2017 300rr Coolant Leak ... Only During Warmup

[Jebster]

OK, I've read through many of the threads related to coolant leaks but I think what's happening on my bike is different.

On 3 occasions after starting my bike when cold I heard some sizzling and smelled coolant and could see some drips hitting the expansion chamber directly below where the thermostat is. As I continue to ride it the leaking stops.

I haven't a clue why the thermostat (as best as I can tell) would leak but ONLY before the thermostat opens (at least that's my hypothesis).

Am I crazy? I am on the verge of ditching the thermostat ASAP, getting ready to go on a ride Saturday.

No puddles on the floor while the bike sits in the garage after being ridden.

It someone has feedback - particularly if this was/is happening to you - it would be much appreciated.

Oh, BTW . . . otherwise this bike is hands-down the most smooth-but-strong, balanced, and easy to ride machine I've ever owned or ridden. VERY happy with the performance.

[NZMarkb]

Mine kept doing it during cool down
I put a silicon hose kit that deleted the thermostat and never seen another drop
I believe replacing the O ring in the housing fixes the problem but the thermostat looks cheap and crappy anyway so I was happy to ditch it
That's my 2 cents worth anyway

[Rv4Bob]

I went to silicone kit no leaks. I think it's from the expanding plastic that leaks till it warms up.
Only thing that bothers me is the little tiny plug you put on the bypass outlet, left bottom radiator.
Anybody have issues with it?
(Sorry if I jacked your thread)

[Jebster]

No worries on jacking the thread ... I'm going to snug the housing bolts a tad to see if that helps. Suggestion by the dealer. But he also suggested the silicone kit the day I bought the bike. Kinda spendy but they look great.

[bikesparky]

I replied in your switch tread about this (sorry may bad).
Have a read there.

[dirtbird]

I replied in your switch tread about this (sorry may bad).
Have a read there.

I am 'transferring' your comment and my observation in this thread.....

......

BTW you don't have a leaking thermostat housing but a stuffed O-ring in the head.
Apparently they had a batch of sh#& O-rings in the factory that start leaking after a few hours, the pressure in the system blows coolant out the weakest spot. Sometimes on a hose clip sometimes on the thermostat.
Get them to replace the O rings and it's all good if still under warranty, if not do it yourself, easy job, just done mine.
Giveaway is to start the bike with the radiator cap off, run the engine till warm and when coolant starts spitting out madly it's the O-ring!
When the o-rings are fine you just see coolant swirl and circulating in the filler opening but no geyser.

Hmmmmm....

When I received my bike, I replaced all fluids ('xcept brake fluids) before even starting the engine.
I also replaced the standard rad tubing with the silicone kit I have from past bikes.
Since then I have put on the bike about 400 kms and yesterday I checked coolant level and found it to be a little lower than normal and corrected the level.
I am 120% sure that despite riding in hot weather and slow stuff, the bike has not boiled (actually I never had a Beta 2-stroke to boil....) so I will give it a check today.
I will give it a

[bikesparky]

When I received my bike, I replaced all fluids ('xcept brake fluids) before even starting the engine.
I also replaced the standard rad tubing with the silicone kit I have from past bikes.
Since then I have put on the bike about 400 kms and yesterday I checked coolant level and found it to be a little lower than normal and corrected the level.
I am 120% sure that despite riding in hot weather and slow stuff, the bike has not boiled (actually I never had a Beta 2-stroke to boil....) so I will give it a check today.
I will give it a

I ride in hot weather but I fitted the fan kit from new, never boiled neither but the smallest O-ring (between cyl and water jacket) was definitively stuffed! My mate's 250 just done the same...
To help you out if urgent, the KTM 300 o-rings are exactly the same.
KTM part numbers are: 0770105020 for the 105x2mm and 0770078020 for the 78x2mm.
Alternatively use your local seal- bearing place and ask for these measurements o-rings in viton.

[dirtbird]

Thanks but locally I am really ok with parts!!

[GMP]

I find it extremely hard to believe a bad head oring will blow coolant almost vertical, into the frame triangle, and on the Tstat. Its the Tstat housing or a clamp.

[Leon_RR250]

36 hours after I installed the Boano silicon kit due to a leaking t-stat housing on my 16 300 and no problems at all. 96 hours in total now.