OK to use Synthetic Gear Oil in F250 LU?

[HMBJack]

I came across a nice supply of 75W-90 fully sythetic Gear oil rated GL-5.

My F250's are model year 2006 so warranty is expired.

Any issue with me using this LU Oil?

Like - might it actually cause a leak because it lubricates so well?
Being a 75W-90, verses Yamaha's straight 90 weight Gear Oil - could this cause a problem?

Thanks,

[robert graham]

The container should say, "marine lower unit oil".....the key word "marine"....has special additives for marine lower unit gear boxes.....

[99yam40]

hope Rodbolt chimes in,
I believe he has wrote before about certain gears that do not like synthetic but have no clue myself which or what there were

[HMBJack]

This is definitely for Marine use. Specifically Volvo Penta.

The question is - any reason not to use a full synthetic?

Besides of course that the outside of the bottle does not say "Yamaha" on it...

[rodbolt17]

I am not going to spend the time, but I will share what the Yamaha engineers told us.
I asked the question at a meeting at Kennasaw.
why do we have to stock two oils.
the V8 gearcase mandates the use of synthetic at the time it was the only case to require it.

what the Yamaha engineers found, and I did the hard way on a friends F50 case, is that full synthetic oil would NOT properly lubricate any BUSHINGS.


so IF and only IF your gearcase has NO bushings and ONLY bearings you can use synthetic.

what happened on the F50 after a year of running the GL5-75w-90 is it peeled out the bushing on the ID of the fwd gear.

[HMBJack]

Thank-you Rodbolt.

I'll stick with the Yamaha brand Gear Oil.