Radiator overflow bottle.. is it safe to remove it?

I am new to the WR bikes and I just picked up a new 426. I noticed that behind the left side number plate is an overflow bottle for the radiator. My question is this.. Can I remove this and not damage the coolant system of the bike?

(I do not ride for hours at a time without stopping and not sure I would overheat the bike to begin with).

Thanks in advance.


No matter how long you ride, the fluid is going to get warm and it needs a place to go. I think this is a bad idea.

Some of the guys have removed theirs. Search the subject.

Welcome and good luck



86TT225, 98CR80, 99WR, WR timing, throttle stop trimmed, air box lid removed, White Bros head pipe, silencer and air filter. Odometer and headlight removed. Moose hand and mud guards. YZ stock tank and IMS seat. Renthal Jimmy Button "highs" and Renthal Soft half waffle grips. AMA, SETRA.

Rwitlock, I think removing it is a bad idea. Im sure that you can do with out it. Many will argue this point,and yes you can get a cap off a KX or Maico? to compensate. Why bother? If you are concerned about weight savings just skip Taco Bell this week and lose that extra pound. Good luck! Dan

Originally posted by rwhitlock:

I noticed that behind the left side number plate is an overflow bottle for the radiator. Can I remove this and not damage the coolant system of the bike?


The YZ doesn’t have the reservoir, and has the same PN radiator cap, so the answer is yes.

As long as my YZFM is moving it will not spit coolant, it is at slower speeds (and lower airflow to rad.s) that these bikes get hot. If you ditch the recovery bottle just check your coolant before each ride like I do and fill to an inch or so from the top.

Yep, I had to get used to my 2000 YZ426 spitting out some coolant if I topped it off cold. When it heats to operating temperature, it needs room to expand so the level should be about an inch below the filler....like Hick describes. I also use Waterwetter and one of those heat sink supercoolers installed behind the left side radiator. Overheating is not an issue.

I removed mine and have never had a problem. I tried other rad caps, but I am currently running one that is equivalent to stock.

The main reason I did it was to minimize the crap I had to remove to get the subframe off. My bike is dual sported with a Baja kit and between all of the wires and hoses, it was a major ordeal to get the subframe off. On my old KX it was a couple bolts and the airbox clamp and that was it. I guess I was spoiled by the ease of maintenance.

I bought my 99 400 used and it had the tank off. I ride organized trail rides, dual sport, trail ride, hare scramble, and also put up and take down arrows for enduro's. (lots of slow ridin and stoppin doin arrows)

The rad cap is stock..only once have I had to top up my rad...It wasn't down very much and I have never had any problems with the reservoir removed..I live in Ontario, Canada so the summers get pretty warm on occassion.80-90 deg. F at times in July and Aug. Thats my input...

I removed the tank and ended up putting it back on as I dual sport and at times ride slow nasty terrain. The bike would spit out about a third of its fluid on evey ride and on my garage floor. Put the tank back on and the fluid is always toped off and it uses none.

On Slow nasty long uphills my bike and those of my friends always boil the fluid into the bottle and then it goes back into the radiator. My friend with the YZ just pukes it out on these trails and then replaces it back at camp.

I kept my bottle: no spillage, no fluid to add, no worries when miles from camp and no source of water around, and of course your not puking a hazardous material all over the place.


I race desert in SoCAL and have a '00 WR 400. I have run without the overflow tank on the WR and for several years on my KLX 650. Basicaly it depends on the type of riding you do. If you do alot of starting and stopping, keep the tank on(i.e. dual sport). If you race and remember to top off the radiator fluid after every race, you can remove it. Run a slightly higher atmospheric pressure radiator cap if you go without the overflow tank.

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