Incontinence, of the Fuel Kind!

[WSHIII]

My new to me '52 model has an auxiliary fuel mod, with an 18 gallons tank in the floor of the baggage compartment.

There is a snorkel vent right on top and in the middle of the wing, right over the cockpit. Well, it pukes fuel, at least when "topped off", all over the fuselage/empennage.

From the previous owner, the drill is supposed to be. Run the right tank out. Then switch to the left and turn on the transfer pump to refill the right tank from the aux tank.

Could, someone give me a little primer of the tank schematic, with regards to which tank(s) are being vented with the snorkel vent? I suppose it's mainly the aux tank, as I have never seen one before on a stock Cessana. And, is there a rule of thumb to minimize this overboard discharging of fuel from the aux fuel tank, like keeping the aux tank below a certain level to reduce this "discharge".

FWIW, it appears I have the stock self-venting "red" Cessna fuel caps on the main tanks and a non-vented cap for the aux tank.

[n2582d]

Check out this link. The flight manual supplement you'll find on that link is required to be on board your plane. I believe your aux. tank cap should be vented. There should also be a one way check valve that prevents fuel from flowing back into the aux. tank. Do a search of "Javelin" for an evening of reading.

[WSHIII]

Gary,

Perfect!

Good stuff, thanks.

[blueldr]

The "gooseneck" vent on the top of the fuselage is teed in to the wing tank cross cabin vent line. This vent line is attached to the front top of each wing tank. When the wing tank is full, the cross cabin vent
line will flood with fuel if the nose of the airplane is lowered. The "gooseneck" is located in a low pressure area and liquid fuel can be sucked out in this condition.
If you're going to be shooting landings, try to do it when the fuel tanks are depleted enough to keep the subject vent line free of liquid fuel when the nose is lowered.
This problem, that occurs on all stock C-170 vent systems, can be alleviated by blocking off the "gooseneck" and installing a bootlegged vent system as is used on all the later Cessnas where the vent line terminates on the under side of the left wing just behind the wing strut attach point.
This relocation of the vent is part of the STC installing the Continental IO-360 IAW the XPMods STC.

[WSHIII]

Blueldr,

The "gooseneck" vent on the top of the fuselage is teed in to the wing tank cross cabin vent line. This vent line is attached to the front top of each wing tank. When the wing tank is full, the cross cabin vent
line will flood with fuel if the nose of the airplane is lowered. The "gooseneck" is located in a low pressure area and liquid fuel can be sucked out in this condition.
If you're going to be shooting landings, try to do it when the fuel tanks are depleted enough to keep the subject vent line free of liquid fuel when the nose is lowered.
This problem, that occurs on all stock C-170 vent systems, can be alleviated by blocking off the "gooseneck" and installing a bootlegged vent system as is used on all the later Cessnas where the vent line terminates on the under side of the left wing just behind the wing strut attach point.
This relocation of the vent is part of the STC installing the Continental IO-360 IAW the XPMods STC.

Very informative!

Thank you.

[blueldr]

You're most welcome.
Unfortunately, the tee at the bottom of the gooseneck vent is hidden behind the cabin ceiling headliner,and thus is almost permanently missed on routine inspections including annuals. This can result in non detection of deteriorated coupling hoses on the bottom of the vent tee. Dereriorated hoses can and will leak fuel when the cross cabin vent line floods with full tanks and a nose low attitude.
Believe me when I tell you that a gasoline saturated headliner, discovered at an altitude of nine thousand
feet over very serious mountain terrain, will draw your pucker string up so tight that it will take a week to loosen.
As the old Packard Automobile ads used to say, "Ask The Man Who Owns One!".

P.S. In the event of an elusive fuel smell source, be sure to check these vent line tee coupling hoses.

[edbooth]

The "gooseneck" vent on the top of the fuselage is teed in to the wing tank cross cabin vent line. This vent line is attached to the front top of each wing tank. When the wing tank is full, the cross cabin vent
line will flood with fuel if the nose of the airplane is lowered. The "gooseneck" is located in a low pressure area and liquid fuel can be sucked out in this condition.
If you're going to be shooting landings, try to do it when the fuel tanks are depleted enough to keep the subject vent line free of liquid fuel when the nose is lowered.
This problem, that occurs on all stock C-170 vent systems, can be alleviated by blocking off the "gooseneck" and installing a bootlegged vent system as is used on all the later Cessnas where the vent line terminates on the under side of the left wing just behind the wing strut attach point.
This relocation of the vent is part of the STC installing the Continental IO-360 IAW the XPMods STC.

There was also a "kit" available some years ago that included a sleeve that slid over the gooseneck outlet, a light weight composite ball and a cotterpin. The goosneck was drilled for the cotterpin, the ball slid into the gooseneck and the sleeve slipped over the outlet.The sleeve had a smaller outlet and formed the seat for the ball acting as a checkvalve. This kept most of the fuel which would flow out of the vent under certain conditons contained. I think this flow out the gooseneck problem was probably increased when the required vented fuel cap was installed way back when.....

[blueldr]

I believe that there were previously numerous reports that this ball check modification was not too successful.

[edbooth]

I believe that there were previously numerous reports that this ball check modification was not too successful.

I have had one on there for years. You are correct, it is not 100%, but better than it was without....
Just keep it straight and level and fly in smooth air with full tanks....

[blueldr]

If you're only going to fly straight and level in smooth air with full tanks, you don't need any modification of the vent system.

[GAHorn]

The check ball system was removed years ago by Cessna service bulletin, Ed.
It introduced a whole new set of problems of its own.
You are flying without Cessnas blessing if you haven't accomplished the new service bulletin issued twenty years ago.

[WSHIII]

Another question regarding the Javelin mod. I haven't come across it yet but, can you transfer fuel while on the ground, i.e. taxing around, waiting on the engine to warm up? Or only straight and LEVEL?

[blueldr]

I would think that aux fuel could transferred any time the transfer pump inlet is submerged in fuel. Of course, there needs to be space in the tank you're transferring fuel to.

[WSHIII]

I would think that aux fuel could transferred any time the transfer pump inlet is submerged in fuel. Of course, there needs to be space in the tank you're transferring fuel to.

Yeah, I agree. I guess I was more curious about any specific "prohibition" in the manual against it. I've since found something in the instructions where they say to transfer the fuel "in level" flight but I can't find any prohibition against ground transfer.

Do you happen to know where the aux tank "pick up" is? I haven't had the cover off the tank yet and can't find anything definitive showing its location.

And thanks for the headsup on overhead "teed" connection for the Gooseneck vent. A fuel soaked headliner doesn't sound like much fun at all, especially over hostile terrain.

[WSHIII]

Hey Dick

I had my suspicions that may have been you. All the pieces of the puzzle were starting to fall in place, then I found an older thread that confirmed it. Skip Harwood here, ship pilot from Virginia. I'll shoot you a PM later and catch up with you and fill you in on the "new" airplane, among other things.

Missed you at Johnson Creek Labor Day weekend on my way back east! The weather/heat finally broke, very pleasant week, and had fun with Phil and Roxxy!

Hope everything is going well with you,

Skip