hey guys, i hope this isn't a stupid question but, should fuel from the main tanks leak into the tip tanks? i leave my tip tanks empty unless I'm on a long flight, but today during my pre flight i noticed that my tip tanks have fuel in them, im guessing from expansion because of the heat? but shouldn't it push it out the vent tubes ? is this normal? i have about 5 gals in one and around 3 in the other.
thanks

I am not sure but I think there should be a check valve in the system.

I know I parked my M5 on a slant for a day and realized that fuel from the main had transferred to the tip. That could be a real shock upon departure with an extra 66lbs moved from the inboard to the outboard lever arm of the wing.

I recently had a situation where one of my tires deflated, leaving the plane listing noticeably to starboard. When I got down to the hangar and found this, much of the fuel that used to be on the left side of the plane was now on the right and the right aux tank was full to oevrflowing through the vented cap.

Anyway, I have the mod that puts a checkvalve on the vent lines. This also T's the vent lines together so there's now only a single vent on each side. I figured the fuel got from my main tank into the aux tank via that vent line.

I have had this problem since I purchased my plane last August. After paying money and a lot of discussion, reading, etc, I have just learned to live with it. A few questions:

What year and model is your airplane?

Is there only 1 fuel vent on each wing?

If you have only 1 vent per wing, look in the access hole nearest the vent and see if there is a small canister looking object directly above and attached to the vent.

My M5 is a 1977 and I have two vent lines per side.

One tip Jeremy gave me was to leave the fuel valve on either left or right, not off or both to keep fuel from feeding from right to left or other way.

Main to Aux, continues to be an issue for me

Ditto on TomD - when parked, leave the fuel selector valve on Left or Right, not Both.

Rev412 - when you do your check valve install please post some pictures and where are you in New Hampshire?

I found a check valve in my M6 that had the ball-check spring mis-assembled. There is a service bulletin that addressed this. (#6) If you have check valves I would take them out and check....its easy to do.

MAU MAU wrote:Ditto on TomD - when parked, leave the fuel selector valve on Left or Right, not Both.

Rev412 - when you do your check valve install please post some pictures and where are you in New Hampshire?

Or OFF it will transfer there too..

Or OFF it will transfer there too..

Sorry left that out. This is the tricky part since one would think that "OFF" shuts all ports , but evidently not.