Not sure if this part is missing? 03 WR450F Newly aquired bike.

Do I need this part on my bike? It's not there. There seems to be 2 tapped holes where it should sit, but not sure about the hose from the radiators.



It is the radiator overflow bottle. It attaches to a fitting on the top of one of the radiators (rider's left I think, without checking) using vinyl tubing. Great help for slow, low gear riding. I wouldn't think of riding without it.

I wouldn't ride with out it. You wouldn't take the coolant overflow off your car or truck would you? Hope not.

Not sure why someone would take it out. I'm assuming it has a different type of radiator cap too so it blocks that overflow port?

Once the coolant builds so much pressure the radiator cap lets coolant through and feeds into the overflow.

Does opposite to, pulls coolant back into the radiator as it looses pressure (cools down)

Awesome thanks guys I'll take a closer look for the hose and see how the bike goes.

Not sure why someone would take it out. I'm assuming it has a different type of radiator cap too so it blocks that overflow port?

I'm not sure on all years but I believe the yz doesn't come with the overflow bottle. The wr does but I don't think it's necessary... It's nice to have if your worried about boiling over in slow trails and such but I know a few guys that have removed it on their wrs. But they're all on 99-2001s.

Yeah I think it's been removed on purpose. I seen in the service manual the overflow mounts are on the aluminum subframe, rear left.. The bike runs fun without it, no loss of coolant or anything.

If the bike is jetted properly and has a non-stock exahust, you will probably never need it. 


I never have.


You do want to route the overflow tube so it drips on the header, so you will see steam if it is overflowing.

thanks guys, i think i will leave it as is, the overflow hose is routed down under the left side of the frame just before the gear shifter..

The catch tank is there to "catch" any over flow due to slow speed over heating.  If you're on a particularly long and arduous ride, you might begin to really appreciate that catch tank if your bike starts to overheat and dump coolant back into the tank.  Without the catch tank, it goes on the ground and once it's out, it's gone!  But with the tank on, if you notice it's overheating enough to put hot coolant into the tank, you can always stop for 30 to 60 minutes (just a guess) and let everything cool enough to draw coolant back into the radiators.  That's what it's designed for anyway.  Or you could sacrifice your drinking water and hope you don't need it later.  But in the long run, it's up to you  to decide what kind of riding you're going to do and if that catch tank will serve you or not.  If you're 80 mi. from BFE, that cool-down and ensuing coolant replenishment could be the difference between you sleeping in your own bed that night or freezing to death in the high desert.  Your call.

Put on a 1.6 bar radiator cap and it won't boil at 225 degrees anymore, it will go up to 260, and usually never boil over.

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