182 bladders and fuel senders

1

182driver

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182driver
I finally got my 1976 Cessna 182P and managed to get checked out in it before the engine (well past TBO) flunked its oil change big time. I ended up getting a brand new Continental O-470 from Air Power Inc; they were great to deal with and cheaper than factory direct.
I also got a JPI EDM-900 engine monitor that includes fuel gauges. JPI technical support is responsive, but that is anther story. Let's just say my fuel gauge readings are pretty random and it is probably my senders.

And, maybe I need new bladders. In the 2 wintery months that I had the plane, I usually had gas dripping out of the left wing root down the side of the cabin. I had been filling the tanks quite full - my mechanic says I was overfilling them. When calibrating the EDM-900, I put a measured 38 gallons in each tank (full is 37.5) and the level is still well below where I used to fill to.

My mechanic says just replace the fuel senders and replace the bladers when they leak. I wonder if they already do. Even before I saw the plane, I had budgeted new bladders (aka fuel cells) since they were last replaced in 1999. I'm also a believer in preventative maintenance and fuel leaks sound dangerous and an expensive way to maybe ruin the interior with fuel stains, but then I would not replace the bladders every year. Every 15 years? Especially since the fuel senders need done anyhow?

Is overfilling the tanks even a potential issue? It seems to me that if I put in too much gas, it will come out of the fuel cap or the vent. I cannot think of any reason why fuel would end up inside the wing except for a leak, probably near the top of the bladder.

And yes Duncan, I know that you love your wet wings and I don't blame you.
 
Mine leak in the winter but not in the summer. I think the culprit is the gasket at the sender. Topping the tanks to the max definitely makes it worse on mine.
 
We had some small leaks that were chased to the little tubes that connect the top of tank vents and other tubing that was old and cracking in the wing root.

We had those replaced and no small leaks since.

The left bladder let go in the hangar a while after that. But it was unrelated.

If your mechanic can't find the leak, find another mechanic. Seriously.

Some (rightly) have an aversion to messing with it. Bladders are a PITA to change as are the hoses.

But if it's leaking, find it and fix it. If it's coming out of the wing root, it can be found.
 
denverpilot said:
But if it's leaking, find it and fix it. If it's coming out of the wing root, it can be found.
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Some fuel leaks can only be found with the bag removed. If in doubt, would you reinstall? It requires a set of plugs, blank off plates and a method to pressurize, then a soap & water bubble check.
Then a method to patch. These aren't a bike inner tube. they require special cleaners and glues.
My best advice replace it.
 
Find the leak, fix the leak. There is no option.

A digital instrument is very accurate and any float arm transmitter is susceptible to bobbing around on the surface of the fuel. The combination makes for quantity readouts that go up and down constantly. My own new transmitters are McFarlane and when calibrating the instrument each and every gallon registered through 39 gallons a side. The float position change and the subsequent resistance change between each gallon was very small. If you've calibrated a digital fuel instrument you know how still the plane has to be. That doesn't happen in flight. The result is fluctuating quantity readouts and the lower the tanks the worse it gets. I never wanted or needed a fuel totalizer until after I installed a digital fuel qty instrument.
 
I've always heard that bladders will go bad if they are EMPTY too much, don't think topping them off would cause an issue.

If you're replacing fuel senders look into the magnetic ones and the EI primary instrument replacements, might as well upgrade to better tech while you're in there, also you should do the install mostly yourself, I hear it's more elbow grease than skill.


How did your engine fail its oil change?
 
Tom-D said:
Some fuel leaks can only be found with the bag removed. If in doubt, would you reinstall? It requires a set of plugs, blank off plates and a method to pressurize, then a soap & water bubble check.

Then a method to patch. These aren't a bike inner tube. they require special cleaners and glues.

My best advice replace it.
Click to expand...


Well if the mechanic hasn't looked at the connections and just says he thinks that's where it's coming from, my point was the owner had better make him look.

After that if you still can't find it, there's no economy in repairing the tank. Replace and be happy.

