Fuel starvation?

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C_Parker

Pre-takeoff checklist
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Guys, I'm having a tough time with a weird and intermittent issue. I can't be sure, but it seems to only happen right after fueling with full tanks. I've never experienced it with partial fills and it seems to bounce back after the fuel levels have dropped. Cessna 182F, which is single vent, and standard fuel caps.

With full fuel, usually within the first 15-20 minutes of flight, my EGT's will climb, the engine will start to run rough, and just generally act as if it's starving of fuel. It lasts for a couple of nerve racking minutes and then clears up. Fuel burn is lopsided, with only the left tank indication fuel consumption and then after an hour or so of flight the fuel levels even out.

My IA has gone through the vents, and properly positioned the single underwing vent, but it's still doing it. He did find that the vent tube over the head liner was sagging, he fixed that, and it helped with really lopsided fuel burn that was going on all the time, but the starvation still happens and does the lopsided burn early in a flight.

I have 30 gallon fiberglass fuel tanks. The only thing I can think of is maybe somehow I'm overfilling? Everyone I ask gives me a different opinion of what "full" is. There is a slash cut tube on the fuel neck, I fill to the bottom of the tube.

Any ideas?
 
Never understood topping planes off, especially something like a 182, I mean who wants to sit in it for that long? And at the expense of performance?

I have never topped my plane off in the few years I’ve owned it, I just fuel for the mission plus reserves, though I do go with 1hr reserves

But off the cuff sounds like you’re filling it too high

Maybe try new vented caps?
 
I wonder if flying it around for a while without using the both setting on the fuel selector would reveal anything. Maybe take off as usual in both, and cruise 20 minutes out of each thank, see what happens?

Full fuel to me means that when I put the cap back on, fuel gets pushed out. Plus one on the partial fill for performance. I've never been able to get my bladder past the 3hr mark.
 
C_Parker said:
Guys, I'm having a tough time with a weird and intermittent issue. I can't be sure, but it seems to only happen right after fueling with full tanks. I've never experienced it with partial fills and it seems to bounce back after the fuel levels have dropped. Cessna 182F, which is single vent, and standard fuel caps.

With full fuel, usually within the first 15-20 minutes of flight, my EGT's will climb, the engine will start to run rough, and just generally act as if it's starving of fuel. It lasts for a couple of nerve racking minutes and then clears up. Fuel burn is lopsided, with only the left tank indication fuel consumption and then after an hour or so of flight the fuel levels even out.

My IA has gone through the vents, and properly positioned the single underwing vent, but it's still doing it. He did find that the vent tube over the head liner was sagging, he fixed that, and it helped with really lopsided fuel burn that was going on all the time, but the starvation still happens and does the lopsided burn early in a flight.

I have 30 gallon fiberglass fuel tanks. The only thing I can think of is maybe somehow I'm overfilling? Everyone I ask gives me a different opinion of what "full" is. There is a slash cut tube on the fuel neck, I fill to the bottom of the tube.

Any ideas?
Click to expand...

Maybe all of the ‘sag’ wasn’t taken out of the connecting vent.
 
C_Parker said:
Guys, I'm having a tough time with a weird and intermittent issue. I can't be sure, but it seems to only happen right after fueling with full tanks. I've never experienced it with partial fills and it seems to bounce back after the fuel levels have dropped. Cessna 182F, which is single vent, and standard fuel caps.

With full fuel, usually within the first 15-20 minutes of flight, my EGT's will climb, the engine will start to run rough, and just generally act as if it's starving of fuel. It lasts for a couple of nerve racking minutes and then clears up. Fuel burn is lopsided, with only the left tank indication fuel consumption and then after an hour or so of flight the fuel levels even out.

My IA has gone through the vents, and properly positioned the single underwing vent, but it's still doing it. He did find that the vent tube over the head liner was sagging, he fixed that, and it helped with really lopsided fuel burn that was going on all the time, but the starvation still happens and does the lopsided burn early in a flight.

I have 30 gallon fiberglass fuel tanks. The only thing I can think of is maybe somehow I'm overfilling? Everyone I ask gives me a different opinion of what "full" is. There is a slash cut tube on the fuel neck, I fill to the bottom of the tube.

