Cherokee fuel sump blocked?

jmarine225

jmarine225

Pre-takeoff checklist
Joined
Jan 19, 2020
Messages
241
Display Name
Display name:
Jmarine225
I have a Cherokee and recently had the two wing fuel sumps replaced as they had been leaking. Now the one under the right wing appears to be blocked with some kind of funk so fuel only trickles out. I can sometimes wipe a tiny tiny bit of dark slimy substance from the tip of the fuel tester I plan on replacing the whole sump as the a&p but a used older one in there but it had a new o-ring. Any other thoughts?
 
Mud dauber or other nefarious insect may have decided that's a nice place for a home. Happens on occasion. Try cleaning it out with a stiff wire and a blast of compressed air. If that doesn't work, time to remove the whole assembly and see if the obstruction is in the tank or the sump valve itself is bad.
 
You may have some foreign material from the tank that's partially blocking the flow.
Or it's possible the mechanic used a bit too much thread sealant installing the sump drain and a bit of that has got into it.
 
I beleive that @steingar suggests you just seal it off and forego sumping in the future.
 
JOhnH said:
I beleive that @steingar suggests you just seal it off and forego sumping in the future.
Click to expand...

On most airplanes the fuel tank sump drains are threaded in, and usually straight forward to replace. Some old-timers will repair them with new O-rings, but I prefer to replace the whole assembly. As @Capt. Geoffrey Thorpe noted, they aren't very expensive.

If I recall correctly, @steingar owns a Mooney?
A friend of mine bought a 1966 M20E last year. During the pre-purchase inspection it was discovered both tank drains had been deliberately plugged off sometime in the past. Turns out on these older Mooneys the sump valves are not threaded in to the fuel tank and can't be changed if they start leaking. He queried the seller who told him "he never sumped the fuel tanks".
I think my friend said the approved fix his mechanic did was to leave the old ones plugged and install a new sump drain fitting near the original location, which cost an AMU or two.
 
Last edited:
I think I would drain tank, remove sump, flush tank and replace drain
 
GRG55 said:
On most airplanes the fuel tank sump drains are threaded in, and usually straight forward to replace. Some old-timers will repair them with new O-rings, but I prefer to replace the whole assembly. As @Capt. Geoffrey Thorpe noted, they aren't very expensive.

If I recall correctly, @steingar owns a Mooney?
A friend of mine bought a 1966 M20E last year. During the pre-purchase inspection it was discovered both tank drains had been deliberately plugged off sometime in the past. Turns out on these older Mooneys the sump valves are not threaded in to the fuel tank and can't be changed. He queried the seller who told him "he never sumped the fuel tanks".
I think my friend said the approved fix his mechanic did was to leave the old ones plugged and install a new sump drain fitting near the original location, which cost an AMU or two.
Click to expand...
There is a Mooney SB detailing how to replace the original, riveted in drain valves. I did one of my wings last annual due to a slow leak from the drain.
 
GRG55 said:
On most airplanes the fuel tank sump drains are threaded in, and usually straight forward to replace. Some old-timers will repair them with new O-rings, but I prefer to replace the whole assembly. As @Capt. Geoffrey Thorpe noted, they aren't very expensive.

If I recall correctly, @steingar owns a Mooney?
A friend of mine bought a 1966 M20E last year. During the pre-purchase inspection it was discovered both tank drains had been deliberately plugged off sometime in the past. Turns out on these older Mooneys the sump valves are not threaded in to the fuel tank and can't be changed. He queried the seller who told him "he never sumped the fuel tanks".
I think my friend said the approved fix his mechanic did was to leave the old ones plugged and install a new sump drain fitting near the original location, which cost an AMU or two.
Click to expand...
Mooneys have wet wings, and now that they're 40 and 50 years old they leak. A lot of folks will have them "sealed" by their local A&P. I bet some ham-handed A&P sealed your friend's tanks, wasn't careful and went right over the sumps. The nice thing is Mooney sumps don't leak, though the nose sump is, well, a tad idiosyncratic.
 
steingar said:
... I bet some ham-handed A&P sealed your friend's tanks, wasn't careful and went right over the sumps. The nice thing is Mooney sumps don't leak, though the nose sump is, well, a tad idiosyncratic.
Click to expand...