But if he hasn't looked... And is only guessing... Make him look. Or better, find someone interested enough in your safety and the condition of the aircraft who wants to look.

None of the above is necessarily cheap, of course. Welcome to owning something built in the 70s that wasn't even as well built as a 70s car. Heh heh.

It also might be worthwhile to take a trip down memory lane and see just how old the bladders are. Opinions vary, but there's a magic age where you might as well just yank them.

Also helps to know if you're lucky enough to still have one that's under warranty. Unlikely, but it happens. Most manufacturers at least pro-rate the price of new if yours failed before the warranty day. Clock is ticking.

If you replace one or both, put better fuel drains in. The Eagle STC'd ones are nice.
 
SteveCanyon said:
Mine leak in the winter but not in the summer. I think the culprit is the gasket at the sender. Topping the tanks to the max definitely makes it worse on mine.
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You hit the nail on the head. I believe it is the gaskets themselves shrinking from the cold. The solution is to tighten the screws around the sender ports regularly. Replace the gaskets when you replace the bladders. It is best to keep the tanks full - especially if the plane is tied down outside. My former mechanic had a '50s 180 that was always hangared - and said it had the original bladders.

By the way - tighten the screws around the fuel fillers regularly as well (say every 6 months). After finding some water in the tanks I noted that said screws needed tightening. Never one drop of water after that.

Dave
C-182 owner 36+ years
 
I haven’t asked my mechanic to look for the leak, if I have one. I’m sure he could find it, but I’m wondering about the magic age that was mentioned above. My bladders were last replaced in 1999. Are 16 year old bladders so old that I should just replace them rather than look for a leak? Certainly if they have to be removed to find a leak, then they are going to be replaced.

If I only have fuel finding its way into the wing when I put 3 more gallons in the tank than it is supposed to hold, do I really have a problem or should I just not do that?

I’m going to replace the senders, so should I just do that first and maybe the leak is at the sender gasket?

Does anybody know where to get the magnetic senders? Scott Philiben at CIES corp told me they hope to have senders for a 182 soon but he needs to get some original ones first to check the mechanical dimensions. The Cessna drawings are that unreliable.It doesn’t seem that CIES will have FAA approved senders in time to help me. Is there another supplier or another good option?

I bought the plane in November and was happy to get my checkout and training in it on the old engine. The old engine was a factory remanufactured one that was installed in 2002 and had 1650 hours on a 1500 hour TBO. When we did the oil change, we found a lot of copper in the filter, including some pretty big flakes. I had planned on getting the engine overhauled when I bought the plane, but the cost of factory new from Air Power was not much more than the overhaul, especially compared to the total cost. I’ve got just about everything new firewall forward at this point, including brand new powder coated baffles. Maybe I could have flown on the old engine a bit longer, but what was the point in delaying the overhaul by a few months? I had one cylinder fail in my 1985 180 HP Skyhawk in IMC with my wife and kids aboard, and I’m going to do what I can to not be there again. I had a bent pushrod and forced landing in my Dad’s 172 in nice VFR and within gliding distance of an airport with four on board, and that was bad enough. Dad dead-sticked that same 172 into Raleigh after one of those infamous ECI cylinders blew its top. New doesn’t always mean better, but I’m more conservative and less willing to take a chance on an engine being good enough than I once was.
 
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You have a good instrument. Use the senders that the instrument manufacturer advises you to use.
 
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182driver said:
I’m going to replace the senders, so should I just do that first and maybe the leak is at the sender gasket?

Does anybody know where to get the magnetic senders? Scott Philiben at CIES corp told me they hope to have senders for a 182 soon but he needs to get some original ones first to check the mechanical dimensions. The Cessna drawings are that unreliable.It doesn’t seem that CIES will have FAA approved senders in time to help me. Is there another supplier or another good option?
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There is more to it than just wapping the senders to CIES. BTW. I would have needed to add another wire to each fuel sender meaning run one for each sender from the instrument panel, through the fuselage through the wing and to the sender to make it work.

