Honda Dirt Bikes Forum

Well - it's not boiling over, and it certainly is bripping from the overflow. I'd say it still could be a bad cap.. I'm gonna have to think on this one - I'm a bit stumped.  The video confirmed everything you were saying though.  Hmmm...  
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Here we go again!

The only way water can get out that tube is through or around that cap.  Maybe its not the cap but the part of the radiator that seals against the cap.  

Bill H. 2000 CR250R

how much pressure should be in the radiator cause it sounds like there is alot of pressure. In the video the bike was only running for 5 minutes just warming up and it has an extreme amount of pressure.(unless its supposed to do that idk)  

It would only have extreme pressure if it was boiling HOT or if the hoses were clogged/pump had failed.  You can take the cap to an auto-parts store and have it pressure tested as well!  
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Here we go again!

i had the same problem out of my 1989 cr250 i changed caps twice checked oil and put a new high comp head gasket on it . finally had to put  just a stock head gasket on mine to fix it . it would hold compression in radiators like that for days . also if the thing is overflowing because of a bad cap it will not have that much pressure in radiators . hope this helps  

I have the same problem!
i will start my bike and it will run fine, i will ride for 10 minutes not floggin it just puttin round, still hitting band but, but as soon as i hold it flat and go through the gears or as soon as the  engine heats upp good it will leak out coolant. Im running 60% coolant, 40% water.
The problem cant be with the head gasket because i just replaced that because it blew and coolant went all through my crank. It cant be the cap because i just bought a new 1 of them. It cant be blocked hoses cause i checked all the and my radiator does not have any cracks as i had it pressure tested.
I had an O-ring under the cap once and it did not leak but all my hoses got bloated and became double the size. I also checked my water pump, thats fine.
The only thing i can think of is that my radiators r full of gunk and i need the get some radiator flush.
any ideas guys?
soz for the long post.

Daniell.  

welcome to the board stash
start a new thread if you want to have more ppl see/answer you  
i eat the desert and the dessert

84HondaRider:
how much pressure should be in the radiator cause it sounds like there is alot of pressure. In the video the bike was only running for 5 minutes just warming up and it has an extreme amount of pressure.(unless its supposed to do that idk)

you have combustion pressure leaking into the cooling system. the fact that there was an obvious pressure relief when you removed the cap does not exclude the cap as a suspect (the fact that you borrowed known good caps from other machines does) and the sealing surface in the radiator (if dammaged would hold little if any pressure) seems fine. i am not an expert on mid 80's cr's but im sure the head gasket was the old style (non o-ring)style which compresses when the head bolts/nuts are torqued.

combustion pressure is causing the cooling system pressure to overcome the relief pressure of the cap.

the only area of the engine that can produce that much pressure that rapidly is in the cyl head area.

remove the head and cyl, remove any studs and clean. check the head and cyl for ANY warpage or pitting at all. if there is any doubt as to whether both surfaces are PERFECTLY FLAT have them checked at a machine shop and machined as needed.
be sure to use a NEW head gasket and follow the proper torque sequence during reassembly. make sure to check the head and cyl for any cracks.  

          post count means nothing
06yz125,kx60(2)

I agree with MJP.  

Bill H. 2000 CR250R

aye. i just saw this thread. to check for warpae you can lay the cylinder head on a sheet of glass. like a glass table or what have you. glass is hard and flat enough to indicate a warped head ussually. ~pat  
life's a garden, dig it

i fixed it!
i took the head off n checked the head gasket. it looked like all the paint had melted off.
i swent to the shop and got a new head gastket and put it back together and tightened the bolts with a torque wrench.
i dont think the bolts were tight eneough?
thanks!  

Good to hear. Just don't overtighten them.  Stripped studs can be a pain to replace.  

Bill H. 2000 CR250R