Hi all at TT i,am new to this site and looking for some answers relating to overheating problem of yz250f, i,am pretty much novice to 4 stroke mx bikes and have just recently taken delivery of  yz250f which on starting at the weekend overheated after warm up idling and riding for maximum 10 mins please note during the start up and ride i do recall hearing some kind of whining noise !!! - the overheating led to the point it blew the cylinder head breather hose blew off the retaining clip and dumped coolant likewise from overflow pipe,

Not exactly sure whats happened here and by no means a four stroke expert on matter subject -  coolant air lock in radiator !!  problem with the water / coolant pump / seal bearings !!!,  could the water pump bearings / seals / impeller have failed,  - would appreciate any feedback support whom have experienced similar problems and whats the way forward to get the beast alive and ticking.

Most obviously i,am going to have to strip down water pump / check radiator, hoses etc for blockages, drain off engine oil and check condition - any of you guys experienced anything like this, thought these four bangers were reliable solid machines.

PS i,am almost sure there was residue of oil trace on the coolant that was blown out...

Advance thanks... for any support any can offer.

Thx

Edited by ghyzfbanger, 11 July 2012 - 02:34 AM.

You might very well be over-analyzing the problem.  First, liquid cooled four-strokes like to be kept moving.  If you started it and let it idle for more than a minute or so, or were poking around slowly (5 mph), it would quite likely have overheated from a simple lack of air flow.  Of course, if this was not the case, there could be another problem.  Possibly the coolant level was low when you first ran it.  The previous owner may have blown a head gasket, too.  The bike does not typically have a lot of cooling troubles other than that.

As far as the breather hose is concerned, the heating issue had nothing to do with it coming off the cam cover.  The hose may be pinched or obstructed, which would lead to a build up of crankcase pressure that would need to find a way out.