I doubt they will work with the old gauges either.


If you indications are flakey, I'd do:

#1 Verify all the wiring is corrosion free.
#2 All connections are tight
#3 Get new / or repaired senders (if they haven't been replaced in the last 20 years they are probably due)

Resistance float type Cessna senders should work with JPI. Also read the calibration procedure for it so you get an idea of how accurate it will be.


I installed a similar product using two repaired Cessna senders. The digital gauge is calibrated in 2 gallon increments with the airplane jacked and leveled longitudinally and laterally. The owner has been very pleased with the results. I'm a little jealous of it but I have a fuel flow and he doesn't.
 
denverpilot said:
Well if the mechanic hasn't looked at the connections and just says he thinks that's where it's coming from, my point was the owner had better make him look. .
Click to expand...

When you must make your A&P do any thing you best get another A&P.

but,, the only thing you can see are the connections in the wing butt. any other leak will require pulling the bag.
 
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bnt83 said:
I installed a similar product using two repaired Cessna senders. The digital gauge is calibrated in 2 gallon increments with the airplane jacked and leveled longitudinally and laterally. The owner has been very pleased with the results.
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There is an upgrade to capacitive system.
 
The wiring is all brand new and came with the EDM-900. JPI does not recommend a sender but their tech support suggested CIES. CIES has senders for a Cardinal but not for my Skylane (yet). The EDM-900 will work with just about sender, so that is not the limiting factor. I calibrated the fuel gauges myself with supervision from my mechanic - I'm a controls engineer, so this kind of stuff is easy.

My mechanic already tightened the senders to the tanks (and also the wires) so the next thing I am going to do is put about 40 gallons in each 37.5 gallon tank and see if they leak. Maybe my leak problem is already fixed. I'll get new senders as soon as I can find good ones. If I can't find good ones, I'll just get the same old-tech replacements.
 
I've never seen a Cessna fuel level sender but if it is an open wire wound variable resstor, the following should apply. I had fuel senders that provided erratic operation over the level range, frequently indicating zero. Cleaning the wire surface where the wiper arm rides using a pencil eraser made a vast improvement.
 
Interesting -
This is what I know - It appears that old analog senders and old analog gauges were meant for one another. If you modernize one - the other will drive you nuts.
I have several examples on the bench - it is an interesting observation. Digital Digital - Good Analog - Analog - OK

CiES builds senders for every aircraft - so the Cessna 182 (Bladder and Integral ) are in their wheelhouse. At this point they are the largest supplier to OEM Aircraft. They are powered so they do need a separate power and ground.

Capacitive is not your answer - Capacitive senders rely on a lot of interesting factors - Fuel type (as in hydrocarbon makeup), Fuel Temp, and Fuel density. They also rely on two conductive plates. With constant use and the washing effect of thrice daily doses of Jet A - they perform quite well. Left to sit in the moist fuel tank environment - they don't do so well. Repairing & cleaning aircraft capacitance probes is a $100M business. Not many successful avgas capacitance systems - Piper tried with the Malibu & didn't work out, Diamond seems to have a system that performs.
 
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Yep - it was topical to me working on replacing capacitive pennycaps on a Cessna 414
 

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EI makes a neat little electronic fuel gauge that takes a lot of the error out of the system. I don't think it's approved in general, but the Navion guys sell it with paperwork (probably about the only positive they've done since they bought the type certificate).
 
Thinking about what Stewartb said regarding the fluctuating fuel quantities between the resistive float type senders and a digital instrument. Wouldn't it be possible to decrease the hysteresis by adding capacitance to the circuit?
 
Bobbing float arms have always been a problem but digital intruments are so quick to register it amplifies it. I just don't much pay attention to my fuel level instruments in flight. I establish fuel on board prior to departing and I let my FS450 tell me what I've used and what I have left. At most I'll validate that the FS450 fuel remaining somewhat matches the fuel level instruments. Fuel totalizers are a more accurate fuel managemen instrument than qualtity gauges.
 
