overheating YZ 426???

7 replies to this topic
  • jecole360

Posted September 04, 2010 - 07:24 PM


I have on 02 YZ426. When I was riding it last weekend in the woods on some pretty tight trails I noticed coolant was coming out of the tube that runs down the side of the frame. When I noticed it I had ridden it to my jeep and had it leaned up against a tree while I was getting my goggles out of my jeep with it still running. Is that normal or do I have an underlying problem that I don't know about?

  • kx250fnick

Posted September 04, 2010 - 07:51 PM


I wouldn't say its normal,its just hot check your coolant levels frequently,check your rad shrouds and vents to see if they are not bent if they are bent,they need replaced to maintain cooling during riding or running conditions.

  • grayracer513

Posted September 04, 2010 - 08:29 PM


It is actually pretty typical of the YZF, particularly the 400 and 426, to boil over at very low speeds or after idling for more than 30-90 seconds. But it's a good idea to check the basics. Be sure the radiators are clean (both inside and out) and flow freely. Have the cap tested to see if it holds its rated pressure, and be sure the coolant is fresh and mixed at the right ratio.

Generally, if a YZ426 will do a full day of open riding at speeds over 10 mph without the coolant level dipping below the tops of the radiator tubes (checked after it cools off), it's pretty normal.

If you verify that and still have trouble with coolant loss because you ride a lot of tight, slow technical stuff, you can consider a battery powered fan kit, a coolant recovery system, and/or one of the "boil proof" off-road racing coolants like Evans or Zip-Ty.

  • Ryan426

Posted September 05, 2010 - 10:37 AM


like gray said, very typical of the 426. mine does it when I ride slow. what I do is get on the throttle to cool down the motor.

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  • Florida_426

Posted September 05, 2010 - 04:34 PM


Gray's points are correct, as usual. I went to a Boyessen impeller and housing for my '02 after boiling over on the starting line in Houston back in '02. While riding I have had no problems but when sitting on the line it gets warm fast. I use Hondaline coolant and distilled water at a 50%/50% mixture. No problems since and I am a pretty slow racer, admittedly and I weigh 217# so I can strain a cooling system.:bonk:

Grayracer, how often would you recommend changing out the cooling system's hoses? I check them before every ride and during each maintenance session now. I'd appreciate your thoughts.


  • grayracer513

Posted September 05, 2010 - 07:32 PM


The hoses don't get the same abuse out in the open as they do locked up under a car's hood, surrounded by 300 degree air, but you should make a habit of inspecting them, and replace them if they start to feel significantly harder or softer than normal, show any bulging, or any other deterioration to their general condition.

I don't know that it's really possible to assign a particular time interval to replacing them because of how differently each bike gets used, but they certainly warrant being among the things that get looked at regularly.

  • Florida_426

Posted September 06, 2010 - 03:09 PM


Thanks for the input, I appreciate it and sorry for the hijack of this thread.


  • FlashGordon

Posted September 06, 2010 - 07:14 PM


Go to mrcycles and buy the overflow bottle, cap and cap washer for the WR, and install it under the the left rear number plate. Will require some grinding of the plastic, and fabrication of some clamps, but you will never lose your coolant again. Keep the bottle about 1/3 full. Engine Ice is a good coolant that I prefer.

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