Coolant overflow.

NeverLost

NeverLost

fast rider
Joined
Oct 7, 2020
Messages
74
Location
Bozeman, MT
Every time I open the radiator cap (with the bike completely cold) the coolant overflows. Maybe a lot has expanded into the overflow tank and it is still running back when I open the radiator cap for some reason?
Any tips on how to avoid this mess?
 
BISavage said:
So, just wondering, which reason is there to open the radiator cap when there is coolant inside?
Click to expand...
How do you know there is coolant in there if you don't open it? 🤷‍♂️
Actually, I was put a new, prettier cap on and wanted to check how things looked since my last ride.
 
When the tank has fluid and the bike doesnt over heat than there should be no worries?

Opening the radiator cap will always cause some to come out unless there is not enough inside, the cap is not the highest point in the system.

The cap is used to fill it up when you change fluid.
 
Hmm...it's possible my new pretty radiator cap is faulty, and isn't letting the coolant back into the radiator.
 
And have you tried pushing the spring to see if it works?

On mine, opening the cap after letting it cool down means 4 or 5 drops spill out.
 
PXL_20201022_204010775.jpg
Interesting. So ALL the fluid in the compensating tank drains out of the radiator cap opening. And if you put it back in the compensating tank, it just drains out again. So it isn't caused by pressure in the compensating tank. The hose runs higher than the tank and the radiator, so it must be siphoning.
I swear this didn't happen before.
Apparently, you can't check the radiator fluid without emptying the compensating tank?
 
The true radiator coolant level can only be checked by removing the radiator cap. Some fluid comes out when I remove mine too. The presence of fluid in the expansion tank does not mean there isn't air in the radiator. The system is daft, having to remove the side panel to see if there is fluid in the expansion tank. On other bikes (even the 701) it's easier to check coolant level.
 
Maybe have the bike on it's side stand so the cap is a bit higher. Plus pinch the tank pipe with a brake pipe clamp before opening the radiator cap?
 
Now that I have red fluid it's easy.
I shine a light under the back to light through the tank, and look from the front in the little slit and level/markings are plainly visible.
 
NeverLost said:
Apparently, you can't check the radiator fluid without emptying the compensating tank?
Click to expand...
You just need to make the front part of the hose, between the highest part and the radiator, filled with air. I was able to accomplish this last time by pinching it until the small amount came out and then it was ok.
 
Yeah but that's missing the point. If you have to change the fluid colour and then perform some kinda trick with a torch to ascertain the level, then the original design is lacking.
 
A bit off topic, but lacking... not really. As an example my ninja came with a wierd bent rear brake reservoir hose that was obtuse to the eye and made no sense. But if you unbolted the reservoir and turned the hose 180 degrees the wierd bends fit the back of the frame perfectly and tucked the reservoir up under the seat where there was mysteriously a threaded hole with nothing in it.

And in a rare coincidence there too was a slot to shine a light through so only the level indicators where visible.
 
Yeah, so I checked this out in detail. The compensating tank is higher than the the radiator, and it is vented, so no pressure builds up there. Both my original and the replacement pretty radiator cap have return valves, but they do open at atmospheric pressure. Essentially:
  • If the coolant hose between the radiator and the compensating tank is full of fluid, when you open the radiator cap all of the fluid in the compensating tank will siphon out.
  • If there is an air gap in the hose, that will prevent siphoning, because the hose runs higher than both the tank and the radiator fluid levels.
So, if you open the radiator cap and fluid starts to leak out, pinch the hose closed.
PXL_20201022_221324934.jpg

That shiny stainless steel bolt on the bottom right of the coolant tank? The original bolt was missing (or fell out) and so I put that one in. Whoops! Laughing... NO! That is where the side panel screw goes! I was chagrined when I went to screw the side panel on and found my shiny bolt in the way.
And yes, checking the fluid level in the coolant tank is a pain. But I guess a hole in the side panel was deemed too ugly by the designers. I wonder if they could have put a long neck on the tank so that it could be filled / checked from under the seat?
 
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Oh, and one other interesting finding. The factory recommends Motorex M3.0 coolant... which is PINK. And the coolant in the bike is GREEN. So I guess they don't follow their own recommendation.
I'll be replacing with engine ice next year regardless, to match my other bikes.
 
I put in Motul Factory Line and am happy with it so far; it seems to perform very differently than the stock stuff.
 

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