98 YZ 400 OVERHEATING

On my last visit to the dunes at Pismo my I had coolant coming out the overflow hose and the engine was not very hot at the time, when I opened the radiator cap the coolant was like foam.I did not notice a loss in power as I rode slowly back to camp but I had to stop again due to overheating, it was not a hot day and the radiators were getting plenty air flow. does this sound like a head gasket or something more serious.

Thanks Micheal

if the radiator coolant is producing bubbles I think you've got oil mixing with coolant, which would be the head gasket.

My bike will overheat on occassion if I'm riding tight trails or leave it running while waiting for someone. I usually just shut it down when I stop to keep from overheating.

Does your oil look watery? If so you should probably replace the head gasket. When did you notice it?

Others, more knowledgeable than myself, might be able to give you a better diagnosis. Here's to hoping it's a head gasket and that you're catching the proble early on. :cry: :cry:

I like to take things from a simple fix first, then dive into the more complex fixes. That being said, how long has it been since you replaced your radiator cap? If it's retracting at much lower pressures, that will lead to early boils and overflow through the tube. Boiling point is determined by both temperature AND pressure. Replace the cap, change the oil (look at the oil, as said earlier) and see what happens. If your radiator didn't feel hot when you were "overheating", chances are the cap is prematurely opening. My $0.02

The easiest way to tell if it's bubbling or boiling is to test it when the engine is stone cold. Fill the radiator to the top and start it up. Now do 2 things. 1) Rev it lightly and put a light load on it, does it spit coolant while it's still cold? Also remove the radiator cap and rev it lightly, do you see a lot of bubbles while it's still cold? If yes to either of these two then it's likely you have a leak somewhere, likely the head gasget.

If it's actually boiling from temp, then yes a new radiator cap is an excellent starting point. As said above, if it's not holding pressure then the coolant will boil at a much lower temp.

Thanks for the input guys. :cry:

If it's actually boiling from temp, then yes a new radiator cap is an excellent starting point. As said above, if it's not holding pressure then the coolant will boil at a much lower temp.

what cap do I need to get? Link? More Info? :cry:

I run one from a KX500....has a higher pressure rating to prevent the early boils. Have been running it for almost 5 years now with zero problems.

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