Any ideas?
Click to expand...

You should have a flapper type valve that works to prevent fuel from existing the vent and allows air to enter for to prevent negative pressure. I would start there.
 
Eric Stoltz said:
I wonder if flying it around for a while without using the both setting on the fuel selector would reveal anything. Maybe take off as usual in both, and cruise 20 minutes out of each thank, see what happens?

Full fuel to me means that when I put the cap back on, fuel gets pushed out. Plus one on the partial fill for performance. I've never been able to get my bladder past the 3hr mark.
Click to expand...

That might tell a story. Flying on both but uncoordinated, ball to one side first for about 20 minutes, refuel and then the other side might reveal something.
 
Eric Stoltz said:
I wonder if flying it around for a while without using the both setting on the fuel selector would reveal anything. Maybe take off as usual in both, and cruise 20 minutes out of each thank, see what happens?

Full fuel to me means that when I put the cap back on, fuel gets pushed out. Plus one on the partial fill for performance. I've never been able to get my bladder past the 3hr mark.
Click to expand...

Eric, this is a good point that I forgot to mention. I switch tanks back and forth during these episodes, again I'm a bit tense when it happens, but if I switch to the right tank it always seems to make it worse. Switching to the left tank doesn't seem to make a difference. I have to stress the point that this data is shaky at best.
 
Lachlan said:
Vented fuel cap needs a quick overhaul. ;) Pulling a slight vacuum on the full tanks til the big vent is uncovered, and your vented cap gasket has stiffened up and can’t keep up with the fuel burn.
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This is the mostly likely culprit.

Checking all the vents and forgetting the vent in the fuel cap itself is very common.
 
C_Parker said:
Eric, this is a good point that I forgot to mention. I switch tanks back and forth during these episodes, again I'm a bit tense when it happens, but if I switch to the right tank it always seems to make it worse. Switching to the left tank doesn't seem to make a difference. I have to stress the point that this data is shaky at best.
Click to expand...

Left tank is the only one directly connected to the underwing vent. There’s a tube that runs from right to left that vents the right, but when the tank is full, that vent line is submerged, so all it’ll do is transfer fuel across until it unports.

The vent in the fuel cap is supposed to suck open for air during this time.

It’s the caps. Overhaul the rubber vent in the caps so they aren’t stiff and open properly.

While you’re at it, if the cap vents were neglected the rubber hoses going from the tanks through the gap in the wing root are also probably hard as a rock and rotten.
 
Sometimes people replace fuel caps with one that might not contain a vent or be approved for your plane ... caught that on a rental years ago ...
 
The cap vent valves are silicone and don't stiffen up. They will sag and let water in, though. More likely are worn/hardened/cracked fuel cap gaskets letting the low pressure boundary layer put vacuum on the tank. The fuel cap vent is designed to negate that and allows static pressure in if the cap gaskets are ok.

I'm not convinced it's a fuel issue, either.
 
Lachlan said:
Vented fuel cap needs a quick overhaul. ;) Pulling a slight vacuum on the full tanks til the big vent is uncovered, and your vented cap gasket has stiffened up and can’t keep up with the fuel burn.
Click to expand...

You bring up a valid point, I believe the 182F only has 1 vented cap and it is supposed to be on the side opposite the vented tank. Op, are the gas caps switched?
 
Clip4 said:
You bring up a valid point, I believe the 182F only has 1 vented cap and it is supposed to be on the side opposite the vented tank. Op, are the gas caps switched?
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The AD that mandates vented caps stipulates either one on the right tank, or on both tanks. Most were long ago converted to two vented caps. Can't buy non- vented caps anymore.
 
Ok so I replaced the cap on the right tank tonight. I can't be totally sure, but the diaphragm on the cap seamed like it was lightly crusted down. That probably fixed it if there was a problem but I didn't want to risk it so I still replaced the whole cap.

I'm leaving on a 1200 mile cross country tomorrow, if it's going to happen again it will tomorrow. Crossing my fingers.
 
Aaaaaand of course on the third leg of the journey it happened. Since replacing the cap my super-lopsided fuel burn in the first hour is gone, but right at 3/4 tanks indicated at 11,500 MSL cruising along in smooth air my EGT's began to climb. I did nothing but run the mixture in and rock the wings and it dropped right back down. I'm baffled.
 
