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Discussion Starter #1
This past couple of weeks my bike has developed a weird coolant issue. After a ride out I get home and in the time it takes me to get out of my leathers a puddle of coolant about 12 inches in diameter appears under the bike. It's coming from the overflow pipe. Weird thing is this has happened about 6 times now and the coolant level hasn't dropped. It wasn't overfilled before. It sits just under half way up the expansion tank. Usually the only way a bike can "make coolant fluid" is if the head gasket leaks and oil is introduced to the water causing the level to rise.My head gasket seems fine. Maybe I have a coolant fairy filling it up when my backs turned. Any ideas?
 

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If oil was getting into the water you'd know about it, your expansion tank would look like its filled with a frothy Latte ;)

Have you checked it is coolant and not fuel? Just a thought but if you like to fill up just before you get home from your ride and you fill up stood on the bike, when its tipped over onto the side stand fuel leaks out of the overflow?
 

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Does the bike hold the correct temp when riding ?
Could be, and I stand to be corrected, the expansion/ filler cap may not be holding pressure allowing the coolant to expand. Only a thought
And in turn, would raise the coolant temp
 

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Discussion Starter #5
Bike runs at normal temp. Expansion tank level is just under half way. Expansion tank filler screw is now just turning and not undoing which I believe is a known issue and will be replaced under warranty at next service which is being done next month. I think it's still sealing as if it wasn't the coolant would boil earlier due to lack of pressure.
 

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The correct coolant "level" is very low almost empty in the expansion tank, if you keep filling up it will keep spiting it out through the overflow. My thoughts are if you can see a trace of water in the tank its fine.
 

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Discussion Starter #7
Agreed. But if it's spitting it out you would expect the level to drop until it drops enough that it stops spitting it out. My level isn't dropping thats the weird part.
 

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Discussion Starter #9
Think I've found the problem.

I couldn't figure out how I was losing fluid but the level stayed the same in the expansion tank.

Today I stripped the bike down and removed the radiator filer cap. This enabled me to see that the radiator was not full and needed topping up. This is obviously the result of losing fluid.

The radiator cap has 2 seals (upper and lower) when you fit the cap the upper seal seals the point of contact at the top of the radiator neck so no fluid leaks out of the radiator when the system is pressurised. The lower seal fits on the bottom of the neck and seals the radiator internally so no fluid is allowed to pass to the overflow hole which is connected to a tube which goes to the expansion tank.

When the system reaches a certain pressure a spring is compressed lifting the lower seal and allowing a flow of coolant to the expansion tank. When the engine is stopped the pressure decreases to a point where a vacuum is generated which opens the little valve in the centre of the radiator cap allowing coolant to flow from the expansion tank back into the radiator.
I have to surmise that there is a fault with my radiator cap and this valve isn't opening. So my bike has been filling the expansion tank up when at normal pressure but not returning fluid to the radiator when cooling down. Fluid is then escaping from the expansion tank via the overflow hose returning the expansion tank level to normal but leaving the radiator level low. So when I check the expansion tank level all looks good and I appear to be losing fluid but the level never drops.

Have removed the radiator cap and exercised both valves and they seem to be OK. Gonna take the bike out tomorrow and check the expansion tank level when hot to see if its rising and again when cold to see if it falls as it should. Then when I get home I'll check the radiator level again. I may have to replace the radiator cap if all is not well. But at least I now have an explanation for the weird fluid loss with no apparent level change.
 

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Fit a new radiator cap and all should be good.Coolant not returning to the radiator when motor cools down.Common problem with that style of cap.
 

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Discussion Starter #11
Would you believe it a new cap has to come from Italy. Nil stock in the UK.

So Took it out today. Checked level in expansion tank before leaving and just above min. Checked again as soon as I got to Bury Hill (35 miles) still just above min and no venting. Rode home and checked again. Still just above min and still no venting. Hopefully exercising both valves did the trick.
 
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