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yz250f 2008 overheating

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i have a 2008 mod yz250f that has been blowing all the coolant out of the top tank right down to the raidiator core. i am running a fmf power bomb system a jd jetting set up and stage 1 hot cams. The engine was rebuilt 6 hours ago and have never had any issues with it overheating untill the past 2 hours. i have had the bike for a summer in the same area i am currentely having these dramas at and this is the first time it has happened. i run motle 300v 15w50 engine oil and engine ice coolant. i have flushed my raidiator core and replaced the coolant and the raidiator cap however the problem still exists. i have done a coke bottle test and there is no conpression gasses entering the coolant system. when the raidiator cap is removed and the bike is run the coolant is very turbulant so i am gessing its not my water pump as well. i never let the bike idle without the bike being in gear so its not a stationary cooking either. it is happening at rull race speed. thanx josh

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How far are you filling the radiator? If you don't have a catch bottle then you need to fill it to the top of the core. You need expansion room. Is your jetting good, not running lean?

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I'm Running a 175 witch from memory was what was in factory and is what jd recommend for the climate I'm riding in. That tank usually ran around a half inch off the fill neck however very recently it has really dropped below the core (can sway the bike and not see coolant) and this be after a half hour or so of riding. I compared my levels against a yz250f 2011 and my bikes levels were much lower.

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I guarantee you with 99.99% certainty that you're overheating because your losing fluid out of the overflow hoses whenever the bike is running. You need to replace your water pump (i.e. impeller shaft, water pump, etc.). Kept losing coolant like crazy during rides in any conditions until realizing that it was because the water pump had gone bad. The parts are cheap and replacing them is easy.

Edited by waynetrain
typo

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The engine was rebuilt 6 hours ago and have never had any issues with it overheating untill the past 2 hours.

Although you're not showing a head gasket leak at idle per you're description, I'd retorque the head bolts once agains as they have a tendency to loosen slightly after a rebuild.

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The coolant has to be going someplace. If it is not coming out the overflow, it must being going in the engine like OldNBold state.

Normal top point is just barely above the core on a YZ.

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