182driver said:
....................And, maybe I need new bladders. In the 2 wintery months that I had the plane, I usually had gas dripping out of the left wing root down the side of the cabin. I had been filling the tanks quite full - my mechanic says I was overfilling them. When calibrating the EDM-900, I put a measured 38 gallons in each tank (full is 37.5) and the level is still well below where I used to fill to.

My mechanic says just replace the fuel senders and replace the bladers when they leak. I wonder if they already do. Even before I saw the plane, I had budgeted new bladders (aka fuel cells) since they were last replaced in 1999. I'm also a believer in preventative maintenance and fuel leaks sound dangerous and an expensive way to maybe ruin the interior with fuel stains, but then I would not replace the bladders every year. Every 15 years? Especially since the fuel senders need done anyhow?

Is overfilling the tanks even a potential issue? It seems to me that if I put in too much gas, it will come out of the fuel cap or the vent. I cannot think of any reason why fuel would end up inside the wing except for a leak, probably near the top of the bladder.......................
Click to expand...


"my mechanic says I was overfilling them".....wow :) May I suggest you go to the experts. Here is a site that can help you understand what is going on with your leak: http://www.eaglefuelcells.com/ga/tech_tips.html
I had the dreaded fuel stain down the left side of the fuselage and I ended up replacing the bladder. About the time I was getting ready to bring it over to maintenance, the right side did the same. I replaced both bladders.

The original bladders in our C-182P aircraft were well made and lasted a long time. (Mine lasted 30 years). Not so with some manufactured in the 90's. Quality control during manufacture was, shall we say, lacking. By the time I needed new bladders in 2004, the quality had improved. I had one of mine out 2 years ago because of a small leak discovered at the nipple (not the manufacturer's fault, but that is for another story). The cell, now 10 years old look like new. (and Eagle repaired the nipple at no cost to me...other than postal charges).

If you have any questions from someone who has been through it in your type of aircraft, please PM me.

Kevin
 
Stewartb said:
but digital intruments are so quick to register it amplifies it.
Click to expand...

Then the feller that designed it didn't quite understand time constants. In general, you can digitally (or analog-ly) set a smoothing averaging time constant for darn near any value you want. In particular, a 100K resistor and a 500uF capacitor have a time constant (67% of value) of 50 seconds, which should take the "bobbing" of the float out of the equation. Increase the resistor to 1M and you have a little over 8 minutes. The CLEVER designer puts a turn-on circuit in parallel with the time constant to boop (that's a technical term, you'll get used to it) the fuel quantity up to the resting value immediately so you have an instant value when you first turn on the master. jw


.
 
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Thanks for the reply, Jim. I was pretty sure a simple R/C combination would fix the issue.
 
Most digital instruments have a smoothing function or an averaging component. Typical for small aircraft that is a 10 second interval. We can average a sender output up to 16 seconds by altering the programming - we can also output any type of analog signal as well . Stuartb "Floats move up and down" actually they don't really, & I have video. Fuel does move in an aircraft tank and any method of measurement has to accommodate. Good capacitive systems have stand tubes, some good resistive senders have them as well. The stand tube has a small orifice at the bottom and fuel enters into the tube - this stills the internal volume. What isn't recognized is that floats perform a similar function - standing waves wash over the float and the float rides in the trough - biasing the signal down. The issue with traditional float senders is that the wiper on the resistive trace tended to hop to one setting and then when wiper drag was overcome by bouyancy hop to another, A little turbulence and the float would by g force return to another. Friction or more appropriately termed stiction is your culprit here and not the float Floats have very little to do with the issues of a resistance sender. Traditional senders resistance wiper and trace or wire wound format are the primary culprits in bad fuel indication (old analog gauges weren't responsive to these changes) When you add moisture driven corrosion on the resistance wiper - you have a system that goes from bad to worse. We prove every day floats aren't an issue - 15,000 senders fielded - No unscheduled removals
 
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