Lower unit oil recommendation for 250 4 stroke

[JOHNREELMAN]

what is your recommendation for lower unit lube in a 250 4 stroke.
would like to switch to some sort of synthetic.
thanks

[greasyshaft]

You should post the full model code.

[DennisG01]

I use Merc's full synthetic on every lower unit I have or work on (outboard or stern drive). It's the "Hi Performance" nomenclature. I'm not a Yamaha tech, so take this with a grain of salt, but while this gear oil can be 'overkill' for some applications (some applications don't require a synthetic), I like the margin of error that this stuff provides over 'dino' oil. The Merc synthetic (as I'm sure other brands of synthetic can) can deal with some water intrusion before ruining your gears. It's a slight bit more expensive, but when you're doing it just once a year, it seems to make sense to me.

[99yam40]

I have read as long as the lower does not have any bushings only bearings in it you can use synthetic.
I would stay with what the owners manual calls for and change as you are suppose to.

[CatCam]

I laugh everytime I see these oil related questions. Your owner's manual tells you what to use. End of discussion. Use it and Chive on.

I have yet to hear ANYONE say that my motor or lower unit failed because I used XYZ oil instead of ZYX oil. Your engine will die of "old age" before it dies from an oil related breakdown.

Just do your 100 hour oil change (4-stroke) and your annual lower unit oil change and your good to go. Exterior corrosion/ water jacket corrosion will fail your motor before an oil related failure.

[DennisG01]

Along the lines of what is being mentioned about checking your manual, I agree. But if it's like most manuals (not entirely, but for the most part, gears are gears), it will probably say something like "use hypoid 90wt gear oil". In other words, just use a good quality 90wt oil for your particular lower unit (is "GL-5" the classification?). I mentioned the synthetic Merc stuff only as an (better, possibly)) option. It works anywhere 'regular' oil can be used, as well.

In regards to never hearing a lower unit blowing up because of oil, I agree to some extent. HOWEVER, that statement is not entirely true and there have been cases of lower unit failure due to oil. I know for a fact that Mercruiser's Bravo drives MUST use the Hi-Perf stuff - if you use their regular (termed 'premium') or someone else's dino oil, you will have, at minimum, shifting problems and worse case gear failure. So, not all oil is created equal. I know we're on a Yamaha forum here, so I'm only mentioning this Mercruiser stuff as an FYI.

Now, could using 'cheap' oil like the coastal stuff cause problems? I don't know - I don't have any evidence, that I'm aware of, for that. But, for me, it's not worth the time to try and figure it out (research) to save a couple of dollars once a year.

[rodbolt17]

actually I Can tell ya a story bout a man named Bill.
I kept his F50 loaded with Volvo GL5 syn oil.
I caused the fwd gear bushing failure.
the GL5 syn oil will NOT lubricate bushings properly.
yes I did it, yea I bought old man bill a new gear case. yea I rebuilt his old one.
dam old man bill passed away just before thanksgiving.
4th very close friend I lost this year.
I am about out of friends.
I do have a rebuilt F50tlrb case for sale now.

[DennisG01]

99 and Rod - that's good info to know regarding bushings. Is there a quick way to know whether or not a particular lower unit has bushings? Would it also NOT have hypoid-cut gears? Would the manual specifically say to not use synthetic?

I looked (albeit quickly) at a few F50 (I think I picked 2004 and 2006+) manuals and it simply says 'hypoid 90wt'. Just looking for some more information (knowledge). Thanks!

[boscoe99]

Yamaha apparently does not know (or won't say) which specific lower units have yellow metal bushings and which ones don't.

Most Yam gear cases are rated for use with specification GL4 lubricant. A couple (Offshore and the V8 models) specify GL5 lubricant. The SHO specifies either GL4 or GL5.

It would appear that the higher loads seen in an Offshore and V8 gear case might necessitate the use of GL5 lubricant. All other gear cases, with the exception of the SHO, even those on the latest and greatest models, call for GL4 only.

GL5 lubricant apparently has higher load bearing properties but might be injurious to certain bushings if made from yellow metals.

This does not appear to be a mineral oil versus synthetic oil situation. It is based on the GLX specification.

From wikipedia

"GL-5 is not necessarily backward-compatible in synchro-mesh transmissions which are designed for a GL-4 oil: GL-5 has a lower coefficient of friction due to the higher concentration of EP additives over GL-4, and thus synchros can not engage as effectively. Also, transmissions which explicitly call for GL-4 oil may have been designed around this lower concentration of EP additives and thus may contain yellow metal parts which GL-5 will corrode. [1]"