Lubing my unit....

[oldmako69]

2005 F225TURDs

Looks to me as though the manual calls for 80-90 weight gear oil. But, I have seen numerous references online to using 90 weight oil only. And that stuff is hard to find and pricey.

I am of the opinion that fresh cheap gear oil is far superior to old (dirty and possibly emulsified) high-end gear oil. Plus, it's really easy to drain and refill the LU's. When you consider what they cost to replace and how quickly the seals fail and allow seawater in, that's a great reason to change LU gear oil frequently. And when you consider how stupid an LU is, I can't fathom a reason to dump expensive lube in there. There's spending money and there's wasting money. For you, petroleum engineers out there, how much difference is there between 80-90 and straight 90?

Food for thought and comment.

[DennisG01]

The Merc Hi-Perf full synthetic stuff is nice - relatively inexpensive. Considering you only need a quart, or so, it's pretty cheap insurance to put good stuff in there. You're talking, literally, a couple bucks difference once a year. The Hi-Perf stuff can still protect your many-thousand-dollar lower unit if some water gets in. Normal gear oil will not.

[oldmako69]

"The Hi-Perf stuff can still protect your many-thousand-dollar lower unit if some water gets in. Normal gear oil will not."

I have never heard this. Will do some reading. MANY thanks. This is the type of info that makes the interwebs great. I am happy to spend money to protect my crap if it's legitimate.

[99yam40]

From what I have read all outboard motor lower unit lube has the additives to protect from water, that is what it is designed for.
just regular gear oil for car/truck differentials does not, so using even the Walmart outboard lube should give protection if changed every year and checking it during the year for water is a good idea

[DennisG01]

What I mentioned comes straight from Mercury/Mercruiser and Merc techs after returning from training. They were differentiating their "regular" gear oil from their "Hi-Perf" stuff. I do not know if/how much regular gear oil (dino oil) can deal with water intrusion - maybe it can to some degree? But they were very clear that the synthetic, Hi-Perf was absolutely superior to regular gear oil in it's ability to handle water and prevent gear damage. To a degree, of course.

IIRC, the cost difference between the two Merc gear oil is only a couple dollars, if that, per quart.

I do know that engine oil has a "W" rating... meant for boat engines. But I don't know one way or the other about standard gear oil.

[99yam40]

Rodbolt wrote some time ago how some lower units with brass bushings have a problem with synthetic ( I think that synthetic is what he was talking about).
needed to make sure the lower did not have bushings before using it

[DennisG01]

Rodbolt wrote some time ago how some lower units with brass bushings have a problem with synthetic ( I think that synthetic is what he was talking about).
needed to make sure the lower did not have bushings before using it

To some extent, yes. But whether it's synthetic or not, is not the reason. It's dependent on whether or not the gear lube is a GL4 or GL5. GL5 should not be used with softer/brass bushings. Not all synthetics are GL5. Merc's is a GL4. Volvo's is a GL5. I'm not sure of Yamaha. I BELIEVE (someone please correct me if I'm wrong) that it's the V8 Yammies that take GL5, while the others use GL4. I do know that my engine uses GL4 so I use the Merc stuff (I also have easy access to the Merc stuff, so that helps).

[99yam40]

now that you say that, that was what the discussion was about. GL4& 5

[pstephens46]

How in the hell would one know if there are brass bushings involved? Over 7 years, I think I have used everything. GL 4-5. 80 wt. Multiweights, synthetic. Walmart private label, Yamaha brand. It’s cheap. Change it frequently.

[99yam40]

well if you do not know for sure, it would be best to stick to what the manufacturer specs for you motor

[fairdeal]

well if you do not know for sure, it would be best to stick to what the manufacturer specs for you motor

the difficulty is, until fairly recently,
in neither Owners Manual nor Service Manual has Yamaha stated anything other than
"SAE #90 hypoid"

leaving open the question of whether GL5 is ok

and, as mentioned in the first post,
allowing some to wonder if perhaps only "straight weight" 90 is allowable -
and "multigrade" xxW-90 is somehow not OK

[99yam40]

well that realy sucks if the manuals do not say what should be used

[pstephens46]

Not buying the brass failure due to incorrect gear oil. Besides the one post Rod made, is there any other evidence that the oil caused the bushings to fail?

[DennisG01]

Not buying the brass failure due to incorrect gear oil. Besides the one post Rod made, is there any other evidence that the oil caused the bushings to fail?

Here's another way to look at it. You've got Rodbolt (a well trained, experienced technician for like, 140 years) telling you it's no good... and you've got the entire Merc engineering department telling you it's no good. Do you really want to makes a decision based on your "feeling" or "disbelief"?

What evidence do you have that it DOESN'T cause issues? And, by chance, if you've run GL5 in a GL4 gearcase, and it didn't cause issues... that's not evidence. A few years of doing it does not evidence make. Specific gear oil for certain systems is nothing new.

Now, that being said... I have no idea how long it would take to cause issues. I just know that there are sources much smarter than me telling not to do it. I'm certainly not willing to be a guinea pig.

[DennisG01]

Oh... I do want to add something. I am not 100% sure of this, so take it with a grain of salt. I seem to recall that this "no-no" warning goes back quite a few years. Something about the GL5 having sulfur in it to provide more wear protection. But it was the sulfur that ate away at the soft metals. AND... along with what I "sort of" remember... newer GL5 oils may use a different formulation that is safe for the softer metals. Which means, nowadays, it may actually be OK to use GL5.

But that's a lot of "if's" and "IIRC's"... I'm still going to stick with the GL4. Better safe than sorry, and there's absolutely nothing negative about using the GL4. After all, it's not like the GL4 is a poor choice - it works quite well.