I thought the conventional fix for the tank leak problem on a Mooney was to install a bladder? I imagine there's a small loss of fuel capacity with that method however?
 
steingar said:
Mooneys have wet wings, and now that they're 40 and 50 years old they leak. A lot of folks will have them "sealed" by their local A&P. I bet some ham-handed A&P sealed your friend's tanks, wasn't careful and went right over the sumps. The nice thing is Mooney sumps don't leak, though the nose sump is, well, a tad idiosyncratic.
Click to expand...
This is just plain wrong. Mooney sumps are no different than any other sump. I replaced one of mine recently because it was leaking. Please stop repeating this kind of incorrect crap.
 
GRG55 said:
I thought the conventional fix for the tank leak problem on a Mooney was to install a bladder? I imagine there's a small loss of fuel capacity with that method however?
Click to expand...
That is one fix, but it’s not that difficult to reseal the wing. Some decide they don’t want to do it again so they put in bladders instead. There are pros and cons to each.
 
Back to the topic, I’d guess some sealant or other FOD is plugging the drain. I’D try replacing the drain.
 
If it's black slimy stuff, consider this a second vote for ham-handed overuse of thread sealant when the "new" sump valve was installed. Take it out (which will of course drain the tank), clean it up and make sure it's working properly, then put it back in with sparing use of sealant around the threads...or spend the $20 and put in a new valve and feel even better.
 
MuseChaser said:
If it's black slimy stuff, consider this a second vote for ham-handed overuse of thread sealant when the "new" sump valve was installed. Take it out (which will of course drain the tank), clean it up and make sure it's working properly, then put it back in with sparing use of sealant around the threads...or spend the $20 and put in a new valve and feel even better.
Click to expand...
Yep. That’s what it is. I had two of them replaced and it’s only in this one tank. I ordered a new one to replace it.
 
MuseChaser said:
(which will of course drain the tank)
Click to expand...
If you are quick with your thumb, you can replace the drain valve with a loss of no more than a couple cups of fuel - most of which will run down your arms, soak your shirt, and possibly splash in your face.

(Make sure that the new valve is less than an arms length away.)
 
Yeah I purchased a new one expecting delivery this week. I’m gonna try the air can and see if that clears it out. Just hoping some of that gunk doesn’t make its way to a fuel line.
 
Capt. Geoffrey Thorpe said:
If you are quick with your thumb, you can replace the drain valve with a loss of no more than a couple cups of fuel - most of which will run down your arms, soak your shirt, and possibly splash in your face.

(Make sure that the new valve is less than an arms length away.)
Click to expand...

:yeahthat:

This is how I do it without draining the tank.
Helps to have an assistant, but not mandatory.
Make sure you prep the new valve with a fuel resistant tread sealant. I use this:
ptx-9403.jpg

Spin out the old valve, let a bit of fuel flow out to clear any sediment that might be near the drain, plug it with your gloved thumb, grab the new valve and thread it in. Do not overtighten (most common mistake people make).
 
jason gula said:
Yeah I purchased a new one expecting delivery this week. I’m gonna try the air can and see if that clears it out. Just hoping some of that gunk doesn’t make its way to a fuel line.
Click to expand...
That is why I suggested flushing the tank out.
 
GRG55 said:
:yeahthat:
I use this:
ptx-9403.jpg
Click to expand...
That stuff hardens over time and makes removal difficult. I always used Fuel Lube, now known as EZ-Turn. It's handy for an awful lot of other stuff, too.
proxy-image

It's fuel-proof and doesn't harden. It was designed for lubricating plug-type fuel valves. The only thing I've ever found that will dissolve it is acetone.
 
As mentioned before, There has been a bug build a nest inside the drain cock. I've had that happen on numerous occaisions. Except the one that leaks. ;)
 
Capt. Geoffrey Thorpe said:
If you are quick with your thumb, you can replace the drain valve with a loss of no more than a couple cups of fuel...
Click to expand...
Actually, it's considerably less than that. More like a few tablespoons. Have the new valve and a solid plug ready. Keep the old valve close. (If you fumble the new valve, you still have two chances to plug the hole.

If you don't have a replacement valve or don't want to wait for it to arrive, use a solid plug from the hardware store, clean the existing valve, and replace.
 
You must log in or register to reply here.
Back
Top