Originally Posted by Monolith (Post 216861)

Hi Folks,

Yesterday I noticed the Water Coolant warning indicator come on (red) while riding around town. approximately 5 mins the warning indicator light turned off.

Today I removed the housing protecting the coolant header tank: the levels seem okay (full) and the colour of the coolant matches that of the refill bottle I have.

I started up the bike and left it running for about 5 mins with the header tank cap off. The heat radiating from the engine, coolant hoses and radiator was hot, but i was unable to see any movement (flow) in the header tank, as one would see with a Cars' Header tank.

Is there any possibility to produce the effect of water flowing, so as to see if there is any fault or obstruction and to see if coolant is circulating through the system properly?

Could there be an Air bubble or some pump not working?

Thanks in advance.

Kind regards,

Originally Posted by Pleiades (Post 216863)

Firstly, there is no coolant flow in the expansion tank on the XT�s cooling system. It is not really a header tank at all (as it sits below the coolant level) and it is not within the pressurised part of the cooling system (and why it only has a rubber bung). It is literally there just to collect the overflow of coolant forced out when the radiator cap�s valve opens under pressure due to the volume of coolant expanding when the engine gets up to normal operating temperature. When the engine cools a vacuum is created in the pressurised part of the system sucking back the same amount of coolant that was expelled when the bike reached operating temperature. The level in the expansion tank will rise on a warm engine and fall back when cold. It should always return to the same level on a cold engine if there are no leaks in the system and the radiator cap is working properly.

This is why you should really check the coolant level in the radiator; don�t rely on the level in the expansion tank. Theoretically the expansion tank could appear full, but there may be a big air gap at the top of the radiator. Remember it�s not a header tank; what you put in the tank isn�t going to fill the radiator. Unscrew the rad cap and check the level is up to the neck. It�s quite tricky to do on a Z as the tank is very close but I find a small mirror helps to get a look inside the radiator filler neck.

Your problem could well be a radiator cap that has a weak spring, bad seal or is opening too early and not holding pressure. It should maintain a system pressure of 1.2bar (17psi). If it doesn�t, then the coolant temperature will rise much more quickly than normal and the coolant will boil at close to 100C, rather than nearer 115C when under pressure. This may explain why the temperature warning lamp is coming on early. There have been a lot of documented problems with weak or failed radiator caps on XTs, so I�d have a look here next (after having checked the coolant level in the rad.) Yamaha changed the cap design in 2010, so if you have an earlier one � be a little suspicious.

Also check the radiator fins are free from crud and that the fan is operating correctly � it should be cutting in before the temperature warning light does.

Of course all the above suggestions are based on the fact you have no obvious physical coolant leaks (as you didn�t mention any) and there is no coolant dripping out of the tell-tale on the base of the water pump housing?

Originally Posted by Monolith (Post 216868)

There does not seem to be any leaks detectable. So, it seems from your perspective, that I will need to examine further up the system to the radiator itself.

Originally Posted by Monolith (Post 216868)

i was of the opinion (unlearned in the field of Motorbike Mechanics) that the coolant 'reservoir' was where you would top up the coolant and check the levels, and from that point the coolant would circulate through the system.

Originally Posted by Monolith (Post 216868)

Could it be a false-positive, due to a temporal fault with a sensor?
or is their further testing recommended?

Any suggest a reliable meter monitor to watch the temperatures of critical systems, some thing that isn't took expensive