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Fuel smell in cockpit


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I fly a 63 C model and I have absolutely no fuel smell in the cockpit so in my case any smell is a cause to stop and make sure everything is okay.  I have had fuel odor in the cockpit before but that was due to two very bad things happening.  One was a fuel leak from my left fuel tank.  They are notorious for leaking into the interior behind the pilot's seat.  You will see blue stains on the carpeting.

 The second was something very unusual.  I was flying home one afternoon and got a tremendously strong fuel smell in the cockpit.  I mean it was very bad.  Giving me a headache, etc...  I was a few minutes from home so I landed.  The next day I flew the plane to my mechanic at the time.  On that flight there was only a slight fuel smell.  While trouble shooting the problem it was discovered that there was a metal fuel line coming into the cockpit down near the pilot side rudder petals.  When the mechanic turned on the fuel pump, fuel started pouring out from the firewall in this area.  When looking down by the rudder pedals fuel was pouring into the cockpit.  The mechanic was able to remove the metal line.  Over the years vibrations in the metal tube had worn a thin slit in the tube where it was vibrating against the firewall.  There should have been a protective grommet there but it was not in place.  So over the years it just made a nice narrow slit in the metal tubing and eventually broke through allowing fuel to leak into the cabin. 

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Double check what you are smelling.  I was flying a Cherokee once and got a sudden strong smell that was almost-but-not-quite like fuel.  Turns out it was a blown brake master cylinder, and it had leaked hydraulic fluid all over the floor.  If you've never smelled hydraulic fluid, take a whiff so you can distinguish it from fuel.  Obviously that is less worrying (but messier and smellier) than a fuel leak.

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Could turbulence cause it? I flew through two hours of some of the toughest turbulence in my life two days ago in the southwest.


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I’ve never seen turbulence cause a fuel smell in the cockpit (this coming from someone who has owned the same Mooney for 27 years).

If I have smelled it in the cockpit, it is almost always been the fuel sender gasket.

If you have wet wings and not bladders, a leaky fuel cell could cause it smell near the wing root.

Sender:

3c9ffe390cb6441327596fd7d7ecf289.jpg




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I have the same issue, it was a small leak in the fuel selector switch, as well the dukes electric pump is dripping a small amount of fuel when turned on. Electric fuel pump and selector switch are being overhauled. Good places to check and eliminate from the list of culprits, blue stains tell the story.

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If the origin was a leaky fuel sender gasket, it would seem that you would smell fuel even when it is on the ground hangared.  

Likewise, hangar rhe plane, let it sit for a few days, then turn the electric fuel pump on for a few seconds.  The fuel smell should return.

John Breda

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Was that momentary? Or did it last? Is it there while on the ground?

M20Cs always smell like fuel.... (not really)

Until they get loved by a new owner....

Or they get into a forever plane ownership situation...

Fuel aromas come from several places...

Most, are noticeable when you open the cockpit door...

By the time you smell the aroma twice.... there is a blue stain somewhere recording it’s location...

Turbulence can be a factor... so can steep turns... so can full fuel tanks...

Lift the rug under the back seat.  This is the place my M20C liked to store excess fuel...  the brown rug was slowly turning blue.

There are two simple locations that like to leak.  Easy to fix...

  • Fuel sender seals...
  • fuel line rubber hose connector...

Less simple places may be related to fuel tank sealant... how old is your sealant?

These are old rubber or cork materials that have been updated in design since the early years...

A really interesting learning experience comes from removing the interior panels at the wings...

You will find some things that can be cleaned, updated, or sealed....

There are no normal fuel smells when flying an M20C... :)

PP thoughts only, My M20C was unloved for years before I got her...

Best regards,

-a-

 

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carusoam, your wisdom continues to amaze, astound, and inspire.   Having just completed the panel redo and EDM900 install, the fuel smell in my C on the ground is really starting to annoy me.   It is present even when the tanks are below the level where they weep, especially on the pilot's side.  I don't notice any blue carpet.  Is there some document, previous thread, or web page explaining how to remove the interior panels without destroying them?   How does one gain access to the fuel pump/gascolator?   I have manuals but have not begun to study the issue.   Your response to this thread prompted me to ask.  -Thx.

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3 hours ago, Fred_2O said:

carusoam, your wisdom continues to amaze, astound, and inspire.   Having just completed the panel redo and EDM900 install, the fuel smell in my C on the ground is really starting to annoy me.   It is present even when the tanks are below the level where they weep, especially on the pilot's side.  I don't notice any blue carpet.  Is there some document, previous thread, or web page explaining how to remove the interior panels without destroying them?   How does one gain access to the fuel pump/gascolator?   I have manuals but have not begun to study the issue.   Your response to this thread prompted me to ask.  -Thx.

