Fuel leak when cold?

[charlie b]

OK, I tried posting this over on the UK forum too.

Few weeks ago it warmed enough for a ride. At the end I topped off the tank (I refuel on the center stand). Filled it to the neck. Temp was in low 40's. Parked the bike on the patio (covered). Left it on the center stand.

In the next week the lows were in the -10 to -20 range and highs were in the 20's. After a couple of days I noticed a fuel smell and saw a wet spot under the bike that smelled like gas. It had dripped on the center stand leg. When it warmed up there was no more leak or wet spot.

So, two possibilities that I can think of. First, the tank got cold and decreased in size enough to force some fuel out the overflow vent. Second, I have a leak that only shows up when it gets cold (dissimilar metal kind of issue).

Which is it? Or is it something else I should be worried about.

FWIW, I rode it to work today and took a 2 hr drive and it runs great and no leaks. Temps are in the 40's and 50's.

charlie

 

[CoolNT]

I doubt you have a problem. You may have inadvertently overfilled it causing the leak.

 

[oldyaler]

Maybe when you put it on the center stand some fuel sloshed out of the overflow vent, or possibly(but unlikely) a loose fuel line clamp that shows itself when the temps are really low. I wouldn't worry about it unless it happens more often.

 

[charlie b]

The bike sat for almost a week before the leak. If it was overfilled it should have leaked when I first put it up.

I may have to calculate the volume change in the tank (should be within my capability since I do that kind of stuff for a living ).

PS did a crude calculation and the volume of the tank can change by a few cubic inches with a temp swing of 60degF. Since the tank was filled up to the neck there isn't that much free space in there so the idea of the tank shrinking causing a bit of overflow is feasible.

Wish I would have popped the fill cap when it was -20

 

[taldric]

If you popped it it might have spurted fuel all over your tank! But good to know.

 

[HNT010]

I had a similar problem during winter storage - tank full. Turns out it was the gasket at the bottom of the tank and it might self heal as it turns warmer, but I think I will replace the gasket to be certain.

 

[charlie b]

Mine self healed, but, it was never that cold again while I had it so don't know if it would do it again. In regular temps (above zero ) it never leaked again.

It does not seem to be a common problem. Actually your instance and mine are the only two I have heard of and some (on the UK forum) claimed I did not know what I was talking about, ie, it couldn't happen that way.