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Discussion Starter · #1 ·
I’m not really sure what is happening. A few months ago I had my 2020 790 serviced. After riding it I would notice coolant would be all over the front of the engine from the overflow hose. At the time the coolant was between the max and min. That had stopped once it got lower, has not happened for two months. Last night I looked and have more coolant on the engine but the coolant tank is nearly empty. I have no idea what could be causing this.
 

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Check for wetness and chalky residue at your rad hoses (usually the left one).
 

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Discussion Starter · #5 ·
Check for wetness and chalky residue at your rad hoses (usually the left one).
I have had that chalky residue on the front many times and just wipe it off and check after each ride. It had stopped for about 2 months after looking at previous pictures. Will have to ask the dealer and see what they say, this started after the “annual/9000” mile service when they filled the coolant tank after noticing it was “bone dry”

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I'm very glad someone else has brought this up. I've had multiple issues with coolant leaks on my 2020. First was DEFINTELY the actual hoses, they were leaking THROUGH the threads out the end.

Now this situation is identical to the OP. Took the bike to the dealer and he literally told me that is how the bike runs and he was not going to take it in for service. There's nothing he could do. He tried telling me that the increased backpressure of the exhaust makes it worse and that it voids warranty (dick).

However, even with the stock exhaust, it's my understanding that the coolant will drip out of the overflow tank hose and it is "normal" for this bike. I cant seem to believe it would be designed in such a way and would really like to know if someone has a solution.

Thank you all
 

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Did you have the issue and have it fixed by doing this or is this just a thought? Please let us know.

Thank you
Its from experience as a vw/audi tech.
The bottle is there to only act as a reservoir for when the cap vents. If the cap is not seated properly, or has weak spring tension, it will allow pressure with coolant into the bottle which will over-flow. When the system cools, it will suck back the remaining coolant in bottle , emptying it. A proper working cap will only vent steam from void at top of radiator when presurised and replenish when cooled bringing expansion bottle level back to normal.
You will probably also notice your fan staying on for longer trying to cool the insufficiantly pressurised boiling coolant. All the above providing your fan is working of course.
If your thermostat sticks/airlock or pump stops working, the engine will overheat before pressuring raduator/cap.
 

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Its from experience as a vw/audi tech.
The bottle is there to only act as a reservoir for when the cap vents. If the cap is not seated properly, or has weak spring tension, it will allow pressure with coolant into the bottle which will over-flow. When the system cools, it will suck back the remaining coolant in bottle , emptying it. A proper working cap will only vent steam from void at top of radiator when presurised and replenish when cooled bringing expansion bottle level back to normal.
You will probably also notice your fan staying on for longer trying to cool the insufficiantly pressurised boiling coolant. All the above providing your fan is working of course.
If your thermostat sticks/airlock or pump stops working, the engine will overheat before pressuring raduator/cap.
So maybe just purchase a replacement expansion tank cap as surly they are not expensive and give that a try.
 

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I had a coolant leak directly from the radiator cap. It would only leak on initial warm up so aggressively that I could watch, it did leak about 3-4 ounces. It was a faulty cap. This doesn't sound exactly like the O.P.'S problem hopefully it will help someone.
 

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Discussion Starter · #11 ·
I had a coolant leak directly from the radiator cap. It would only leak on initial warm up so aggressively that I could watch, it did leak about 3-4 ounces. It was a faulty cap. This doesn't sound exactly like the O.P.'S problem hopefully it will help someone.
Definitely not having that problem. Not seeing any leak on start or any dripping even. Only notice it after I get back from a ride. Has to be coming from the overflow hose no residue anywhere else other then where it’s landing on the engine of course.
 

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Definitely not having that problem. Not seeing any leak on start or any dripping even. Only notice it after I get back from a ride. Has to be coming from the overflow hose no residue anywhere else other then where it’s landing on the engine of course.
Correct. Pressure/coolant is escaping past your faulty radiator cap and filling expansion bottle when engine is hot, then flows through overflow pipe when bottle is full. When system cools again, radiator sucks back missing coolant, emptying the expansion bottle.
Replace radiator cap and refill radiator and expansion bottle to correct levels.
 

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Discussion Starter · #14 ·
Correct. Pressure/coolant is escaping past your faulty radiator cap and filling expansion bottle when engine is hot, then flows through overflow pipe when bottle is full. When system cools again, radiator sucks back missing coolant, emptying the expansion bottle.
Replace radiator cap and refill radiator and expansion bottle to correct levels.
Interesting I’ll have to order one and see what happens. I never thought of it in that way.
 

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Correct. Pressure/coolant is escaping past your faulty radiator cap and filling expansion bottle when engine is hot, then flows through overflow pipe when bottle is full. When system cools again, radiator sucks back missing coolant, emptying the expansion bottle.
Replace radiator cap and refill radiator and expansion bottle to correct levels.
I have the exact problem on a 2020 790 used bike I just got. The dealer replaced the radiator cap for the previous owner which took the bike in for this issue more than once. There is no visible leak anywhere, but still the overflow hose is messing up the engine & my right boot when riding and is hot outside. Then the coolant level shoes low.
 

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Has the cooling system been bled properly? Is the temp running at 4 bars? And radiator fan runs keeping temp at 4 bars?
 

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I had that problem until I rerouted my overflow tank hose So that it was higher than where it exited the tank. Now, it never happens.
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Has the cooling system been bled properly? Is the temp running at 4 bars? And radiator fan runs keeping temp at 4 bars?
I don’t know if the system was bled I just got the bike used with 5k miles on it. It has been to the dealer at least a couple of times about the coolant leaking issue so i assume it is. Temp & fan running normal
 
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