C_Parker said:
Aaaaaand of course on the third leg of the journey it happened. Since replacing the cap my super-lopsided fuel burn in the first hour is gone, but right at 3/4 tanks indicated at 11,500 MSL cruising along in smooth air my EGT's began to climb. I did nothing but run the mixture in and rock the wings and it dropped right back down. I'm baffled.
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Intake manifold leak? EGT going up would be not enough fuel or too much air...

With the knowledge that both caps are for sure working and gravity hasn’t stopped, last I checked anyway... fuel is getting down from the tanks unless there’s a blockage somewhere.

Fuel selector valve is suspect in that chain, as is the carb itself needing work, and the intake manifold.

Oh. One more thing. What temp and humidity? Did you try carb heat? I’ve had the carbed O-470 at altitude ice up before. Pull carb heat, massive cough as the engine ingests a blob of water and all back to normal.

Just brainstorming here.
 
Thanks, denverpilot!

I know for a fact that my fuel selector valve is leaking in the off position. I’m not sure if that would cause any intermittent fuel interruption while on “both,” but it is a known defect. I’m going to replace it with a brand new McFarlane valve now that they’re approved for the 182.

The carb was replaced about 100 hours ago. But obviously that doesn’t rule out an issue.

Every time this has happened it’s been at high altitude. I’m not sure if that’s just an artifact of time in flight since I almost always cruise high, or what.

I have tried carb heat (followed the power loss in flight procedure) at least twice and I don’t recall it helping at all. At 11,500 today it was about 42*F and humidity was high. It’s happened above and below freezing temps. The 470 is an ice maker for sure, next time it happens I’ll start with carb heat to verify.

This time I literally just rocked the wings. I don’t have the balls to do nothing and see what happens, but it would be interesting to know what would happen.

The left cap is still an old one though, I’m going to order a replacement since I’m basically at a shotgunning approach at this point...

I’m thinking that when I get back I need to have my A&P just rip all the fuel and vent lines apart and IRAN each one.
 
We kinda got lucky on ours. One of the lines started leaking down the INSIDE of the front pillar during steep turns — which told us they were all cracking and hard. So we replaced em all. Was a bit of a surprise to see blue stuff inside the cabin. Happened a long time ago.

Then there was the inevitable hunt for uneven fuel burn in Cessnas which we chased pretty hard with info from CPA and learned it’s always a thing but you can make it “better”.

Then the bladder let go in the hangar, so that got replaced along with a nice Eagle fuel drain a million times better than the factory drains...

It never ends with keeping 60s and 70s machines operating correctly, but from watching folks with newer ones, they don’t seem to have any better luck for long. Ha. Same designs, same problems. Age is against us on these older ones, but we replace stuff and they behave as well as the newer ones for a while again. :)

All in all, at least it’s a 182 and parts aren’t unobtainium or outreageously expensive other than the usual aviation 400% mark up over the same thing at NAPA. Hahahahaha.

Sorry you have to chase it. Our other big chase years ago was the flipping voltage regulator. We of course shotgunned in some other things until we did proper troubleshooting. But we’ve seen some folks chase that one longer and harder. Ha.

Life with an airplane. :)
 
Remember that about 90% of engine troubles are electrical, not fuel-related. A malfunctioning magneto can drive EGTs crazy, too.
 
Hmmm.... can you guys elaborate on that? How does altitude effect the magnetos?

If ignition was poor, would that cause lower EGTs? Unless we’re talking timing?

How would rocking the wings effect the magneto?

Also what does the alcohol do?
 
C_Parker said:
Hmmm.... can you guys elaborate on that? How does altitude effect the magnetos?

If ignition was poor, would that cause lower EGTs? Unless we’re talking timing?

How would rocking the wings effect the magneto?

Also what does the alcohol do?
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Magnetos misfire at altitude because the air is thinner, meaning it’s not as good of an insulator down low. If a mag is “iffy” it’s most likely to have sparks jumping where they shouldn’t at altitude. Disassembly will usually find burn marks inside where the spark is jumping across the mag. How old are yours?

Rocking the wings... bad plug wires?

