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1985 K100RS coolant leaking from under filler neck cap. Sun May 23, 2021 5:28 pm
RS Rider
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I wasn't a member here last year but this problem goes back to last year which was the first year owning/riding the bike. As you can see there is coolant escaping from underneath the filler neck cap. The threads inside the cap are wet, as are the threads on the filler neck. You can also see that the coolant gets onto the foam padding that sits on the top of the frame onto which the fuel tank rests.
I have tried two different caps and rubber seals (the large one which seals the cap to the top of the filler neck). The only thing I can think of at this point is to replace the plastic filler neck. I did inspect the filler neck last year and could not see any issues with it at all. The orifice in the filler neck for the overflow tube is not plugged. The overflow tube was new last year and it is also not plugged and I've verified that it is not getting pinched by the fuel tank.
Do I have too much coolant in the bike? I was always under the impression that with no air in the system and the bike cold the coolant level should be topped up to the bottom of the filler neck.
Anyone here seen this issue before or have some ideas?
![1985 K100RS coolant leaking from under filler neck cap. MWUrcL](https://2img.net/r/ihimizer/img924/2403/MWUrcL.jpg)
Below, the current level of coolant can be seen in the filler neck. The bike has sat overnight and is dead cold.
![1985 K100RS coolant leaking from under filler neck cap. SEeou4](https://2img.net/r/ihimizer/img922/2144/SEeou4.jpg)
Below is the sight tube on the overflow tank. The lower ink mark indicates where the coolant level was when I went for a ride yesterday and you can clearly see its current level. Both are levels on a cold engine. The top mark represents what the level was on the bike with the engine hot right after riding it yesterday.
![1985 K100RS coolant leaking from under filler neck cap. JRepOQ](https://2img.net/r/ihimizer/img923/9630/JRepOQ.jpg)
I have tried two different caps and rubber seals (the large one which seals the cap to the top of the filler neck). The only thing I can think of at this point is to replace the plastic filler neck. I did inspect the filler neck last year and could not see any issues with it at all. The orifice in the filler neck for the overflow tube is not plugged. The overflow tube was new last year and it is also not plugged and I've verified that it is not getting pinched by the fuel tank.
Do I have too much coolant in the bike? I was always under the impression that with no air in the system and the bike cold the coolant level should be topped up to the bottom of the filler neck.
Anyone here seen this issue before or have some ideas?
![1985 K100RS coolant leaking from under filler neck cap. MWUrcL](https://2img.net/r/ihimizer/img924/2403/MWUrcL.jpg)
Below, the current level of coolant can be seen in the filler neck. The bike has sat overnight and is dead cold.
![1985 K100RS coolant leaking from under filler neck cap. SEeou4](https://2img.net/r/ihimizer/img922/2144/SEeou4.jpg)
Below is the sight tube on the overflow tank. The lower ink mark indicates where the coolant level was when I went for a ride yesterday and you can clearly see its current level. Both are levels on a cold engine. The top mark represents what the level was on the bike with the engine hot right after riding it yesterday.
![1985 K100RS coolant leaking from under filler neck cap. JRepOQ](https://2img.net/r/ihimizer/img923/9630/JRepOQ.jpg)