Unusual problem

[WintrSol]

After filling the fuel tanks on the way home, which was also after a fairly long ride (>50 miles), I noticed some drops of coolant next to the radiator cap, so removed the side cover; the return bottle was way over-filled, and I know I filled it properly the last time I replaced the coolant.
So, I let it cool, then removed the radiator cap, only to find the level below the top of the fins. From this I deduced that, when I re-installed either the air pump for the Goldwing air suspension, or the main fuel tank, that I managed to pinch the coolant line between the bottle and radiator. I siphoned coolant from the bottle and poured it back into the radiator, and thought I'd ride it, and repeat. Then I realized how much pressure must have built up, so to avoid blowing out part of the cooling system, it's time to find out.
Now, I have to drain the tanks by running the fuel pump, which is a bit over 8 gallons total, so I can dig into the plumbing.
Given the 'special' equipment added to the bike, this problem may be unique, but still, something to check on.

[98valk]

just drain the overflow to below the low level mark. ride it to operating temp and then let bike cool. then whatever the overflow level is fix that to where it should be per manual.
all filling should be through the overflow bottle and never the rad cap, unless a complete change it being done.
I installed evans cooling over 20 yrs ago. zero issues all of this time.

[WintrSol]

But from the results, the radiator forced coolant into the bottle, which did not return when it cooled. The hose must be pinched, as, with the radiator cap off, putting pressure on the bottle did not force coolant back, like there is a pinch point that takes a lot of pressure before coolant will flow. I think the drops of coolant near the cap was from that pressure pushing coolant out between the tubing and the overflow pipe. I did say the radiator level was too low to see, remember, when I know I filled it properly a few months ago when I drained and refilled the coolant.

[Willow]

Would an air leak at the radiator cap cause this?

Flow from the radiator is activated merely by fluid level while movement to the radiator is depending upon suction resulting from reduced fluid level.  Suction needs a completely closed system.   

[Itinifni]

A quick question, how did you apply pressure to the overflow bottle? I ask because the bottle should be vented, if the vent was not plugged the pressure would simply escape through the vent.

Also, the radiator cap effectively has two valves, one for pressure and one for vacuum. The pressure valve is obviously working as coolant went to the bottle. I have seen the vacuum valve stuck on cars leading to coolant not returning to the radiator. Usually you'll see collapsed radiator hoses due to the vacuum in the coolant system after the engine cools.

Of course this doesn't explain the drops of coolant near the radiator cap.

How about disconnecting the overflow hose from the bottle and with the cap off use a mityvac to apply vacuum to the hose? If you can build any vacuum in the hose you have a restriction.

Another possibility is the overflow hose had deteriorated with age or chemical contamination and is collapsing under vacuum creating a restriction or possibly a pin hole leading to both a small leak under pressure or venting the vacuum needed to draw coolant back to the radiator. The later could be tested with the mityvac and described above but disconnect and plug the hose at the radiator neck. Apply a very low vacuum and see if it holds.

Just throwing out ideas here.

Quick edit:
I can imagine Willow's idea of a very small leak at the radiator cap (possibly even contamination/debris on the seal) causing both the coolant leak and the coolant not returning back to the radiator.
Pressure is relatively high opening the valve to release coolant to the overflow, the vacuum builds up very slowly as the engine cools to draw it back to the radiator.

[WintrSol]

Flow to the bottle happens after pressure rises in the cooling system to that of the pressure relief value of the cap, due to expansion of the coolant from heat. When the system cools, the (small) vacuum created should draw the coolant back from the bottle through the one-way valve in the cap. That didn't happen; the level in the bottle rose, and did not return. I tested the cap, and that valve works just fine, without sticking. The end result was an empty space in the top of the radiator when I removed the cap, presumably releasing the greater-than-normal vacuum. Yes, I put pressure on the bottle, with the cap off, in hopes of returning the coolant to the radiator, but none did, indicating the blockage would take more pressure than I was willing to apply. It also indicates that it took some pressure from the radiator to force the coolant past the blockage, then, on cooling, the vacuum was more than the minimal value normally required. I think the total I drew out of the bottle to return to the radiator was about a pint to a quart, but I didn't actually measure it.

I just finished using the fuel pump to empty the tanks, so I can remove the main tank, and find the pinch point(s), which I will do tomorrow.

I posted to let folks here know that it is possible to create this condition, if the hose can be pinched in a 'normal' configuration.

[pancho]

Had a similar problem a few years back. the coolant overflow line had pinched where it runs around the neck of the frame. 

[WintrSol]

After taking the tank and air box off, I found nothing, so pulled the coolant bottle again. Opened the overflow at the radiator and blew into it - no problem with air out the bottle end. Reattached the bottle, cap on, and tried again - no flow; cap off, no problem. Took the coolant bottle overflow off, put the cap on, and again no problem. Turns out something had crawled into the coolant bottle overflow tube, blocking it. I ran a wire through it then blew into it, and some bits came out, then it blew open and clear.
I can only assume that the coolant-displaced air in the bottle was forced out around the cap, but the cap clammed up when the radiator tried to take it back.

Now to put it all back together, and ride. Tomorrow.

[Valker]

Good find. Thanks for the follow up.

[WintrSol]

All that work, and it was probably just a spider where it didn't belong. But, that means it can happen to any of us.