Fuel Cap Leak

[moosebreath]

It is unseasonably cold here in the Pacific Northwest. Overnight temperatures have been in the low teens and it has been only in the low 30's during the day. I parked my J on the ramp at Hood River today after topping the tanks. I visited the museum (they have an amazing Boeing Model 40) for a couple of hours prior to departure. On initial climbout I experienced a stream of fuel vapor exiting the left tank cap, not good.

After a quick return I discovered I could rotate the fuel caps easily with them locked in place. I borrowed some tools and tightened the springs substantially on each. That solved the problem. I had carefully adjusted the caps at annual two months ago so they were easy to lock. Both have all new o rings which are still in good condition. I can only assume that the cold temperatures reduced the spring tension sealing the caps as I have not had this problem before today.

I am curious as to wheter others have experienced the sealing of their caps changing as a result of temperature excursions. Both caps had the cotter pins in place so movement of the adjusting nut could not have been the problem.

[Hank]

I've never seen that. My first annual was in July, and I've walked it into January now. Even when adjusting caps in summer weather in mid-90s, never had a problem in below freezing temps (coldest departure was 8°F).

Happy New Year, real soon now, and good luck!

[DonMuncy]

There is a fine line between "loose enough to latch" and "tight enough to seal well". I have found that tightening the nut one cotter pin hole at a time to where you just can't work the latch mechanism and them backing off one hole, makes them nice and snug.

Bear in mind I am not an A&P or expert. There are possibly other problems that I am not aware of.

[Guest]

Check SB M20-229A, did you replace the two inner "o" rings as well or just the outer two?

Clarence

[scottfromiowa]

My problem with fuel caps is when line guys slightly cock the cap and lock it closed. I have to get a screw driver to gently pry the cap closure up. It happens a LOT...

Because it is not flush it could probably collect/get water in tank too...

[OR75]

My problem with fuel caps is when line guys slightly cock the cap and lock it closed. I have to get a screw driver to gently pry the cap closure up. It happens a LOT...

Because it is not flush it could probably collect/get water in tank too...

That's why I always open and close the locks myself