Radiator Boil Over Normal?

I just took my WR 426 out for it's second ride. I changed the oil and filter for the second time. I let the bike idle for about 10 to 15min. to let it warm up prior to checking the oil level. The radiator boiled over spewing out of the overfill tank hose. Is this normal for the WRs if let idle for this long? it was about 45 degrees out. I loosened the nut at the head to confirm the oil was cirulating. The bike ran fine during both rides. Each ride was about an hour long w/some tight trails in 45 degree weather.

Hey Finglan.

Your manual states that idling the engine for more than 5 minutes is not good. Check it out.

My '99WR will boil the radiator if I am riding very hilly, rutted trails that require a lot of clutching. This is to be expected since you are stressing the engine in these kind of conditions.

I know our 4-strokes take a long time to warm up, but it's better to do a short warm up on choke, then putt it around a bit so that there's SOME air moving through the radiator.

You can also try "Water-Wetter" in your radiator. It's an additive that you use with water and just a little bit of anti-freeze. It is supposed to help dissipate heat better than just plain anti-freeze and water alone. I use it in everything I own, but then again I live in Arizona.

Take care,


It is my understanding that the water pump is directly associated with the trans. If the bike is not moving, the water is not circulating. The water will get very hot very quickly at idle with no cooling source.

My 01 will boil over in no time...

I believe the manual states 2 minutes running time before oil checking...

I don't wait much longer...

Thanks guys, I got distracted cleaning up the garage and lost track of time. There should be no damage from this one time deal?


2001 WR 426, WC frame guards, WC skid plate, Acerbis Rally Pro hand guards & front disc guard, DeVol Rad guards, Trail Tech computer, YZ throttle stop, air box lid removed

Probably no Damage..but As the other fellas Have stated.. 5 minutes TOPS.. Have you ever seen the Glow that Header pipe makes? LOL.. But, the combination of low waterpump speed, and no airflow through the radiators will certainly heat things up in a hurry. If you did manage to damage a Headgasket.. you Need to monitor your Oil for Water (will look foamy on the dip stick..almost like a vanilla Milk Shake).. And Watch your coolant levels closely. At least for a time.

Good luck..



The combination of cold air temp and aluminum radiators and motor are definately helpful in dissapating the heat. Your bike is probably fine. Don't freak, have a beer and save the garage cleaning for AFTER you ride. BTW make sure you don't use tap water to refill. You don't want all those minerals in your cooling system. I buy destilled water from the grocery store. That water wetter sounds like good stuff.



'00 WR 400




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