VN900 dropping coolant in overflow - Kawasaki Motorcycle Forums
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post #1 of 24 (permalink) Old 05-09-2017, 06:57 AM Thread Starter
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VN900 dropping coolant in overflow

Hi, guys, I have this problem with my Vulcan and I don't know what to do. The bike will drop coolant into the overflow bottle, especially if ridden hard( for example, just 5 min doing 85-90 mph). I suspect that the summer heat will make the problem even worse, but luckily for now it's to cold here to worry about that. The thing that baffles me is that I have a pressure in the cooling system even on the cold engine, and by cold I don't mean bike sitting half an hour but 3,4 days after the last ride. When removing rad cap it will be like I opened a Coke bottle, and the amount of the coolant that went into the overflow will be exactly the same that is missing from the cooling system (if I ride it longer it will eventually leak from the overflow, of course) Another thing is, if I ride it "normal" (lets say, 60mph) it will drop very small amount of coolant into the overflow (the level will rise few mm), but after maybe an hour, when the engine has cooled down, the vacuum will draw it back to the engine and overflow level will be the same as before the ride. And when I open the rad cap there will be no pressure. Yesterday I went to test ride it and had FI light on, so I switched the bike off and on further inspection I found fan fuse was bad(also I have fair bit of the corrosion on fuse box, cleaning is in order). I have changed the radiator cap for brand new OEM, thermostat was tested and it is OK, but even riding without it has the same effect, the bike starts like new, runs fine, pulls nice, Compression is the same on both cylinders (200psi), there is no white smoke or coolant smell from the exhaust (friend has Accord coupe with bad headgasket that was burning coolant so I have seen how that looks). When the bike is cold the hoses are soft to touch (not too soft, normal), and when I start it thew became firmer as the temp rises, and stay pressurized until bike cools down (then, depending on riding style I will have either residue pressure and lots of coolant in the overflow or no pressure and coolant level normal). I also have coolant flow trough the system, when the thermostat was out could see the coolant moving nicely. And No visible bubbling in the system also. The bike is 2008, 41K miles, I had it brand new so I know what was done maintenance wise(regular oil/filter/sparkplugs change, coolant change every 2yrs, valves adjusted, on my second stator now), only mods are Cobra PC and Hypercharger with debaffled exhaust (exhaust was cut open at around 10K miles, PC and hypercharger were instilled at approx. 35K) I really appreciate any ideas anyone has, **** thing was always good to me, but now on the bring of riding season it decides to bust ma family jewels...
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post #2 of 24 (permalink) Old 05-11-2017, 04:54 AM Thread Starter
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No ideas ? OK, now I'm officially freaking out, 2 mechanics said that they don't know what could be the problem as the symptoms would point to either bad radiator cap (which is new) or head gasket, but that it's strange that no classic HG symptoms are present.
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post #3 of 24 (permalink) Old 05-12-2017, 09:26 PM
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Get a test on the cooling system to be sure there is not exhaust getting into it from a bad head gasket or cracked head. I don't remember who made the tester I used to use in the garage thirty something years ago, but any good garage should have one. It goes on in place of the radiator cap and draws gas and vapor into a fluid which changes color in the presence of carbon monoxide.
Another way is to use an exhaust gas anilyser to check the empty space at the top of the radiator for the presence of combustible gases. A reading of 50 ppm or above indicates a leak of combustion gases into the coolant.
Hopefully, that will be negative and you can look into other things.

Last edited by waldowales; 05-12-2017 at 09:31 PM.
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post #4 of 24 (permalink) Old 05-12-2017, 11:56 PM
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Are you SURE that when you open the cap and hear the Coke sound, it is pressure and not vacuum?
Pressure defies all scientific principles.
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post #5 of 24 (permalink) Old 05-15-2017, 08:20 AM Thread Starter
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@ waldowales: unfortunately, in this backwater a-hole of the world parts I don't have access to block tester, best thing I have will be leakdown tester as in a few days when I put one together. But if leakdown doesn't show anything I will order block tester online, tho.

@ sfair: Can't say I'm 100% sure about that, TBH, but I am pretty convinced it is pressure (not very scientific, sorry). Thing is, when I open the cap I get some bubbling in the overflow and little coolant spray from rad cap hole (not much because coolant level is low at that point , but more like residual coolant that was left on the cap itself or something). Also, if there is vacuum instead of the pressure , shouldn't then the coolant from the overflow move to radiator? I am mechanic by trade (sadly, I do not work in my profession so lot to learn) and I know that it shouldn't be possible for pressure to remain in the system, that is why am so confused.

Few new points, yesterday I took the bike for a spin again, wanted to recheck compression test just in case I messed something up, engine hot, 200psi both cyl, coolant level did rise few mm's, hoses were pressurized. Checked coolant leven in radiator, was missing small amount, filled it, started the bike without the cap to see if I would get fountain (friend had bad HG on his Honda and that would happen when starting it without cap), everything was fine, few air bubbles escaped, filled the rad to the brim, closed it and left the bike to idle, it was nice and hot outside, hoses were pressurized (all the same),fan kicked in, I could sense the pressure in hoses lower slightly and temp reducing (before fan hoses were to hot to hold, after it you could hold them for few seconds). let it idle more, fan kicked little later again, so that works fine. Didn't notice any bubbling in system, flow still visibly good. What I did noticed is that if I blip the throttle wide open, I will get pressure blowing in overflow, I can see bubbling inside it, but coolant level was the same, tried it few times, same result. Then I let the bike cool down and level dropped to where it was before the ride. oh, yeah, I checked the overflow hose for blockage, of course, no problem there.
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post #6 of 24 (permalink) Old 05-15-2017, 10:52 AM
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You said you got the Coke sound after sitting for 3-4 days if I understand correctly...
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post #7 of 24 (permalink) Old 05-15-2017, 02:09 PM Thread Starter
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Quote:
Originally Posted by sfair View Post
You said you got the Coke sound after sitting for 3-4 days if I understand correctly...
That is correct, sir.
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post #8 of 24 (permalink) Old 05-15-2017, 05:05 PM
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Hoses hard or soft when this Coke sound happened?
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post #9 of 24 (permalink) Old 05-15-2017, 06:47 PM
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Still sounds like head gasket or cracked head to me.
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post #10 of 24 (permalink) Old 05-17-2017, 04:50 AM Thread Starter
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Quote:
Originally Posted by sfair View Post
Hoses hard or soft when this Coke sound happened?
Soft, one couldn't tell the system is pressurized until the cap is removed.


Quote:
Originally Posted by waldowales View Post
Still sounds like head gasket or cracked head to me.
I really hope it's the HG, and not the crack. Only thing is, how to tell which cyl is bad?
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