[BoatFixx]

Yep...
When I picked up my 21' 800 Trail Saturday, the service manager stated that they were told by CFMOTO-USA Headquarters Main Tech Advisor to the dealers to not fill REAR differential to what is considered a "normal full" that is until its just starting to spill out the fill hole. (He said, Fill Front Differential To Typical, Full)
CFMOTO advised their dealers to fill up to 3/4" of fill hole.
My dealer service manager said he was told that when REAR is filled to max that it "blows out somewhere in the system".
Well... I left it at that and intend to find out what "somewhere in the system" means as the service manager did not elaborate.

[Stovtop]

I have found that when I fill mine to "full" it seems to bleed out the overflow tube which is right above the engine and causes gear oil burning smell so now I fill just till the oil touches the threads and it doesn't puke out anymore

[NMKawierider]

I have found that when I fill mine to "full" it seems to bleed out the overflow tube which is right above the engine and causes gear oil burning smell so now I fill just till the oil touches the threads and it doesn't puke out anymore

Mine too. Next change I'm just putting in what the manual says.

[Ktown]

Okay, now that I know HOW to fil it when replacing it.

I have another question:

When, and how often, should I replaced the diff fluid? Besides the minimum recommended in the manual?

And, any suggestions on what type/brand? I will also check the How To but, since this popped up, I thought I would ask here as well.

[NMKawierider]

Okay, now that I know HOW to fil it when replacing it.

I have another question:

When, and how often, should I replaced the diff fluid? Besides the minimum recommended in the manual?

And, any suggestions on what type/brand? I will also check the How To but, since this popped up, I thought I would ask here as well.

In a normal situation..that is one operating normally and not getting water in it I would say change them twice in the first 500 miles then every thousand there after. But if there is any reason it's getting dirty faster or it gets any water in it from river-running, change then right away. For me the front is doing just fine. The last time I changes it was over 800 miles ago and it was as clean as the day I put it in and almost no metal on the plug. That was it's third change in the first 1000 miles. The rear is a different story as there is something grinding the aluminum case and filling the oil with it. It's been getting an oil change every 150-200 miles but the last two have been extended a little as I switch to 90/140 conventional. That's slowed the destruction a little.

After the first one you can use a synthetic. I used the Valvoline 75w90 at first and still do in the front. 

[Ama]

Just watched a video about this a few days ago.
The gear oil section starts about 6 minutes in.

t=818s

[BoatFixx]

Just watched a video about this a few days ago.
The gear oil section starts about 6 minutes in.

t=818s

He's spot on! sort of difficult to follow at times, but he's still got it correct. (Get off that crack! )
I can tell you stories about brand stepping on to new $350,000.00 sportfish boats and having to adjust, and repair all sorts of things that positively should've been done at the factory, and or by the dealer!