas around me, all use automotive gear oil.
Also, I had an 18 Evinrude for many years, that had a bad prop shaft seal, I always used automotive gear oil. When drained in the fall, a milkshake always came out, and the water was always in suspension with the gear oil so maybe automotive gear oil does not separate as you claim? There is no difference, but you can all believe what you want. Some people think Snowmobile oil is made special for snowmobile engines
Also, I had an 18 Evinrude for many years, that had a bad prop shaft seal, I always used automotive gear oil. When drained in the fall, a milkshake always came out, and the water was always in suspension with the gear oil so maybe automotive gear oil does not separate as you claim? There is no difference, but you can all believe what you want. Some people think Snowmobile oil is made special for snowmobile engines
Do you really think automotive gear oil will trash your $6000 lower unit? As in, its Ok for a lamborgini rear end, but not my boat lower unit
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I do believe there are additives to deal with minor amount of water that might get in a lower unit gear housing And my $6000 rebuild has a 2 yr warranty. So it will get VP outdrive gear oil.
As far as price goes is Amsoil SVG gear oil any cheaper than VP gear oil?
