426 Getting way to hot/ loseing coolent

Sounds like you might have a blown head gasket. Any car repair shop that has a smog check machine can hold the tailpipe sniffer over your open radiator and if there is a lot of hydrocarbon then you have a blown head gasket.


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On two wheels (or 3) since 1970

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'99 WR/YZ400F 'Cause thumpers rule and two strokes drool!

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I can't figure out what to doo to get my radiator to stop leaking fluid out of the over flow tub. Changed the cap, messed with the jetting, the radiator keeps pres. just fine, pump works just fine. But it get too hot and the pipe looks like a light bulb in the dark. No matter if I am out running fast, slow or maxed out, still happens.

Need Help.

All YZFs will make the head pipe glow after a minute or so at idle. They all will spit coolant out the overflow. If you are filling it to the top you are overfilling it. The water needs some room to expand when it heats up. I don’t ride in tight areas so my rad.s get good airflow but if I fill to about an inch from bottom of fill inlet my 426 will not lose any coolant during a normal ride. If I fill it up it simply spits out that first inch as soon as it warms up. My cap is stock. But I don’t have an overflow container, filling a WR to the top may be an acceptable practice.

A blown head gasket that is allowing your coolant to enter combustion chamber will result in coolant disappearing (and not coming out overflow) and a grayish color to the coolant with maybe some black bubbles (HCs that MotoGreg is talking about). If you run antifreeze it also makes the exhaust smell funny.

Hope this helps, and I hope nothing is wrong with your bike (I don’t think there is).

I read a post from a guy who had a grossly mal-jetted bike, from the dealer, and it resulted in a glowing pipe during riding (as opposed to after a few minutes of idling while sitting still - which is normal). A jetting correction solved his problem. I probably saw it at dirtrider.net.


Hey Dude, I can sympathize with you!

I had overheating problems right out of the box. I tried everything to fix the problem. Nothing worked. I had to bring the bike back to the dealer and have Yammie brought in to resolve the issue.

2 Dad's Racing helped me tremendously.

Mark, after hearing all the facts, said the problem was with jetting. Although my dealer claimed it was okay, and after servicing the bike said it "didn't need to be rejetted" the bike has not overheated ( as stated in previous forum ) or has the pipe turned cherry red. Hmmmm.....

One thing I've come to learn about my 426 is riding conditions play a factor in how she performs ( to a degree ).

What is your riding situation like?

Are you MX'ing on groomed trails?

Trail riding in the woods?

I ride on loose soil, hard packed clay, rock, railroad ballast, and grass fields.

Alot of the trails I run, turn into instant mud ranging from 6" to 2 feet deep when it rains. The quad riders keep it rutted. Sometimes I have to ride in low gear ( 1st or 2nd ) to keep momentuem and traction. If she starts to bog down and really works for an extended period, my Yammie will throw the green stuff. Otherwise, no overheating problem.

I cannot say for sure it's your jetting. Im not experienced enough to nail it down, but your issue sounds a lot like mine.

I suggest you call Mark. He, like the others here, will help guide you in the right direction.

Best wishes, and if I can help, let me know.

God Bless!


YZ426 Kicks



[This message has been edited by YZ426 Kicks (edited 10-09-2000).]



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