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Yz250f Leaking Coolant

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I was out riding a couple weeks ago and I noticed my bike was getting really hot.  So I checked the radiators and they were out. So I filled them up with coolant again and I started riding and all of the coolant is dripping out of the overflow tube.  I was wondering if my radiator cap could be bad? I filled them up again and it just keeps doing the same thing and I have no clue what the problem is.  I checked my radiators and there are no holes in them.decalmx.jpg

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I was out riding a couple weeks ago and I noticed my bike was getting really hot.  So I checked the radiators and they were out. So I filled them up with coolant again and I started riding and all of the coolant is dripping out of the overflow tube.  I was wondering if my radiator cap could be bad? I filled them up again and it just keeps doing the same thing and I have no clue what the problem is.  I checked my radiators and there are no holes in them.attachicon.gifdecalmx.jpg

 Your guess sounds reasonable, maybe even likely. Your manual may tell you how to test it. If not, Search it or just buy a new cap. Check for other leaks, Yamahas sometimes have problems with water pump seals, though it would take a while to run dry.

Also check the Yamaha forum.

Nice bike.

 

Mike

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cap "could" be bad, but i doubt it

 

lack of airflow over the rads will cause it to overheat and push it out.

 

as mentioned, i would bet more on the waterpump seal being bad.  that is very typical.

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There is one other possibility, and that is the head gasket is leaking and you're pumping coolant out the exhaust pipe.

With the bike cold, remove the cap, crank the bike, and check the fluid thru the cap opening.  You should see coolant flowing.

The check is this: Rev it up with the cap off and check to see if there are bubbles coming up thru the tubes.  If so, the headgasket is leaking.

Edited by ronbuell

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Alright I have a 2006 yz250f. It's been a great bike up until the point I was riding it and someone pulled me off the track and said I was blowing coolant everywhere.. So I looked into where it was leaking and it seemed that it was coming from the overflow tube. So I took it down to my local shop and they couldn't find anything wrong with it.. Then they said that a tube that was running from the radiator to the engine had a kink in it and that was the reason it was leaking. So we got the bike bike hoping that it was fixed but nope it still is leaking from the overflow tube.. Any ideas what's going on?! And sorry if I posted this in the wrong forum

Edited by troyjones841

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You have a gasket leak somewhere. Typically a head gasket. Your sucking air into the coolant and pressurizing your cooling system.. The excess air in your cooling system is forcing coolant out the tube. I would look first at the radiator cap and replace with a known good one. Start with the easy stuff.

Edited by sndmn2
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You have a gasket leak somewhere. Typically a head gasket. Your sucking air into the coolant and pressurizing your cooling system.. The excess air in your cooling system is forcing coolant out the tube. I would look first at the radiator cap and replace with a known good one. Start with the easy stuff.

I forgot to mention that.. The shop actually replaced the cap. I was wondering maybe if the problem is because the radiators aren't getting enough air to them. I have those metal radiator guards on it and I thought that that could possibly be causing the problem. I was going to just get the oem louvers for it but not if it has nothing to do with it haha

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cap "could" be bad, but i doubt it

 

lack of airflow over the rads will cause it to overheat and push it out.

 

as mentioned, i would bet more on the waterpump seal being bad.  that is very typical.

yeah I have those metal guards protecting my radiators and i thought that maybe there isnt enough air getting to them.  Would oem louvers help at all instead of the metal guards??

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Were you by chance slow trail riding when it overheated?

 

Slow trail riding or prolonged idling will overheat your engine.

MX bikes are designed for fast pace track riding where they get a constant flow

of air thru the radiators, reason why MX bikes don't always make for good trail bikes.

Trail oriented liquid cooled bikes often have larger radiators and even a cooling fan.

 

Too frequent overheating eposides and you risk at a minimum head gasket problems

and even warping the head's mating surface if heated high enough.

 

Since it's repeating the issue, you should have your cooling system and radiator cap pressure checked,

if no external leaks are apparent apart from the overflow tube you may have a blown head gasket.

Edited by mlatour

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Were you by chance slow trail riding when it overheated?

Slow trail riding or prolonged idling will overheat your engine.

MX bikes are designed for fast pace track riding where they get a constant flow

of air thru the radiators, reason why MX bikes don't always make for good trail bikes.

Trail oriented liquid cooled bikes often have larger radiators and even a cooling fan.

Too frequent overheating eposides and you risk at a minimum head gasket problems

and even warping the head's mating surface if heated high enough.

Since it's repeating the issue, you should have your cooling system and radiator cap pressure checked,

if no external leaks are apparent apart from the overflow tube you may have a blown head gasket.

no it wasn't in the trails, I was practicing at a track

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If you noticed that it was too hot and then found it had no coolant in it I would be stripping the head and cylinder, measuring for distortion and machining them, reassemble and determine why it ran out of coolant in the first place

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Anyhow, you'll have to pressure test the whole cooling system and verify that the water pump is functional. 

Until you find the cause of this issue, the more often you start it and let it repeat this over and over, the more you risk damaging it.

Edited by mlatour

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don't mess with the cap, it won't solve your problem - they rarely fail.  Check your radiators for signs of leaking under pressure (at temperature).  This will be mud or dirt on the frame or inside the rad guard.  Also check for a slit in a hose (especially the one coming into the waterpump - it is exposed).

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Anyhow, you'll have to pressure test the whole cooling system and verify that the water pump is functional.

Until you find the cause of this issue, the more often you start it and let it repeat this over and over, the more you risk damaging it.

do you think that not having the radiator louvers could be the problem too? Cause I have those metal guards on it and I was thinking that they could just not be getting enough air and that was causing it to pump out

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No I don't think that's an issue.

 

I ran my bike with just the metal radiator guards for a couple of seasons,

(had to remove the original shrouds to them to fit).

 

Last summer I remounted the stock shrouds in front of those metal guards for even more roost protection

(which in theory creates even more air restriction) and have no cooling problems whatsoever.

 

I ride MX track's only so there is always air flow thru the radiators.

Edited by mlatour

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