I have taken my interior out too many times to count. I am not sure on your 67 how much is different, but it typically requires to take the window treatments down first. Once they are removed, it is much easier to remove the seats and then remove the screws that hold the side panels. If you want to go even simpler, install the Spatial Designs side panels. Then you are just pulling on hook and loop fasteners, no screws.

 

DSC_4319.JPG

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In my 65C a few sheet metal screws held the interior together...

The tubes have a couple of pieces of sheet metal attached (ears?) that are for landing the screws....

If you have the original fabric wall covering, the bottom of the grayish, brownish, panel may also turn blueish....

You really want to get behind these panels to see that the old insulation is not there.

When you get back there and the insulation is gone,  look for where some aluminum tape would help to block the OAT from becoming IAT. :)

Expect lots of cleaning can be done...

There we’re a few things going through that area that needed some help...

  • fuel line connector, rubber hose.
  • Fuel level sender, cork seal.
  • Low pressure brake and flap hydraulic oil return, rubber hose.

If yours are original they may look bubbly, cracked, and brittle... generally old and falling apart...

My M20C was possibly the oldest uncared for airplane for sale the day I got her...

As for the fuel gascolator... that’s under the floor boards, accessible from the other side.  Have a plan at annual time to review all of that.  Lasar has the parts so you can be ready for that...

Hoping this is helpful...

PP thoughts only, not a mechanic...

Best regards,

-a-

Man, those spatial panels look nice... :)

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On 4/5/2018 at 12:21 AM, M20C_AV8R said:

I have the same issue, it was a small leak in the fuel selector switch, as well the dukes electric pump is dripping a small amount of fuel when turned on. Electric fuel pump and selector switch are being overhauled. Good places to check and eliminate from the list of culprits, blue stains tell the story.

Who overhauls those components? I have a dukes boost pump that’s leaking 2 drops a minute and sometimes fuel comes out the selector when the ring inside is pulled, and sometimes it doesn’t (both tanks)

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59 minutes ago, N6018Q said:

Who overhauls those components? I have a dukes boost pump that’s leaking 2 drops a minute and sometimes fuel comes out the selector when the ring inside is pulled, and sometimes it doesn’t (both tanks)

Aeromotor is who we are using, $450 plus I take care of the shipping both ways for my pump

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46 minutes ago, carusoam said:

Lasar has the parts for the leaky fuel selector...  it will leak no matter which tank is selected.  It will also leak air into the fuel line...

Something you want to get OH’d...

PP thoughts only, not a mechanic.

Best regards,

-a-

Actually it’s my pump that’s leaking, not my fuel selector. I just noticed while I had some help, that sometimes when my pull ring inside the cockpit is pulled fuel comes out the bottom drain and sometimes it doesn’t. Tried with the selector on both right and left tanks with the same results.

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The inside should not smell like avgas, period.

I'd start by checking for fuel leaks visible externally (front and rear spar), then pull the small, most inboard inspection panels under the leading edges of the wings and checking for fuel there. That is just to see if you have a tank leak that might be migrating into the cabin. Those will only take you a few minutes. If that isn't fruitful, start pulling interior until you get it figured out.

Edited by Immelman
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On 4/6/2018 at 12:54 PM, RobertGary1 said:

Just pull the interior panels back and look. It will be super obvious if you have blue staining. The fuel selector leaking is pretty common and a pretty easy fix.

 

-Robert

Also remember that your wing leading edges are in continuity with your fuselage by your knees.  Any fuel from forward seam or inspection panel will migrate forward and you'll smell it there.  Fuel selector leaking is another common place. The senders have been discussed.   A more urgent fuel smell diagnosis would be from your panel fuel pressure gauge - put your finger behind there to see if there's any blue dye or wetness - the danger there is fuel near electronic equipment.  Use your nose.  

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I had this issue last year in my M20E. Actually it was the occasional passenger that alerted me as my sense of smell is really poor. At Annual we discovered the gasket on the gasolator was completely shot. It's replaced now. Consider myself lucky. It signs of gas leaks will be investigated ASAP from now on!

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  • 2 weeks later...
On 4/28/2018 at 9:29 PM, BigD said:

Thanks everyone for your help. The smell is gone. I’ve flown another 15 hours aroma free. This is a great resource!

I've not gotten to digging for the source of my smelly "Mooney sweat".   Been too busy flying.   When it is moving through the air, the fuel smell goes away.   What did you do exactly?

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