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KX250 Coolant Burning

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I just bought a 2011 Kawasaki KX250F. I left the bike idling for approx. 5-10 mins. I understand now that I wasn't supposed to do that. The coolant started leaking out for 1 minute and started burning (smoke). What could I have done to the engine? I would just like to know how severe of an issue this is. 

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With a cold engine,

remove the radiator cap and start and idle the engine

fluid circulation / some agitation is normal but,

if you see lots of air bubbles rushing to the top of the coolant, the cylinder head gasket is most likely blown.

 

Idling a 4-stroke MX race bike for too long or, slow speed trail riding will overheat the engine and risk such damage.

Edited by mlatour

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Okay. So let's assume that I see that the fluid circulation is working properly. Have I for certain damaged something or is it just a possibility? As soon as I started seeing smoke I turned it off, it was more like 10-15 seconds that it was smoking. Should I bring it in to get checked? Thanks for your help by the way.

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No you can't say for certain that it's damaged,

try the simple test I described, if you see air bubbles

then you could perform a proper cooling system compression test  with the proper tool 

to confirm or not if the head gasket is blown.

Edited by mlatour
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Okay, awesome. Thanks for the information, last question: Is the head gasket the only part that would have been affected? This is my first time owning an MX dirt bike. I just can't formulate if what I have done is really bad. 

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In general yes, 

but say in a worst case scenario, like during a race or ride where both the radiators get plugged up with mud and the engine really pushed hard.

With the engine under a load and no cooling, the mating surfaces on the cylinder head and cylinder itself could get warped due to excessive heat,

again that's a worst case scenario of overheating.

 

In your case, if you simply let the engine idle too long, the hot coolant will expand,

push the radiator cap's seal and excess coolant & steam build-up will drain out the overflow tube.

(reason why enduro & off-road specific bikes have coolant overflow/recovery tanks)

Edited by mlatour
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If you intend to slow trail ride this bike, overheating should always be taken into consideration.

Engine shut off if more than 20 seconds of idling while waiting up for someone is required.

 

It's a high performance MX race bike, not a trail bike, meant to be ridden at speed with sufficient airflow thru the radiators.

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Thank-you for this. I am trail riding this weekend and these are very helpful tips. If you have any more I would love to hear concerning trial riding. I will check the head gasket as you say as soon as I can! Thank you!

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