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Fuel indicator tube changed color

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One of my fuel indicator tubes got a bit foggy. I got them replaced in the summer. The other one is fine. Any idea what causes it? Thanks!

4E645CD7-8166-4EE3-AF84-68EA9927FAB2.jpeg

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10 hours ago, Tom Baker said:

Normally something in the fuel. It is odd that one side would get cloudy, and the other side stayed clear. 

Is it really necessary to pull the wing to change it, or can it be done in place ? Looks tight.

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6 hours ago, Roger said:

Is it really necessary to pull the wing to change it, or can it be done in place ? Looks tight.

It can be changed without pulling the wings, but the easiest and quickest way is to pull the wings. The wings need to come off for the inspection and rubber replacements anyway, so it is a good time to replace the sight tubes.

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Is there any way to modify the sight tube such that one no longer has to pull the wings?  Different design or fitting?  I've never like that sight tube, anyway, so maybe I'm just whining.

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2 hours ago, Jim Meade said:

Is there any way to modify the sight tube such that one no longer has to pull the wings?  Different design or fitting?  I've never like that sight tube, anyway, so maybe I'm just whining.

On an ELSA I'm sure you could come up with something, maybe a tempered glass (or fuel-resistant hard plastic) tube with different end fittings.  It might be a major undertaking, and I'm not sure it's worth it since you should pull the wings biennially for inspection anyway.  Once the wing is out the sight tube replacement is pretty trivial.

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Dakota Cub has nice fuel tubes that can be cleaned without removal, I used them when converting my J3 cub to a super cub.

The problem is installing them at the exact height in the CT,  also you have to remove the wings every two years. I looked at this before but it's not really worth the effort at least in my opinion. I use clear Tygon 210 that I buy in bulk.

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Wing inspection isn’t just 2 years.

The checklist says 2 years or the first 100 hrs. after that. So some can easily make 3 years.

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9 hours ago, Roger Lee said:

Wing inspection isn’t just 2 years.

The checklist says 2 years or the first 100 hrs. after that. So some can easily make 3 years.

You are correct the the tube itself can make it more than two years, but I can't remember a single instance where the fuel level was easily visible after two years of running auto fuel. If they are running 100LL or Swift, then no problem. As both a mechanic and pilot not being able to easily see the fuel level is an issue that needs corrected.

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Use of clear poly tubing like FD originally used. Mine all seem to last the 3 years. Use of that yellow Tygon tubing is terrible right up front.

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Tom,

Is that the yellow Tygon tubing? Tygon also Mfg's clear tubing.

When I did a research project just before my first hose change I called 5 tubing Mfg's. They all said that tubing was all pourus up to a point so that's why all tubing absorbs that brown stain within the auto fuel. The 100LL doesn't have a dark enough color to make it bad. I have pulled the standard clear poly tubing off planes that had it for 5 years. Even though it fells hard you can still bend it in half without it breaking.

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The tubing Flight Design sells is clear. At one time Lockwood was selling the yellow tubing. I had one recently that you couldn't see the fuel level, and it was hard as a rock. It was my first time working on the airplane, and I have no idea when it was changed last if ever. The fuel hose in the wingroot had never been replaced. As for staining, I wouldn't really call it stained. In my experience it is more of a film that develops on the inside of the tubing, or at least a combination of the two.

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On 2/4/2021 at 9:19 AM, Tom Baker said:

You are correct the the tube itself can make it more than two years, but I can't remember a single instance where the fuel level was easily visible after two years of running auto fuel. If they are running 100LL or Swift, then no problem. As both a mechanic and pilot not being able to easily see the fuel level is an issue that needs corrected.

I went three years before my first wing removal and I could still read the sight tubes.  They were pretty dark brown, but readable.  Interestingly, I find the Tygon tubes turn brown, and the Home Depot vinyl tubes Roger recommends turn a greenish yellow (using 93 octane mogas).

I will say the vinyl tubes seem to mold themselves tighter to the fittings over time, and can be a real bear to get off the barbed nipples.

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On 2/5/2021 at 11:10 PM, Tom Baker said:

Oh, I also had one airplane that the tube was rotten. It completely fell apart when I tried removing it.

That's scary. 

I have thought about a split tube in flight...I guess I'd stuff a rag in the sight tube witness hole to force the fuel to weep out along the fuselage instead of into the cockpit until I could get on the ground.

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What size are the tubes and recommended place/brand to buy from ?   I didnt keep track where i bought mine 4 years ago but its still  clear as day 1 (rock hard though)

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10 hours ago, cdarza said:

What size are the tubes and recommended place/brand to buy from ?   I didnt keep track where i bought mine 4 years ago but its still  clear as day 1 (rock hard though)

I sent you an email with your questions answered.

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