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Discussion Starter #1
I posted this over on the 959forum but they don't get nearly the amount of traffic over there and the knowledge base here has always been exceptional :) So I'll tell my story here.

MY 2016 959 I bought it this year with 2200miles. In preparation for track use I have thoroughly inspected everything and and prepped it. Occasionally after it has been sitting for a week or so it drops a little coolant. When it is on the kickstand it appears on the left side as if it is coming out of the bleed hole. I have read every thread written in English about this known issue.

Two weeks ago I was looking things over trying to figure out why. I found my reservoir was about 8oz overfilled and was surprised I could make such a stupid mistake and shrugged it off thinking I overfilled it due to the difficulty to read the reservoir level with the light colored Engine Ice. Now the bike has been on my lift for two weeks and it spewed out another small amount of coolant. This time the bike is straight up and down and the coolant ran down the right side of the motor and pooled a tiny bit on the left by the shock mount.

Back in I go looking. What I found was it was leaking at the junction of coolant line to the Vertical cylinder. Just a tiny amount that was pooling up and running down. If the bike was on its kickstand it runs right down to the weep hole and you could think that was the issue because you would see a little pool running out from there, why would look any further up the engine, right?

When I released the suspect clamp I got a substantial pressure equalization I was surprised because the bike had not been run for two weeks. Originally I thought it was under pressure and I cannot really explain that but if it was actually pulling a vacuum and I can make sense of it. I believe it is pulling air at that point which is near the highest point in the coolant system. When the bike gets hot it pushes a little coolant into the reservoir then cools down to pulls air in from the leak. More air in the system the more it heats and expands. Best I can figure I have got a poor clamp install and or a bad radiator cap. Oh yea, my radiator was about 8oz low, so it is pushing coolant out without drawing back in. Parts are ordered. The leaking junction is visible if you remove the right side fairing and the coil pack in case someone else has these symptoms. Photos below


Thoughts?
t_bare
 

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Sounds like a stuck thermostat...not much to a coolant system to fail...cap is functioning or the reservoir would not overfill...but if the thermostat is stuck shut it traps the vacuum in the engine as you have experienced...that's my assumption...just excited to be part of the knowledge base...lol

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Thermostats have a bypass or are designed to not completely shut of the system so I'd discount that theory.
 

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Ever seen inside a Ducati thermostat?
All cars have a thermostat bypass or even a small hole in the thermostat base plate.
 

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Ever seen inside a Ducati thermostat?
All cars have a thermostat bypass or even a small hole in the thermostat base plate.
I admit it doesn't make complete sense but it is still possible...a Google query of a stuck thermostat yields a supporting answer...bottom line...fluid gets out...but like a check valve doesn't get back in....there are very few scenarios that permit that outside of the cap and thermostat

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Discussion Starter #9
davy.j, do you think I got it right? Vacuum side of radiator cap not allowing coolant to return and the poor seal at vert cyclinder allowing coolant to leak out a little as it is sucking air? As bike heats up the increasing sized air bubble continues to push coolant into reservoir faster each heat cycle is what I am thinking.

This bike is beautiful but is a pain in the ass to work on.

Thanks,
t_bare
 

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Fix the leaks, bleed the system and see what happens then.
 

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Run it...if it overheats; thermostat...if not...when it cools; open the cap.....no leaks ...cap...repeat but leave the cap in place....leak? Probably cap...cap does have separate spring for vacuum and pressure so one system can work and not the other

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Ok here's a non googled answer..... straight from the top of my head.


The cap has a spring loaded rubber primary seal that sets the system pressure.
If the spring is good and the rubber seal is intact then it is ok
In the center of the rubber seal you will find a small nylon disc which can be gently lifted with a fingernail, and is held by a light spring.
This is the suck back valve from the overflow tank.
If there is any crap under this disc then it won't seal and coolant won't be drawn back into the main system from the overflow tank as the motor cools.
Lift that disc under a running tap which will flush any foreign matter from it and try things again.
There is also a rubber seal directly under the top of the cap which seals the system completely in conjunction with the disc valve to keep the coolant in and the air out.
 

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While back my 999 i was losing coolant from the overflow tank during a ride, more so when I stopped, it would just boil out! My mechanic thought overheating, Meh, he tried everything, he's not my mechanic anymore.

After much research on here I discovered the coolant cap is pressurised, I borrowed a friends cap from his 749 and B.I.N.G.O. all was good. A few euro's more and all was sorted. Worth a try I would say.

Good luck. :grin2:
 

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While back my 999 i was losing coolant from the overflow tank during a ride, more so when I stopped, it would just boil out! My mechanic thought overheating, Meh, he tried everything, he's not my mechanic anymore.

After much research on here I discovered the coolant cap is pressurised, I borrowed a friends cap from his 749 and B.I.N.G.O. all was good. A few euro's more and all was sorted. Worth a try I would say.

Good luck. :grin2:
Similar experience here (though with an dirt bike). Slow trails the bike would act like it was overheating, coolant pouring out the overflow hose, no catch tank, just dumps overboard. Trails I’ve ridden many times before at the same pace with no issues. I thought thermostat (Ktm dirt bikes actually have thermostats, most brands don’t). Changed it since it was only $40 or so. Exact same problem.

So at this point I just swapped radiator caps with a known good one from another bike in my garage and the issue was fixed! Faulty radiator cap the entire time.

So definitely worth a look in my opinion.
 

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Radiator caps do go bad, It is the least expensive and easiest thing to change, anytime you have an overheating issue just change the cap first if nothing more then to eliminate as an issue, There is really not much in cooling system to change out. Why not just start with what is easy to change.
 

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Discussion Starter #16
Radiator caps do go bad, It is the least expensive and easiest thing to change, anytime you have an overheating issue just change the cap first if nothing more then to eliminate as an issue, There is really not much in cooling system to change out. Why not just start with what is easy to change.
I am, but I'm stuck waiting for parts. Curious to see if this is correct logic. Bike has about 3000 miles.

t_bare
 

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Discussion Starter #17
I've got it all back together. Seems to be working but it only leaked after it sat for a couple of weeks, so time will tell.

t_bare
 

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I had the same mysterious leak on my '13 1199R and it went away a couple of weeks no riding and on the side stand would create a small pool of coolant on the crankcase which would spill out once the bike was upright. This was early on after the initial break-in. I've kept a close eye on everything and haven't had any issues in a while, the bike runs a proper temp and I just had the 12K service which requires a stationary run up to temp for the fan to kick in with no issues. I was quite puzzled and worried for a while and in searching through the internets these bikes are prone to the occasional drip from the weep hole with no serious issues. I still check regularly but put it down to italian character. Best of luck and keep us posted!
 

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Discussion Starter #20
What parts did you replace? Cap only?
Overheating and boiling problem gone?
I'm having a similar situation with my 2018 959 corse
I've replaced the knipex clamp on the vertical cylinder coolant nipple with an oem worm clamp that is used elsewhere in coolant system. This was a bitch to replace. I was able to see this weeping by using a small piece of blue disposable shop towel and hemostats worked through through a hole revealed when you remove the the coil pack on the right side. If I were you, I'd check for a leak but do not remove that clamp unless necessary. I also replaced the radiator cap. Ducati had superseded the cap at some point.

All seams well
t_bare
 
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