Coolant overflow overheating

9 replies to this topic
  • RoughNeck3042

Posted February 24, 2013 - 06:57 PM


I just bought a 03 yz426 and I took it out a few times and then it start to spill coolant out of the overflow tube I went and got a new radiator cap for it and that didnt fix the problem so i took off the empeller to see if that would fix the problem i put it back on and the coolant stopped coming out of the overflow tube however the bike is running really hot and tends to die alot the radiator fins caught on fire so I was wondering if anyone had this happen to them or new what it might be.

  • marv02

Posted February 24, 2013 - 08:44 PM


As most 4 stroke Race Dirt bikes they dont like be rode at slow speeds they need air flowing though the radiators to keep it cool, if your stopped idling the 4 strokes will over heat very fast.

i do run engine Ice in my 426 besides that it runs cool.

When you remove the radiator cap off when cold you should see the top of the first cooling rows if you top off the radiators it will spit out what it dont need but seeing the top of the fins is normal.

The 426 is no where as bad as my KTM 560 it over heated very fast when I tryed to go riding with my Daughter it use to always over heat and boil over.

If ride lot of slow stuff you might thing of getting a WR Stator with lighting coil and use a toggle swicth to a Computer fan mounted to the radiator thats what I end up doing with the KTM or I heard others ran a battery instead of a lighting stator but finding a place to put the battery and it going dead on you is the problem.

You also could run a cacth tank for the radiator.

Edited by marv02, February 24, 2013 - 08:52 PM.

  • buzzfin

Posted February 25, 2013 - 10:07 AM


Yep, if you do any sort of slow riding, it'll overheat. I do a lot of technical woods riding, so I added a catch can from a WR and also added an aftermarket stator that powers a cooling fan mounted to my radiator. Much better.....

  • RoughNeck3042

Posted February 25, 2013 - 01:17 PM


I was just idled it in my garage for about 3 minutes and when i went back and looked at the coolant that had dried on the floor it looked like it might have some oil in it

  • grayracer513

Posted February 25, 2013 - 03:37 PM


Three minutes is about 2.4 minutes too long for the bike to idle. That's your problem.

Be sure you refill it after it belched. The system only holds 2 quarts.

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  • RoughNeck3042

Posted February 25, 2013 - 04:06 PM


Sorry if im sounding like im new to this im going to sell it and i want to make sure that im not handing someone a melon the thing im worried about is since i saw that there was oil in the coolant that it might be a bad head gasket could that be possible or am i just being an idiot?

  • grayracer513

Posted February 25, 2013 - 07:49 PM


You said there was oil in the coolant on the floor. What if the oil was there before the coolant?

Check the engine oil for coolant by checking its color. Coolant turns oil into a milky foam.

You could have a bad head gasket or not, as far as anyone knows, but you certainly can't expect a YZ426 to sit and idle for anything like 3 minutes without dumping the radiator on the ground. They need to keep moving as much as possible. If the only place it overheats is while idling, and there's no mixing of coolant and oil, don't worry about it too much.

One thing you should know before selling it is that there is no '03 YZ426. The 426 was built from '00 through '02, and the '03 was the introductory year for the 450. If you've actually got a titled '03 chassis with a 426 in it, it's an engine swap.

Now, what's this about a fire?

  • RoughNeck3042

Posted February 25, 2013 - 09:34 PM


With the bike idling that long the exhaust got so hot that the radiator fins caught on fire

  • RoughNeck3042

Posted February 28, 2013 - 11:30 AM


Thanks for all the advice i mixed up the year on the bike i finally took another look at the title and realized it was an 01 well i ended up tearing down the top end of the bike and the head gasket looked pretty used the top has never been tore down the piston needs to be clean and i found that the base gasket was bad so just to make sure my reasoning is right a bad base gasket could cause the coolant overflow? Im just going to replace all the gaskets and clean the piston up and check the rings to make sure they are good again thanks for helping out a new guy it is much appreciated

  • grayracer513

Posted March 01, 2013 - 07:40 AM


The base gasket could cause coolant overflow, but only indirectly. At the front right corner of the cylinder base is a coolant passage coming from the water pump. This is sealed by the base gasket and an O-ring. If it leaks, and the coolant level drops as a result, then overheating could take place. Beyond that, it can't cause the engine to run hot or overflow.

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