The final drive holds 10 oz of oil. Just keep filling it until it starts to seep back out and you know you have just enough.

My manual transmission Ford Ranger 5 speed takes, wait for it . . . . . . . . . . . . . automatic transmission fluid. Because its thinner than gear oil, and does the same thing. I made the mistake of putting gear oil in it and it was sluggish, it was taking to much of what little power it had to slog through the molasses of the thick oil. Im guessing that is why Honda wants you to use motor oil, makes sense to me.

I put amsoil 10/40 synth in the gear case, and i will probably never have to mess with it again.

An explanation from a moderator on a Honda SH150i forum.
He is an industrial mechanic with expertise in hydraulics, machining, and welding. He knows what he's talking about. To quote:

"Synthetic gear oil usually contains a lot of additives to stabilize the viscosity index, these additives are solvent like and may eat the seals , cause them to swell or dissolve the plasticizer in the elastomer after which the elastomer of the seal becomes brittle ,forms cracks and start to leak.
Its like soaking the seal in paint thinner.

Its a problem which also occurred with the first generations of synthetic motoroils but in motoroil this problem has been mostly cured.
In gear oil this problem is more difficult to solve although latest generation gear oil may not have this problem anymore.

However: the use of synthetic gear oil in a normal (non race)application is only beneficial on one or two points: increased interval for changing the oil and a more "flat" viscosity index meaning the oil stays better on the same level of viscosity regardless of temperature.
Point one: changing the gear oil is really not more then 3 minutes of work and one liter of oil will give you about 5 oil replacements so also on the financial side changing the gear oil is of almost no impact.
Cost and effort are so low that i change the gear oil at the same interval as motoroil.
Point two: a better viscosity index; the gearbox only has 4 gear wheels on two axles and both axles run on ball bearings.
The effect of a better viscosity index in such a small gearbox is negligibly, its not a high tech 6 speed slipper clutch gearbox and i assume you dont drive anywhere near the pole circle/Antarctica.
Above 15 degrees C the problem of thick gear oil is almost non existing

So why take the risk of broken seals?....

Throwing the bottle in the garbage is a bit over the top but next bottle you buy you may want to reconsider the perceived holy grail of synthetic oil, its not all that fabulous,there are drawbacks to synthetic motor oil."

Never doubt what Honda tells us to do in the owners manual and maintenance manual. They know what they are doing so don't try to second guess them with all of your own ideas. It will only lead to problems and costly ones at that.
Old Dave in Western Nebraska

Just a note on my drive oil experience.

My 2002 SW Service Manual recommends the Honda GN-4 10W-40 - pg 3-16 - no surprise there.

My 2002 SW has experienced vibration starting out and the corresponding plastic vibration - new belt and 16K service performed at 12K this Spring and given clean bill of health.

After reading this post of drive oil, took off covers and looked at belt and such - almost no dust inside from this years riding and all looked OK -decided to check the drive oil and it didn't look right to me [changed last year and used Honda GN-4 10W-40 - about 3k miles ago]. Drained the oil and it appeared like it had broken down - following Big Bird I used my Shell Rotella T 15W-40 JASO-MA oil for the refill.

Can't explain it but the vibration has all but disappeared and much much smoother starting out - will monitor next Spring again because riding will end shortly here. I do intend to shorten my drive oil maintenance intervals which is listed as every 2 years.

I am much happier with my SW and been riding it more than my Scarabeo now.

Rick V

Hi Rick.

Like you, my riding has now ended for the season unfortunately.
My take on your experience is that the final drive oil type/condition should really have no influence on vibration. The oil only lubricates the 2 gears transferring power 90 degrees from the clutch output shaft to the rear wheel and their bearings.
My guess is that when you disassembled the final drive covers and cleaned the belt air filter you may have moved the belt, or covers, or something that changed the belt's path so it is no longer slapping the aluminum cover case. By any chance did you take off the aluminum drive cover and remove the belt, or take apart the variator? By your description I doubt if you did, but something as simple as incorrectly tightening the belt covers by using the wrong bolt holes, or misaligning something could affect the belt slap.
BTW, I am running Rotella T6 5W-40 in both my crankcase and final drive, as well as in my lawnmower and snowblower

Big Bird,
I agree totally - changing the drive oil should not have changed anything with the clutch or belt - I did take off the aluminum drive cover to expose the belt and have done so about 4 times before - there is evidence of belt slap on the bottom of that cover and was the first time so don't know if new belt is flexing that much - I was slightly surprised that there was virtually no belt dust inside. Put everything back together as I have in the past.
Also, performed oil and filter change - replaced Castrol 10W-40 Synthetic with Valvoline 10W-40 4T Motorcycle oil which has the JASO-MA standard. The Castrol was the previous owners recommendation but always thought there was a little excessive engine noise though no oil usage. Believe the engine has quieted down a bit so happy there and about having better high rpm valve protection.

BTW, still riding here in MN - in 50's yesterday; was out last Saturday with morning temp at 30 but with sunshine. Not ready to put the scoots away just yet.

Rick V