yz overheating???

mrbb · Apr 25, 2011

Ok I have a 2000 yz 250
I have a problem with the bike pushing out coolant , through its over flow tube,after only a short ride(15-20 min)
the bike is fine every where i can tell,( good compression, plugs are fine, run seemingly right)
I check fluid levers before runs, and after i fill to correct level, I ride, and as soon as it get hot( up to normal temp) and i rev the bike it comes out, it will then keep coming out if I just rev the bike, it will come out to the point it will drain till I stop riding
I always shut down, the level in my rad is then about 2-3 inches+ from the top(low and needing more)

any Ideas on whats going on?

thanks

mrbb · Apr 25, 2011

also, radiators are in excellent shape no dingers or bends, and all tubes/line are good as well

whenfoxforks-ruled · Apr 25, 2011

The head and cylinder connection is leaking into your coolant. Play it safe and have both checked, or just resurfaces by a professional. Have the tuner check the bore for being true/new top end. Eric Gorr or Pete Payne can fix it. Vintage Bob

mrbb · Apr 25, 2011

would there be any visual sign that can be seen by looking, as the bike ran great last year, and this is the fisrt I am out on it since winter, and it started to do this on the first ride!!
was very solid all last year before storing it for winter

I was going to do a rebuild over the winter, but lost my job so things have been tight

whenfoxforks-ruled · Apr 26, 2011

Take the radiator cap off, start the bike. You may see bubbles in the stream, as the rpm and temperature come up. Look at the spark plug, black and wet? Sometimes you can smell it, its smells sweet. Sometimes you can see it, white smoke. Rig a pressure test into the spark plug, with the piston at tdc, may show in the coolant. If you pull the head off, you may see where it has been leaking. Test your cap should be on the list first, come to think about it. It can look and run great, most times it seriously will run better than ever, right before it blows up, literally. I have read many manuals, not 1 has ever said anything about "looking" good. Take apart and inspect at regular intervals. That is measure and inspect for signs of wear. Again, parts MAY look fine, and be worn out. Start with the easy stuff like the cap, or even normal displacement of fluid. The pump can be suspect, that mixes with the tranny oil, usually. And to some it may run great, have you ever seen a steam engine?

mrbb · Apr 26, 2011

thanks for all the info
I wasn't meaning that just because it looks Ok it is
I was just wondering if there were any visual signs of the problem I should be seeing
, like leak, build up of sorts around connections
as I have none that can be seen
so I was wondering if I was missing something

as for smoke while running, No just a small amount of 2 stroke smoke and smell
no sweet or white skoke

changed the trans oil today, and it too looked like new(only have about 30 minutes on the last change) so no sign of anything getting into it from what I can see. and the plug look just fine , not wet or brown, just looks like it should, bike also idles fine, and has no knowks any where too!( I Know that doesn't mean all is well, just saying)

I am planning on taking the bike to SHOP, and having them do a look over and have them fix it if they find the problem(as long as i can affiord it, just lost my job so funds are tight)
I am never one to run things if all isn't good.
I like to think I take care of thing before they go, doing regular Pm's
But this caught me by suprise, as it was so solid before putting it away for the season!, and first ride THIS!

any way to test the water pump?

mrbb · Apr 26, 2011

Ok, did a good once over on the bike on a stand
and found that the front sprocket bolt was rubbing my case saver(had new sprockets and chain put on before I put it away)

removed the case saver
changed coolant
ran bike on stand, till it was pretty hot

no more coolant leaking out overflow

could this have been my problem
or do i still maybe have a problem?

whenfoxforks-ruled · Apr 26, 2011

I do not believe a loose bolt rubbing would cause over heating. Take the cap to an auto zone type place and ask them to test it. Some leaks happen cold, some only when hot. If it is a head leak, it will get worse and show itself. If it is the impeller, it may, only over heat under load. Did you look into the radiator while running? Take the cap off cold and start it up. Let it get warm, rev it and look for bubbles.

mrbb · Apr 26, 2011

soory, let me explain better
my case saver when the guy put on the new front sprocket, I am guessing it was thicker than the old one

as when the case saver was put back on, as you tightened the screw's it actually tightened up snug to the sprocket bolt
the case saver was tight to the bolt, actuallu suprised it allowed the bike to roll>
as I rode I ground about an 18 inch off the case saver, as the bolt cut the case saver, like a lathe!
but it still had contact with the bolt
putting a bunch of stress on it
making the bike run harder then normal to turn it!

I am not sure this is/was the problem
but I took the case saver off, ran the bike till hot, and it was good

I did run the bike with the cap off
teh fluid was bubbling like crazy
what does that mean?

thanks again
and as the sprocket turned it

mrbb · Apr 26, 2011

also if its a head leak, if I replace the o rings will that fix the problem?

whenfoxforks-ruled · Apr 27, 2011

That does sound bizarre enough to make it over heat. If that issue is fixed, so may your over heating issue. The o-rings may not be blown? Except for the bubbles in the stream, lots of tiny air bubbles that increase with the rpm, not large ones that displace the air pockets? Change the o-rings may fix it. It takes some prolonged abuse to warp a head and/or cylinder, usually. The o-ring set up is the most fussy about over heating and leaking, imo. Some front sprockets have an off set, one way sticks out more than the other?

mrbb · Apr 27, 2011

here are a few pic's of what I was talking abou, you can see the not how it has been rubbing teh case saver, and the metal build up on the case saver

whenfoxforks-ruled · Apr 27, 2011

Wrong sprocket cover? That could make a bike overheat, imo. It can over heat and not cause damage also. Many variables. I am no fan of that type of sprocket cover, the case saver is actually just a thin strip on front side of the sprocket. You name it, it gets stuck in there, and probably does make the engine run hotter also?

mrbb · Apr 27, 2011

Its the right part
as it worked fine before i had a shop replace the front sprocket prior to winter storage
I think there was a spacer on the back side to allow for clearance
I think the shop forgot to install it when they put on the new sprocket

well be at the shop this week, and ask/tell them about the issue to see what they do/say!

_JOE_ · Apr 28, 2011

Looks like your locking washer needs to be bent over that sprocket nut as well!

You can check the head for warpage with a piece of plate glass and a feeler gauge, the cylinder is a bit more tricky as you need to remove the studs. Bubbling coolant is a sure sign of leakage.

michaeltaz · Apr 28, 2011

Try a new head gasket. I had the same problem on my CR250 after it hadn't been used for a few months.
Cylinder was pressure tested, fit new radiator cap, but the moment the motor reached it operating temperature, it was blowing water and steam out of overflow hose. I then removed cylinder head and replaced the top gasket and my problem was cured. The old top gasket had marks of the blowby gases on it.

mrbb · May 26, 2011

sorry about thye delay in update
the sprocket/case saver rubbing was the issue
added a spacer to the case saver to get clearance, and problem solved(also changed to new collant that might have help as well)

as for the sprocket washer, there are 2 tabs, I only have the one bent over, as that is how it was before, and really don't see the need to bend both, odds are pretty low on getting past just one!

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