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  #11  
Old 12-06-2015, 08:28 AM
Kellym Kellym is offline
 
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Quote:
Originally Posted by paul330 View Post
Leak is definitely in the tunnel, not the roots. No drain plug on the gascolator.

Guess my job tomorrow is to start disconnecting pipes and inspecting - but how can a leak be intermittent? I pressurize to 25psi with the electric pump and nada.....
You can only pressurize with the boost pump from the pump to the firewall. If no leaks there, your leak is in the unpressurized portion from the tank to the boost pump. If you have a means of applying pressure to the fuel vent tube with a NON-electric pump up to no more than 1/2 psi (to not damage your tanks) you might then be able to see where the leak is.
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  #12  
Old 12-06-2015, 12:03 PM
N15JB N15JB is offline
 
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Would UV dye be helpful in locating this leak? I found it to be very useful in locating a very small leak on my accessory case. Once I found the right combination of dye and UV light, it was obvious where the leak was.
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  #13  
Old 12-06-2015, 04:18 PM
sblack sblack is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post

After the above two suspects, I'd guess you have a fuel line fitting problem. Assuming you already looked for a loose fitting, tightening of already tight fittings will not help. Under no circumstances should you attempt to "seal" the leak with RTV or other such stuff.

Carl
I use SealLube on all npt fittings, carefully appied to ensure that there is none on the first couple of threads. It has helped me fix very pesky tiny weeping of fuel. Numerous pros have told me this is an acceptable practise. Certainly not rtv!
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  #14  
Old 12-06-2015, 11:10 PM
paul330 paul330 is offline
 
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Thanks everyone for the tips. Seriously, I was joking when I said "let it go" - I was fully aware of the lost RV to the tunnel fire

Anyway.......

I have pressurized the system to the firewall. I have slightly pressurized the tanks. I can find absolutely no evidence of a leak anywhere So, I am beginning to think I am chasing ghosts. There were relatively large stains around the gear legs and belly and only minor ones in the cross bay and tunnel. I am beginning to think that there was some sort of spillage at the roots which migrated inwards rather than the other way round.

On my last flight, I went through a mountain pass and we had a couple of pretty large jolts in turbulence. I'm feeling that there was probably fuel that came out of the vents - I had about a 3/4 fuel load at the time. Now, if the vents are leaking, then it needs fixing but it's not nearly as serious or dangerous as a tunnel leak. Even with full tanks, though, there is no sign of a vent leak. I am therefore thinking this was a one-off spill caused by a couple of negative-G bumps.

I'm going to clean off the stains, button everything up and try a local flight to see if there is any recurrence.

Thanks again for the help. I'll let you guys know how it goes. Due weather and Christmas shopping, Wednesday looks favourite......
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  #15  
Old 12-06-2015, 11:20 PM
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9GT 9GT is offline
 
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I wrap all my fuel joints in the tunnel and the wing roots with a small piece of white paper toweling held in place by a piece of tape. I inspect these whenever I have access and replace. If a single drop of dyed fuel finds its way past a joint, I will know where it came from.
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  #16  
Old 12-08-2015, 09:55 AM
paul330 paul330 is offline
 
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Quote:
Originally Posted by 9GT View Post
I wrap all my fuel joints in the tunnel and the wing roots with a small piece of white paper toweling held in place by a piece of tape. I inspect these whenever I have access and replace. If a single drop of dyed fuel finds its way past a joint, I will know where it came from.
Good tip - I'll do it next time I have the tunnel panels off. However.......

Just done a 50 minute flight. Steep turns, stalls, half a dozen circuits. Not a sign of any fuel leak anywhere. Go figure......
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  #17  
Old 12-09-2015, 11:55 PM
paul330 paul330 is offline
 
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OK, two flights (one 1/3 tanks, one full) - nothing. Third flight, fuel stains around the roots and legs and smell of fuel.

The last flight, I again had some moderate turbulence. Could fuel leaking through the filler caps migrate to the roots and get in that way?
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  #18  
Old 12-10-2015, 02:10 AM
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Dbro172 Dbro172 is offline
 
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Fuel leaking through the filler caps will be going straight back in flight, doubt it would even make it to the wing root when parked.

You haven't by chance filled the tanks tight full in cold temps and move to warm hangar? The fuel will expand and leaks may become apparent.

It it possible you have a leak on the rear baffle or the root rib of the fuel tank... Both leaks could travel in front of the main spar to the root and into the floor of the cockpit.

You might have to pull the tank, you might actually try (with precaution) using fuel then in the tank to detect the leak.

Have you disconnected and physically look at the flare of each fitting? Over tightening a flared fitting will cut (smash) the flare right off inside the nut and it will leak
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  #19  
Old 12-10-2015, 07:21 AM
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aturner aturner is offline
 
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If the stains appear only when tanks are full, then you almost certainly have a leaking vent. It could be the bulkhead fitting isn't sealed up, or the flare fitting is defective. Wrap you tissue around the fitting where the vent exits the tank, and see what you have.
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  #20  
Old 12-10-2015, 10:19 AM
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Auburntsts Auburntsts is offline
 
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Have you looked at your fuel level senders? I had a leak from my left tank -- after one flight I had a strong fuel smell in the cabin. A quick inspection showed blue stains on the left bottom wing root fairing. Took of the top fairing and there were blue stains forward and aft of the spar in the wing root area but nothing outboard indicating a baffle leak nor inboard under the pilots seat. There was also nothing discernible from any of the fittings or line in the root area. Ended up wiping each part with a paper towel and bingo it was weeping from the sender. Took it off, applied some fuel appropriate permatex gasket maker to the sender and that fixed the problem.
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Last edited by Auburntsts : 12-10-2015 at 10:34 AM.
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