How high do you fill the tanks?

[Zebedee]

My instructor told me to fill AUX tanks as much as possible with the fuel level sitting just below the lip. This leads to gas "leaking" out and dripping off the back of the engine behind the wing. Not out of any vents or drains, just off the fairing on the back of the engine.

I had right AUX tank fixed and mechanic said the neck on the tank was not sufficiently caulked/glued. Now the left engine is doing it.

I think I am filling the AUX tanks too much and should maybe leave the level down from the lip. What do you guys do?

MAIN TANKS

I usually fill main tanks all the way to the top, as slowly as I can. This helps prevent venting due to filling too quickly. However, any movement of the plane as I climb in and out leads to venting, usually from the right wing.

I also think all this venting contributes to the Jet fuel smell that seems to invade the cabin, more so when the tanks are full and the AC is on. I'm going to have mechanic check for some of the fuel leaks discussed on this forum at the next annual.

How high do you fill the main tanks and have you noticed any issues when filling it all the way to the top.

Thank you in advance

[bdbogle]

Typically, Aux tanks as you described. Maybe a bit lower in the neck as long as they are roughly even. Main tanks, typically to the button of the cap safety wire tab. Any higher and it'll start venting like you mentioned.

[mfdutra]

I fill the aux tanks to the bottom of the neck. I instruct the guys to touch the neck and stop. More than that, it leaks.

[Chris]

I have frequently filled the AUX tanks on the 42 to the very top without any trouble. I'm surprised that you can't do the same on the 62. I never fill the mains all the way to the top, though. It's not worth the trouble and mess, and the local FBO has started charging cleanup fees if your tanks vent JetA onto their ramp.

[Bryce]

I've always filled the auxiliary tanks up to just below the top, and have never had any leaking. Maybe I shouldn't fill them so high. Mains seem to always vent. I tell the line people they need to fill the tanks really slow or they will vent and if they're not careful they will overflow. I say I don't care about venting, but overflow and we'll have a problem. One time the FBO made a comment about it leaking, I said I warned the line guy it would do that if he filled the tank fast. End of discussion!

[Boatguy]

I filled the aux tanks to the bottom of the neck. No leaks, lots of range.

[Zebedee]

Can you see the "neck" on the aux tank?

I have added 12 gallons in each aux tank, plus whatever I couldn't get out with aux pumps. Guages showed 17 gallons in each aux tank, seemed high. But no leaks.

I like filling tanks so I know what I have. Filling to neck or tab for safety chain in main tanks, leaves me short on 86 gallons.

I wonder how much fuel is in the tanks with either of these measures.


Thanks for all the advice.

[Soareyes]

DA42:
Aux tanks can be filled to the top of the filler neck, right to the cap, they never leak.
Main tanks: Left side, can fill to the bottom of the rim, no leak. Right side, there's the problem. Got to keep it a finger's width below the bottom of the rim or it overflows out the fuel vent onto the ramp. I always warn the fueler but they usually put in too much anyway.

[Zebedee]

I had my right aux tank neck fixed for leaking when I filled the tank to the cap. The left is now doing the same thing and I am sure the same person screwed up both tanks.

I think I will fill Aux tanks to what I think is 17 gallons, 15 plus whatever I couldn't scavenge from last flight.

I will fill mains to t
he tab the security chain for file cap is attached to.

I will get Left Aux tank fixed as annual.

Thanks for the advice.

[jc7204]

I instruct to “fill but leave an inch at the top” and while a tad subjective, it seems to work.