Just installed a new Lh bladder and at the same time installed the McFarland vent tube. My AME set the tube as per Cessna dimensions behind wing strut. Now with full tanks I can see fuel siphoning out the vent in flight. Any ideas? Plane has monarch caps and just the one vent tube on lh wing

That little tube is to let air in not let fuel out. There is a check valve in thee that may be the problem. I have had two 182B's and now have a 56 182. When your tanks are completely topped off the vent in the overhead that connects the two tanks fills with fuel and that can sometimes mess things up. I always take off on both tanks then switch to left tank only for the first hour. That helps.

Tim

McFarlane sells a replacement vent tube, modified to have a high point which should eliminate or at least reduce leakage, it might fix your problem.

http://www.mcfarlaneaviation.com/Produc ... C0716122K&

That is the vent tube i installed. I am thinking i don't have the vent hinge at the top. I was more worried about positioning the vent so it wouldn't rub the top of the bladder. Wouldn't it have been smarter to label the vent with "up" instead of "hinge"?

The fuel vent check valve in the left bladder has a small (#60) hole in it, and the tubing it is attached to should also have a #60 hole drilled in it (according to a diagram I found of the assembly in Tech Note No. 037 from the Cessna Pilots Association). These allow expanding fuel vapor and air to escape the bladders, but also allow fuel from a brimming-full bladder to pool in the vent tube. I find that when I have completely full fuel and hit some chop the fuel in the vent tube can get thrown above the high point that is intended to keep the fuel from dribbling out on the ground (I also have the McFarlane modified vent tube). In my experience this is not a continuous siphon but rather a quick "poof" of fuel vaporizing out the vent tube after hitting a bump, so disregard this if you're seeing a continuous stream of fuel leaving your plane! I do as qmdv does and burn off my left tank for an hour before switching back to both.

I have never seen an overhead vent (as on the early 180's) dribbling or streaming fuel out.
Unfortunately AD 90-21-08 dictates that if the LH bladder comes out of the airplane, you must convert it to the incontinent underwing vent-- a big move backwards IMHO. Grrr.