Why is coolant coming from the overflow pipe

[motolink]

I have noticed on a few times after a long ride when I stop quite a bit of coolant will come from the overflow pipe.
Today when I stopped at petrol station after a 150km the coolant started running out of the overflow pipe, this time it was quite an amount. I checked the resorver and the coolant was just below the low mark so I rode on. Did another 200km and the bike sat over night.next morning I took the radiator cap off, plenty of coolant.
After the next 200km about a cup full came out of the over flow, but no more after that.
The motor does not seem to be ant hotter.
What do think is going on here, bike has done 4500km, 2011 Roadster.

 

[motolink]

I let the bike cool down and removed the cover then checked the amount of coolant in the water bottle, it was very low, so I mixed up some coolant and measured the amount it took to get the level right between the low and high mark, it took about 600 mils.
Maybe it was over full from new and once it started to push some out of the over flow it syphon affect started?

 

[Gothlander]

There is a bleed bolt on the head behind the coolant bottle. If the air is not bled out properly in can cause problems like blow back through the overflow or hotspots in the engine.

 

[motolink]

Thanks goth, thats very worthwhile checking, can you get to the bleed bolt without lifting the tank.

 

[HellFire]

If I didn't know better (Triumph would never make a mistake like this), I'd think the hoses on the coolant reservoir tank were reversed if the coolant level is below normal. But that can't happen .... right? ... right ... well ... maybe. Was the bike built on a Friday? lol

 

[Gothlander]

Thanks goth, thats very worthwhile checking, can you get to the bleed bolt without lifting the tank.

Yes, it is just above the large hose that attaches to the head via the thermostat housing. I would also check the overflow hoses as Hellfire suggests, the one from the cap goes to the bottom (of the overflow tank) and the drain hose to the top.

 

[motolink]

Yes, it is just above the large hose that attaches to the head via the thermostat housing. I would also check the overflow hoses as Hellfire suggests, the one from the cap goes to the bottom (of the overflow tank) and the drain hose to the top.

I after a short ride yesterday it did it again, pushed out about 150 mils of water to just below the low mark when cold. I found the bleed bolt, loosened it and allowed the coolant to drip out for a bit then retightened.
Checked the overflow pipes all are connected correctly.
Looking at the water bottle design, the coolant has to fill the overflow bottle before it can come out of the overflow pipe
Very strange because the motor never seems to be hot when this happens maybe the dealer will find something when I take in.
I notice the fan only runs if the motor is running, it that correct.
Planning on another ride tomorrow, see if it occurs again.

One thing I had not done was check the radiator cap, I could not pressure test it but I did take it off, could not see any problem and gave it a clean and blow out.

 

[Pedro]

I have had this happen with several different radiators the fault was found to be the cap itself ,if it is not holding pressure once the engine cooling or air cooling has stopped ,the temp will rise in the radiator and the cap will lift,allowing extra flow to the over flow bottle.

 

[motolink]

Pedro, I am thinking the same thing, this has only happened three times an 6000km so it could very well be the cap. After my ride tomorrow I will take the cap for testing next week.
I am not sure what the cap pressure should be.

 

[Pedro]

1.2 bar. 17.4 psi i think. standard.