Coolant from overflow on start up

I own a 2001 YZ 250 2 stroke.Just recently when I start the bike up and let her warm up,i've noticed coolant coming out of the overflow on the radiator filler neck.I have checked the coolant level and it is not overfull.On one occasion I took the radiator cap off straight away and the coolant had frothed up.

Any suggestions would be greatly appreciated.

Cheers guys


How warm is it there? Only time Ive ever had this problem is when it got cooler out... almost like the coolant was heating up to fast or something.

I've read on here that the YZ operating coolant level is just below the filler neck....filling to the top will cause the system to purge out some coolant. I've installed a small overflow bottle so that anything pushed out will return to the system.

It sounds like you have head gasket problems, has it been worked on lately or overheated to extremes?

I agree with the head gasket statement, if it warms up the head could change shape and provide a better seal when cold, most times however the opposite is what happens.

Frothy coolant is a sign, but not a sure indication, that you have head gasket issues.

If you take the head off you can check a few things to confirm the issue.

When you remove the head check the o-rings, if they are torn or shrunk, crushed in certain areas, then that's your problem.

IF they look fine, check the head with a straight edge and make sure that the mating surface is truly flat, position the straight edge on different areas of the surface and look to see if you can fit a feeler gauge between it and the head.

Do this as well with the jug while it is off, make sure that you cannot fit any feeler gauges between your straight edge and cylinder head.

Use a quality ruler that is assured to be straight btw.

If it's warped, both parts can be removed and taken to almost any cylinder head shop and resurfaced, usually doesn't cost very much at all. Ask them to remove the least amount of material as possible, you just want it straight and flat. Usually they only take off a couple thousandths of an inch.

Thanks for the info guys.I'll do as you suggested and take the head off and start from there.


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