99 YZ400F radiator issues

While riding my YZ400F this weekend, I noticed a bit of steam coming from the botoom of my bike. Naturally, I shut the bike off and checked what was going on. I come to see that the radiator overflow tube ends right under my skid plate (under the engine and on top of the skid plate). I guess the tube leaked out some radiator fluid on the skid plate and since it was close to my engine, it steamed up

My Question is......it the radaitor overflow tube in the right location (stock one) and does anybody know how I can re-route th tube to end out with the rest of the tubes that dump out at the back of the transmission???

Also..... does anybody know the diameter of the radiator overflow tube???

Thanks for all the help!!!!!

Patrick M.

i think that is where mine is on my 99. 2 questions... were you riding slowly, if so those have a tendency to overheat. Also... what coolant are you running. i put engine ice in mine and also don't fill it up all the way. my manual say to, i was told not to. everytime i filled it all the way up, it spit a little out. fill it to just below the top and mine never spits any out.

the no air flow on those will sure make it overheat. could also be a weak rad cap. might check that too.

you could rerout it, but i remember my 400 overflowing just about evertime i rode. they are pretty tempermental to heat. i put an overflow tank off of a WR and it fit perfectly, and worked great. Check out my garage for pics

ok that all makes sense

First, I have the radiator filled to the top (where the manual says to). at this point I am running regular radiator fluid (green anti-freeze and water at a 50/50 mix)

Should I change the fliud to Engine Ice????

when you talk about having an overflow tank for a WR, what year WR's have this and would a Yamaha Dealer sell them????

one last question for everybody....

is it possible to just run pure antifreeze (green, pink, or blue)....is that what engine ice is???

thanks for everybody's help!!!!!

Patrick M.

engine ice is a pre-mixed coolant that is supposed to help the engine run cooler. not sure on the year on the wr tank, but i have been looking for one for my 400 also. the first time i really rode my 400 in some very tight trails on a hot day, she puked coolant everywhere. did a lot of reading. I put a new rad cap, flushed and filled with engine ice, and really watch my ride speed, not to slow,no air flow, and have not had any more problems with it.

if we stop for any time at all, i shut it off. oh yeah... and don't fill it all the way to the top.



I think i was going slow enough to get the engine too hot!!!!

Thanks for all of your help!!!!!

I will have to change the radiator cap, convert to engine ice and keep looking for a WR radiator overflow tank

how much does Engine Ice cost???

Patrick M.

i think it is in the 10.00 range and the bottles are 1/2 gal. i think.

1 jug did mine. not sure if there is an aftermarket cap available. the oe yamaha cap was like 30.00.

have fun


where could i find an aftermarket radiator cap???

an websites or parts companies to look for????

Patrick M.

pit posse does some, bike bandit does oe and aftermarket stuff.

pit posse seems to be quicker on shipment to me.

and of course ebay and thumper talk store

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