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I have an M Reg 1995 Yamaha YZF 750 which has started to overheat recently. On a long run with relatively few stops the problem does not present itself with the temperature indicating around 70 degrees. If however I have to go through town or ride slowly, the temperature increases to around 95 degrees (indicated) before the bike appears to boil all the water from the expansion tank through its overboard drain pipe. I have checked the operation of the thermostat in boiling water and it does open fully, the fan does not come on when the overheating occurs but the manual does state that its operating temperature is 105 degrees plus/minus 3 degrees (the fans do operate when the connectors are shorted). Does anyone have experience of this problem with a YZF 750 or perhaps have any ideas on components I could check? Thanks.
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I think your temperature guage must me inacurate as the water is boiling under pressure, so must be way above 100c.
Your rad pressure cap could be very weak not allowing pressure to build up.
I would plump for a faulty fan temperature switch.
Try shorting the fan switch making the fan run continuously & see if you still have a problem.
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I think your temperature guage must me inacurate as the water is boiling under pressure, so must be way above 100c. Your rad pressure cap could be very weak not allowing pressure to build up. I would plump for a faulty fan temperature switch. Try shorting the fan switch making the fan run continuously & see if you still have a problem.
Exactly what I would have said !
If the pressure is not able to build the coolant will boil at a lower temp.
The fans on my FZR 600, ZX7R and ZRX1100 would all come on quite readilly in town. I would change the pressure cap AND fan temp switch.
Dont let it overheat, switch off the second it boils otherwise very expensive.
Make sure you have coolant in it, not just water, coolant has a corrosion inhibitor, antifreeze and conduct heat better than water.
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As mentioned above, plus - It's quite common for the rubber seal on the rad pressure cap to split and let things boil over.
I'd say it's not overheating, but blowing water out can cause problems shortly after.
Martin
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I agree with the suggestions above.
Cheers
DP
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Thanks very much for all the above suggestions. I should have added that I've already changed the original radiator cap for a new item due to perishing of the upper seal evident, with the problem remaining the same. However I shall look at the temperature switch and see what difference that makes. Once again thanks and I'll let you know how it goes.
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This sounds normal-ish for the YZF750R, I did 60,000 miles on mine, the cooling system is hugely efficient over 40mph, but it needs to be cos the thing boils around town, even after a short time at slow speeds. The Mersey tunnel in rush hour is a nightmare, do you switch it off, or coast downhill in neutral?, I tried them all. I'd flush the system, fill it with Kool, or similar, but don't expect much improvement. Just make sure there's no air locks.
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Put a manual switch in the coolling fan circuit.
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