2010 YZ450F Oil Sightglass

So my 2010 YZ450F oil sightglass is in an odd location. I noticed it's above the the fill plug so I called the local Yamaha dealer and asked if I should be able to see oil in the sightglass while the engine is


not running and of course he said yes which confused the hell out of me..... I figured he knew what he was talking about since his job is to sell yamahas but I'm not convinced. So what's the deal


guys?? Should I be able to see the oil level when the engine is not running and how high should it be in the sightglass while the engine is running? And what's the consequences of overfilling??

Edited by cobrabrouk

Start it let it run for a minute or two, shut it off and then wait a few minutes to check it with the bike on a level stand. If you drain both the crank and the reservoir the bike will take  exactly one quart.

No you will not be able to see oil the sight glass before it is running. I had a dealer tell me the same thing when I first got my bike. I had changed the oil and put one quart in as according to manual. My buddy kept telling me you should be able to see it in the sight glass(we were at the track), I second guessed myself. So we called the local dealer.  I made the mistake of keep putting oil in until I could see it. At some point I realized seemed strange for a bike to take much more than a quart. Had to drain it back out. Seems dealers are misinformed about this.

You guys are correct. Start it and run it for a minute and shut it off.

Sight glass is in the oil tank which is higher than the crank. That is why nothing in sight glass. It all drains back into engine when it sits

Not exactly.  To begin with, it's a dry sump system:




These systems consist of a feed pump that draws oil from a tank, or in the case of the '06 and later YZ450, an internal reservoir that is separated from the crankcase.  This pump feeds oil to the vital parts, and that oil then runs down to the bottom of the crankcase (the sump) where it is picked up by a second, larger pump that quickly removes it and sends it back to the tank. 


The feed side has a low pressure check valve in it to prevent oil from draining out of the "tank" back to the bottom, but the return side does not.  The port through which the oil returns to the tank is lower on the engine than the sight glass is by about 15mm, so after you first shut the engine off, you will see the actual oil level in the glass.  But after a while, oil will have run back down the return passage, seeping past the pump rotors until it drains to the level of the return port.  That leaves oil in the tank, but none showing in the glass.

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