He’s suggesting the alcohol to remove/grab any water in the tanks.
 
If you have a fuel selector that is leaking regardless of position the aircraft should be removed from service. If that selector is allowing air into the fuel system it could be your problem.
 
The right mag was just inspected, my mechanic couldn’t get the screws to come loose on the left mag. Not sure if it’ll come apart if he tries a little harder or if the whole mag needs to be replaced. For what it’s worth, the right mag was in excellent condition when he inspected it.
 
The fuel valve leak is an internal leak, it just leaks a little bit if fuel past in the off position.
 
C_Parker said:
The right mag was just inspected, my mechanic couldn’t get the screws to come loose on the left mag. Not sure if it’ll come apart if he tries a little harder or if the whole mag needs to be replaced. For what it’s worth, the right mag was in excellent condition when he inspected it.
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Hours in service the same on both in the logs?
 
Actually I'm not entirely sure, but I believe so. Has was performing a 500 hour inspection on the mags.
 
I posted another thread in the maintenance section to see if anyone had any experience with stuck screws so hopefully I can get it inspected without dropping $1k on it for a new mag. This issue is getting really expensive :eek:
 
C_Parker said:
Also what does the alcohol do?
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Isopropyl will absorb the water, if any, and mix with the gas without separating the tetraethyl lead from the gas, and burn it through the engine. Old bush pilot trick.

I don't really think water in the tank is causing your problem, just a cheap way to eliminate one step.
 
Jeff767 said:
If you have a fuel selector that is leaking regardless of position the aircraft should be removed from service. If that selector is allowing air into the fuel system it could be your problem.
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Can't happen. It's an old 182 with a carburetor and is gravity-feed all the way. There is never any negative pressure on the fuel system that could suck air in past a leaking fuel valve.

The leak he has is past one of the seals inside the valve so that it passes a bit of fuel when it's shut off. The carb's float valve will stop the flow, so it only shows up when the strainer is disassembled for cleaning. The danger is that the fuel can't be totally shut off if there's a fire in flight. And it's a sign that the seals in the valve are old and might start crumbling and cause further trouble. The valve is easy enough to overhaul, but the tanks have to be drained first. A big pain.

Mentioning the strainer brings to mind the carb's inlet filter. It's a fine screen in the carb's inlet fitting that a lot of mechanics overlook, and it should be checked at least annually.

And the suspicion around venting also brings to mind the fact that certain bugs build sticky nests inside pitot tubes and fuel tank vents, blocking them completely. One of the things Cessna has on their inspection checksheets is a check of that vent tube to see that it's open and that the vent check valve is working right.


Wondering some more: A leaking fuel valve. If someone ran mogas with ethanol in it, the seals in the valve might be swollen and restricting the flow, not just failing to seal it off.
 
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Guys my fuel selector was rebuilt but started leaking immediately after. I'm thinking the body of it is compromised, which is why I'm ordering a new mcfarlane fuel selector not that they're approved for the 182. Super expensive, but it'll outlast me.

The concern about ethanol is valid, the plane has an STC for mogas, but I've never taken advantage of it.
 
Not a likely explanation, but I had a similar problem in our C206 that occurred around the time that the fuel bladders started leaking. The fuel dissolves some of the adhesive on the tape placed internally over seams in the wing and starts exuding a green goo near the drain valves on the wing. On a flight over mountainous terrain in NH I had the engine essentially stop, then start about 8 seconds later, then stop for another 5 seconds or so and repeat those steps a few more times before it ran normally again. A thorough inspection at the destination turned up nothing in the fuel or electrical system that would explain the problem. We replaced the fuel bladders and in the next 200 hours or so have had no recurrence. (The JPI 830 logs might have helped, but that data was not retrievable, and we had to send that out for repair as well.)

It's hard to explain how green goo on the outside of the bladder would get inside the bladder, but if it did it's quite possible that it migrated into the fuel lines and dissolved after temporarily blocking them.
 
dbahn said:
On a flight over mountainous terrain in NH I had the engine essentially stop, then start about 8 seconds later, then stop for another 5 seconds or so and repeat those steps a few more times before it ran normally again.
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Zowee..!! How long did it take for your heart to run normally again.??
 
Opened left tank and found this
 

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