overheating problem

Flywheel · Two Stroke Sniffer Joined: 21 Jul 2004 Karma :

hi thanks for looking

i have a problem where my ns125r keeps over heating every time i open the throttle all the way.The temperature will sudenly leap form normal to almost in the red.i dont know what the problem is.The radiator is full and the cooling system has been blead.The mixture is also correct.

Does anyone have any ideas?

cheers

mr jamez · World Chat Champion Joined: 04 Aug 2003 Karma :

Well as the coolant is full and the system is bled, it can only probably be the headgasket or the water pump. Not sure of the symptoms of a buggered water pump, but I think it would get hotter quicker than that. Get the bike up to temperature, if the hoses and rad are all nice and hot then the pump is working. Is it smoking a lot? the headgasket change is a 15 minute job, and costs about £8 for a new one. You just need to take the head off, clean the areas that mate with the gasket so all traces of dirt/gasket/crap are gone. Try not to get crap in the bore. Then just put the head gasket on the right way up and facing the right way, torque the head nuts up.

I would also clean up the temperature sensor (located on top of the cylinder head) incase that is dodgy. May also be a dodgy thermostat, put it in hot water, not quite boiling, it should slowly open up.

tatters · Exxon Valdez Joined: 04 Jan 2004 Karma :

your timing could be to far advanted or retarded and this would cause over heating l had this problem on a AF1 125 were the flywheel nut came loose and the flywheel rotated on the crank (ate the bushkey), check to see if the flywheel is set correctly on the right timing mark (just take the flywheel cover off)
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Does an NSR have a thermostatic valve in it?

This is a heat sensitive valve that stops coolant circulating through the radiator until the engine reaches a certain temperature, it opens mechanically (differing metals expanding at different rates) when the temperature reaches a certain level. Most liquid cooled bikes have one in a compartment just below the radiator filler cap (although location varies) and if this was faulty, the bike would overheat very quickly. Test it by bunging it in a pan of boiling water and watching to see if it opens.

Check yer plug to make sure it isn't running lean.

Could be a blockage in the radiator? give it a run through with a flushing compound, available at most car spares places for a couple of quid.

If that is all OK, I would suspect the head gasket too.
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Odie · World Chat Champion Joined: 24 Jul 2004 Karma :

Flywheel · Two Stroke Sniffer Joined: 21 Jul 2004 Karma :

Thanks for the help

Dont think it is the head gasket as it was replaced not that long ago and i cant see ant white smoke.

I checked the plug when it started to overheat and the inside looked fine but the metal bit that the spark jumps between was green for some reason, What does this mean? i also uped the jetting just iincase but it didnt make any didfference.

Not sure if the temperature sensor is nackered will checkk that today

Odie · World Chat Champion Joined: 24 Jul 2004 Karma :

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

Supersport · Derestricted Danger Joined: 02 Jul 2004 Karma :

I'm the guy who fitted the head gasket and I can assure you that it most certainly is not leaking. The surfaces were thoroughly cleaned and properly torqued down. There is no coolant leak nor is there excessive pressure in the radiator so I'm fairly sure that the problem is not down to a head gasket leaking.
Bleeding doesn't seem to have helped so I have to consider that it might be the water pump, some restriction to flow through the radiator or more likely the thermostat sticking partially open but I haven't had a chance to look at it yet - hopefully this weekend.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Going with the above suggestions, but also a nice simple one first. Are you using too strong a mix of antifreeze / water? Had this with my RS125 and the resulting mix was too viscous for the impellor to pump round. Fine at idle / low speed, but as speed increased the temperature shot up yet the radiator stayed only just off cold.

All the best

Keith
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Supersport · Derestricted Danger Joined: 02 Jul 2004 Karma :

Just to put a new complexion on this. I have spoken to flywheel about this problem. It seems that at full throttle and fast speeds there is no overheating problem. The problem occurs when he slows down after a high speed run. Seems to me that the cooling system is depending on airflow to keep temperatures down (naturally) but can't keep up when the airflow drops. Some sort of restriction to flow might be the cause, thermostat not fully opening or radiator blockage. We'll try to sort it out at the weekend.