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Discussion Starter #1
Alright so here's the deal: I monitor my vital fluid levels very closely meaning pretty much before and after every ride. I have been noticing that my coolant level seems to very slowly drop over time, but not to the point where I have bothered to try and track it down. It's so minor I only need to top it off every few months or so (I'm checking the level and topping off from the expansion tank; radiator cap has not been off in months).

But today, I came back from my usual canyon ride and I quickly noticed that my coolant level was way above the full line! Normally after a ride it is just under the Full line. The bike did not overheat, but I did notice it was getting up to 225 at a stand still pretty quickly whereas usually it stabilizes around 221 or so in similar conditions.

I'm suspecting it's just a bad radiator cap that's not holding pressure, but I'm kind of suspect because I put a new cap on it just less than a year ago. Oh and today when I came back from work, the level was exactly where it was when I finished my ride, meaning none of the coolant that got pushed into the reservoir was drawn back into the radiator. Needless to say I am not riding the bike until I get this sorted. And now I'm wondering if I could have already hurt the bike running it without pressure in the system. 225 degrees and zero pressure could equal boiling :surprise: but I am running Engine Ice.

Thoughts?
 

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Okay so i'm not experienced with this directly however did some research on it..

Most coolant related issues are leaks and coolant draining which we can rule out. Sounds like your right and has to do with pressure, get the feeling it isn't anything major in terms of repair. Came across these pressure test kits from £50-£150 or If you have roadside breakdown cover, AA maybe give them a call to test the pressure only ;)

Could the rubber pipping between coolant and radiator be loose somewhere causing loss of pressure? perhaps cracked.. Hopefully nothing to do with the water pump

Last but not least, has the radiator been burped properly
 

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Discussion Starter #3
Thanks for the reply Honda rep,

I've looked at those pressure test kits as well. I'm hoping I can borrow one from a local parts store; a lot of times they rent stuff like that for no cost.

I haven't found any leaks, and yes the radiator was properly burped months ago. bike has been perfect from then until now.
 

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Discussion Starter #5
Well in my experience a radiator cap is usually not something that can be diagnosed faulty via a simple visual inspection. I will probably just buy a new cap, because I am 95% sure that is the problem, and wait to disassemble until I have the cap.

I was just wondering if anyone here has experienced these sypmtoms, or had an oem cap go bad in less than a year. Seems strange.
 

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if the gasket on the cap is compromised, it will be visibly so

if the check valve on the cap is blocked open, it will be visibly so

if the spring in the cap is compromised, it will be easy to tell.




it's a very very simple part, and going out and using your brain will get you leaps and bounds further ahead than posting online and waiting days and days for someone to tell you what to do.
 

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Discussion Starter #7
Thanks for the (slightly condescending) help.

I've had caps that leaked slightly under pressure and the gasket looked pristine, so I don't buy that first one.

Thanks for the second and third tips. Now I know what to look for.

And I haven't been waiting days and days for someone to tell me what to do lol. I've been waiting for a day off, which for me is tomorrow and the next day. Thought I might as well get some feedback in the meantime. Sorry.
 

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Maybe the issue with your leaking slightly under pressure wasn't due to the gasket. There's more to it than that


This is likely a simple problem that you have either invented in your head (likely, based on your hypochondriacal checking of everything), or something you've already diagnosed.


If it were a head gasket you'd have more indicators than just what you've described.
 

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Discussion Starter #9
Yea I'm pretty sure it's not a headgasket. I will say though, when I drained the oil a few days ago (same day as I noticed the high coolant level) the oil coming out did look a little more "brown" than usual. Or it could have just been my imagination.

Anyway, I tried to get a new cap today before work, but they didn't have any at my local dealer. Now I'm thinking just find a generic cap that has the same pressure rating (1.1 bar). Maybe even stop by the Automotive Honda dealer. They must have one...
 

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Discussion Starter #11
Because I like to have the parts ready such that I can dissasemble and immediately reassemble. Besides, I could always return the cap, or just hold onto it for a later time.

I'll be digging into it first thing tomorrow morning. Will report back on what I find. Really hoping it's just the cap.
 

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It takes 15 mins to get to the rad cap and that's if you're dogging it. These bikes come apart super easily. It's literally more work to go buy it than it is to check it
 

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Just to be clear- the fluid level is still within acceptable levels, the bike is not overheating or even getting within 20* of overheating, and everything is working fine, but your worried that everything is not perfectly the same, right?

Your overthinking. You'll know when you have a problem.
 

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Discussion Starter #14
Oh I know I have a problem, and I have a pretty good idea of what that problem is.

I'll let you know for sure tomorrow
 

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Discussion Starter #15
Radiator is full. Cap looks fine.

Where the hell could this sudden extra volume of coolant have come from!?!?

And no I'm not imagining things. The level has been between Low and Full when cold and about Full when hot for the past 2-3 months. Now it's way above Full at all times. Wtf
 

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Discussion Starter #16
Another update.

I pressure tested the radiator and it held 19 psi for over 6 seconds (from the service manual).

Next I pressure tested my cap and strangely it will not release pressure. It'll hold 25 psi and not drop. Haven't tried over 25 out of fear of breaking it or the $250 tester I loaned. I tried another cap I had laying around from NY old Miata, and that cap too did not release pressure. Now I'm doubtful of the test rig...

Thinking about just re burping the system, pulling the excess coolant from the expansion tank, and seeing what happens
 

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Discussion Starter #18 (Edited)
No. The level did not even go down at all.

So, after pressure testing everything today I siphoned out the excess coolant in the expansion tank, started the bike up and burped it the best I could. Got a couple bubbles. Went for a ride, and I noticed bubbles were coming into the expansion tank from the vacuum tube almost non stop. Eventually the bubbles stopped, and the expansion tank at this point was close to empty.

After getting home, I topped off the expansion tank and put her back together. Btw the amount I removed from the expansion tank to get it back to normal levels was the exact amount that had to go back in to bring it to normal levels after my ride. Net zero change.

So somehow a bunch of air got into my system, which took up volume in my radiator/hoses, thus forcing the excess coolant into my expansion tank. Don't know how that happened.

Sadly, after going for another ride later today, the level is again way high, and after cooling off for a bit, none of it has been pulled into the radiator!! Mother.

Somehow air is getting into the system as I ride. Praying it's not coming from the combustion chamber.
 

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Discussion Starter #19
Struggling to think of how so much air is getting into my cooling system other than it being a head gasket issue.

Bike still does not overheat, and it runs great, but every ride more coolant is pushed into expansion tank, and none is drawn back into radiator.:frown2:
 
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