Fuel Tank 337G

[edasmus]

Hey Mark,

Thanks for the info. I will investigate. I had a long talk with your IA last Thursday about your tank situation. He gave me all the details. I am quite aware of the complexity of our fuel system and over the years have considered complete removal, inspection, and repair. My shop (and yes you do know the one) has warned me about the enormity of that job and has convinced me to leave alone unless I see signs of trouble. This leak I have been chasing for a few months now. My right wing was showing trouble a few years back and replacing the cork sender gasket on that side cured that problem. When I started seeing trouble on the left side, the same cork gasket is where we started. We did see obvious signs of leakage there. About three months ago we replaced it but unfortunately that did not solve the problem this time. When we opened up that inboard panel a few weeks ago during the annual, that area was perfectly clean so we knew the leak was coming from somewhere else. The shop traced it to a fitting on the inboard tank between the boom and the wing root. They could clearly see blue staining all over the fitting and all over the bottom of the inside of the wing draining down to the wing root, which is where I was seeing it. The problem really got ugly after four attempts at re-installing the tank after the attempted repair and still leaking. Now they claim it appears to be leaking through a weld joint and they fear they cracked the tank while removing the old fitting. At least that is the story. I will know more in the morning. I actually have not spoken with the shop since the middle of last week. I have just been getting cursory emails from the IA with the bad news.

Stay tuned.

Ed

[hharney]

Ed / Mark

The D model tanks do not have the large interconnect between the mid-main and the inboard aux. The D model has the older style main tank and independent auxiliary tanks. The G model like yours has all tanks interconnected and the D is separate mains and aux's. The D model also has a service port.

The G model is the blue figure attached and the D model is the white figure attached. That should explain the difference. Not sure I understand why the fitting cannot be repaired. I have had to repair a fitting like that on my main tank (inboard, mid) and it was welded with no issues. Sorry to hear the problems.

[Gord Tessier]

I had a fuel leak in my 73 G model. It turned out to be nothing more then the gasket in the fuel cap. With the tanks full, I could see with a bright light the fuel migrating or weeping out around the filler cap and then down the wing root. Cheap fix.

[hharney]

Gord

Very common area for Cessna. Sounds like based on the diagnosis that Ed gave above he has already been there done that. The gaskets on the fuel senders are troublesome critters and if you ever install a new fuel sender or gasket remember do not remove the wires at the terminal screw that has the putty on it. You have to take the wires apart at the butt connection or the unit is void for warranty if needed. Learn the hard way.

[SkyMac]

Hi Herb

Any learnings on fitting the new gaskets, I will be replacing all mine before I close the wings. I have all the new gaskets and those little rubber washers ready to go. Mind you it will be a couple of months before I get to it.


I found two sender units leakering when I pulled the tank covers off, also I have read a few comments on leaking fuel tanks over the last couple of days. Of my 6 tanks and the two little sub tanks I will carry out in total 7 welds on very small splits / pin holes. Each repair is welded then it has another circular disc welded over that, according to the approved engineer who is conducting the repairs, this is a very common issue and he does them all to often.

Anyway I am aiming for a leak free fuel storage and supply

Regards
Dave

[Mark Hislop]

Hi Ed.

If they were able to get the inboard tank in and out without removing the outer tanks, they are a lot smarter than I am. (Not a very high bar, I'm afraid.) I couldn't figure out a way to get new hoses on without removing all of the tanks and putting them in in sequence. For actual professionals with the right tools, I don't think it would be too tough. For an amatuer like me, well...... If you want to see what the outboard tank bay looks like, feel free to stop by my hangar any time. I'm there most evenings. I'm finishing up the left wing, and then starting the right wing.

[Mark Hislop]

Thanks Herb. I didn't know that. Hopefully, Ed can find someone who is parting out a later model with the same tanks. Or get somebody to repair his tank.