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340
Joined
4/26/2011
Location
Aledo, IL, USA
Fantasy
Edited Date/Time
2/7/2012 5:13pm
My 08 kx250f is overheating really bad. I will ride for about ten minutes in cold weather (around 35 degrees F) then the coolant starts to boil and flows from the overflow tube. I have been told its either needing a new water pump, the jetting is wrong, or it needs a new top end. Any ideas?
Another possibility is that you've developed a a head gasket leak and it's spitting coolant into the cylinder. This is less likely because you would probably notice it running significantly worse. Does it seem to be puffing a white smoke while running or suffer from popping and throttle hesitation? You could also pull the spark plug out and check it.
Due to the colder weather we've been having here, you might be a little bit lean on your jetting, but i'm going to say it's not lean enough that it should be running that hot to overheat.
Do you store the bike in a garage with heat? If not, have you checked the freezing point of your antifreeze? If the bike has gotten severely cold while sitting (or while hauling it in the back of a truck where the wind chill on the engine can be significantly lower than the outside temp) your antifreeze may have froze and caused your gaskets to crack.
I would start by taking your water pump cover off and checking out the impellar. Spin it and see how freely it turns. It should have a little bit of resitance but not excessive. Make sure none of the tines on the impellar are chipped. You should also inspect the shaft seal and then the gears that turn in coordiantion with the impellar shaft. You will need a new water pump cover gasket.
If you can't notice anything that seems obviously wrong with the impellar, I would lean more towards your top end. You could start there by doing a compression check and also a leak-down test if you have acess to that tool. Unfortunately, sometimes it's hard to detect a leak because you could still have a good amount of compression, but just a tiny hairline fracture in the gasket will cause it to leak coolant.
If you don't see anything wrong in the impellar area, I would plan on tearing down the top end to do an inspection and to at minimum replace the base and head gaskets.
The bike is in the garage in the non heated part. I will check the freezing point here shortly.
Also I had another hypothesis, if the rings were bad would that cause it to burn enough oil to not be able to cool the engine properly? I have noticed it has been low and every time I noticed i did an oil change and I know its full when I do it because I use a measuring funnel to double check. (it does not leak anywhere either)
I would lean toward a leaking head gasket. At those temps you should be able to ride forever with out any overheating!
We had a 2008 450 that blew the head gasket and it would be boiling over in just a few minuets. What happens is the hot exhaust gets into the coolant thus super heating it and then you have the exhaust gasses needing somewhere to go (extra pressure in the cooling system does not help) thus the quick boil-over etc. The bike still runs good during all of this too. Just gets smoking hot fast!!
Check your water pump impeller too, just to make sure. Sounds like a blown head gasket though....
Good luck!
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The puffs of white smoke tell me something is going on with your fuel burn. Most likely it's coolant getting into the cylinder. If you think you have a bad set of rings, it would be puffing a blueish smoke and it would smell hot due to the burnt oil. I think you need to plan on doing a top end. Replace your head and base gasket. Might as well throw a set of piston rings in there for cheap insurance if the piston and bore measure to spec still.
You still need to determine what caused the problem though. Still check you antifreeze freezing point. When you get the head and cylinder off, check the gasket surfaces for warpage or cracks. They will need to be lapped before re-installing. You probably have just worn the gaskets out due to the temperature swings.
mxtech1- since youre from around my area im going to assume you know of JPC or jackson performance? Junior and Jerry. they do the work on my brother bike and mine and they are ideticle. my brother bike used to get coolant in there to and the gaskets fixed it so i think tht would be the right remidy.
why would it burn the oil though? and yes i will add a little oil if i have to but i still only have about 4 hours for every oil change.
It is probably burning oil because you have worn piston rings or your valve seals are bad. You might consider taking the valves out and throwing in a new set of rubber valve seals. They aren't very expensive. I have valve/head tools if you need help swapping those out. That fix along with your piston rings should solve your oil consumption problem.
Don't neglect to check your water pump too! Since you'll be ordering parts get a water pump gasket so you can pull that sucker off there and make sure there's no funny business with the impellar.
Alright thanks for all the help Ill see what I can do!
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