2001 426 coolant leaking issue.

i bought a 2001 yz426f a couple weeks back. when the bike would idle stationary for to long it would drip a bit of coolant (appeared to be from the overflow atleast to me). so yesterday i rode it for the first time, pretty much all day in east san diego. at the end of the day when i pulled in, it started smoking (white) fairly badly from the front of the engine. after shutting it down when i would kick it thru with the compression pulled in, it would billow white smoke from the oil over flow line. i checked the coolant and noticed that i couldnt see any fluids in the radiator. so i mixed up some water wetter and began to pour it in. it went in and then instantly out from where the pipe (#6 in the diagram) goes into the head. after looking at the diagram i assumed that the o-ring had gone bad, so today i replaced it and it continues to do the same thing. i looked at the head and i couldnt see any crack or anything like that. any help is greatly appreciated.



The pipe may be defective, like a rust through, or something. Reinspect it. If that's not it, you may not have cleaned up the pipe or the bore well enough, or you may have damaged the O-ring.

the hole into the head is a tight spot, but i cleaned it with a tooth brush, wd 40 and a rag, i did the same on the pipe. i feel like i would have noticed a crack, in the pipe, but i'll pull it again tomorrow and check again. i put a new o-ring in today.

so i pulled it the pipe again. it appears as though there is a gouge in the inlet.


the pipe also appears to have a small dent in it, but the dent doesn't match up to where what appears to be a gouge is.


The O-ring actually seats in the outer step of that bore, but the burr in the smaller section may be pushing the tube off center far enough to leak.

alright so i fixed the gouge and built up that inside lip with some JB weld and a dremel came out well. put some wheel grease on the pipe and it seals nicely no leak now.

so everything has been drained for a while. or so i thought. is there an additional drain besides the drain at the water pump. i know on my sport bikes there is a water pump drain and a a drain for the engine its self. i drained the from the water pump like the manual says (makes no mention of an additional drain) filled with just under 5 cups of distilled water/water wetter. the manual says 1.27 qts which is just over 5 cups. as soon as i started the bike it blew quite a bit of coolant out the over flow. which leads me to believe that it wasnt fully drained. so here is my 2nd question. when the system is filled to capacity is it not to the top of the radiator? im a bit perplexed by this, but my knowledge of dirtbikes is fairly limited

The system should be filled full, but it won't stay that way. The coolant will expand with heat, and some will normally be forced out. Not much, though, and what you should end up with after the bike cools is a coolant level just above the tops of the tubes in the radiator core.

You should know that it will normally boil over within 5 minutes of being started if you don't get it moving through the air because the water pump does move very much at an idle, and there is no air flow. If it blows water sooner than that, you may have a leaking head gasket.

Is there a way to verify a leaking head gasket or other signs?

Some shops may be able to test for the presence of combustion gasses in the coolant. Otherwise, you have to analyze whether the radiator pressure rises more than the temperature increase would cause when subjected to a load.

I was able to "borrow" a unit just like the one in this link from my local Autozone:


Their loaner program is actually pretty fair. You basically pay for the tool, then you get a full refund when you bring it back.

The link has instructions for automotive applications, but there is no reason it wouldn't work on a bike. Just be sure that no engine coolant goes into the tester, because it will usually show a false positive. You only want the air (gases) to enter the tester from the radiator.

so the head gasket was blown. the head go so hot that the oil deteriorated and the cam journals on the intake came were wrecked by the cam. i got a replacement head and had the piston, cylinder gasket, head gasket and left side case gasket replaced while it was torn down. runs well now. had to change the oil 4 times to get all the water out. rode it yesterday and all seems well. im going to change the oil one more time, just to be safe.

the only odd thing that i noticed yesterday, was that after about an hr or so of trail riding, when coming back in the coolant would be about an inch or so low. it did that consistently all day, but i never noticed it dripping from the over flow.

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