Cabin Fuel Smell on Climb-out

[Matt M]

So I have been chasing a fuel smell in my cabin for about 4 months now. It only happens on climb out and goes away in about a minute. I keep my tanks topped off after every flight. When I climb in the airplane no smell of fuel at all just old airplane. I thought I fixed the problem a few weeks ago when I had the fuel pickup tube gasket replaced as it was a little wet around it and had blue staining. Well the last two flights after smell still occurs. It doesn’t happen on subsequent takeoffs which makes me believe that once some fuel burns off the leak stops. Anyhow today I’m climb out no smell at all, until I make a right turn in the climb. So I thought it must be coming from the left side. I switched to the right tank after 15 min or so  I am 3 below full on each side at my destination airport. The next takeoff no smell at all. I go back to my home airport and top off the right and leave the left 3 low. Takeoff again and smell occurs on right climbing turn. I start smelling around and determined it seemed to be stronger toward the right side of cabin. When I landed I pulled off inspection plate under wing leading edge closest to cabin and saw staining on forward part of the tank at the seem where it meets the upper wing skin. It's a 82J with original sealant. It had a repair job about 2 years ago. Different area though. I showed the photo to my mechanic and he thought maybe instead of opening the tank and patching the inside it may be possible to patch on the outside. I am not sure I am too keen on this idea or whether it would even work. I know I probably require a new strip and seal in the future, but it would be nice to get maybe a couple more years. Besides this weep it is dry everywhere else. Thoughts? Also how many gallons low would the tank need to be to reach the top near this seem. It seems like 3 gallons and I have no smell so that is my guess? I think i could live with keeping it 3 low if it buys me more time.

 

Matt

[RobertGary1]

Pretty rare to top off a J or F. That’s nearly 7 hours worth of heavy fuel. 
Probably around 20 gal until the inner wing get to the top. Never really measure it. 

Edited April 20, 2021 by RobertGary1

[mooniac15u]

On 4/17/2021 at 6:00 PM, Matt M said:

So I have been chasing a fuel smell in my cabin for about 4 months now. It only happens on climb out and goes away in about a minute. I keep my tanks topped off after every flight. When I climb in the airplane no smell of fuel at all just old airplane. I thought I fixed the problem a few weeks ago when I had the fuel pickup tube gasket replaced as it was a little wet around it and had blue staining. Well the last two flights after smell still occurs. It doesn’t happen on subsequent takeoffs which makes me believe that once some fuel burns off the leak stops. Anyhow today I’m climb out no smell at all, until I make a right turn in the climb. So I thought it must be coming from the left side. I switched to the right tank after 15 min or so  I am 3 below full on each side at my destination airport. The next takeoff no smell at all. I go back to my home airport and top off the right and leave the left 3 low. Takeoff again and smell occurs on right climbing turn. I start smelling around and determined it seemed to be stronger toward the right side of cabin. When I landed I pulled off inspection plate under wing leading edge closest to cabin and saw staining on forward part of the tank at the seem where it meets the upper wing skin. It's a 82J with original sealant. It had a repair job about 2 years ago. Different area though. I showed the photo to my mechanic and he thought maybe instead of opening the tank and patching the inside it may be possible to patch on the outside. I am not sure I am too keen on this idea or whether it would even work. I know I probably require a new strip and seal in the future, but it would be nice to get maybe a couple more years. Besides this weep it is dry everywhere else. Thoughts? Also how many gallons low would the tank need to be to reach the top near this seem. It seems like 3 gallons and I have no smell so that is my guess? I think i could live with keeping it 3 low if it buys me more time.

 

Matt

Have you checked the seal on your fuel caps?  When I first got my J one of the caps wasn't sealing tight.  When I topped the tank on that side the fuel level would contact the rear part of the cap during a climb and the low pressure on top of the wing would pull fuel out.  I could smell fuel when that was happening and during one flight I could actually see the fuel coming out.  Once I replaced the o-rings and tightened the cap a bit it stopped doing that.

Edited April 20, 2021 by mooniac15u

[Matt M]

2 hours ago, mooniac15u said:

Have you checked the seal on your fuel caps?  When I first got my J one of the caps wasn't sealing tight.  When I topped the tank on that side the fuel level would contact the rear part of the cap during a climb and the low pressure on top of the wing would pull fuel out.  I could smell fuel when that was happening and during one flight I could actually see the fuel coming out.  Once I replaced the o-rings and tightened the cap a bit it stopped doing that.

I replaced those first since that was quick and easy. It's definitely coming out of the top seem on the forward part of the tank. I was just wondering whether my mechanics idea to place sealant on the outside of the tank is really going to do anything. 

[N201MKTurbo]

1 minute ago, Matt M said:

I replaced those first since that was quick and easy. It's definitely coming out of the top seem on the forward part of the tank. I was just wondering whether my mechanics idea to place sealant on the outside of the tank is really going to do anything. 

There is no procedure in the service manual to add sealant to the outside of the rank. It is a bad idea. It is almost impossible to seal a portion of a seam, it will just leak out the ends of the sealant.

The service manual has the procedure for fixing leaks. That is the only approved repair.

[takair]

1 minute ago, Matt M said:

I replaced those first since that was quick and easy. It's definitely coming out of the top seem on the forward part of the tank. I was just wondering whether my mechanics idea to place sealant on the outside of the tank is really going to do anything. 

The inboard side of the tank generally stays near the top longer....so even 3 gallons off the top seems like not enough to drop it there. (But not 100% sure)  It is very possible that the leak is outboard and trickles.  It is difficult to seal from the outside for this reason.  The Mooney Miser (RIP) used to have an STC to repair minor leaks.  Even that was hit or miss if you didn’t know exactly the origin.  Before hiding things with sealant, be sure that is the originating point and not wicking down the lap joints and showing itself there.

[Matt M]

Does anyone know what is the typical success rate and difficuly of a repair on the top forward part of the tank is? 

[RobertGary1]

4 minutes ago, Matt M said:

Does anyone know what is the typical success rate and difficuly of a repair on the top forward part of the tank is? 

If done correctly from the inside the success rate should be 100%. Its a common procedure to patch these tanks; not just for Mooneys but for any wet wing aircraft.

-Robert

[carusoam]

Allow me to throw in a suggestion...

Sure, you may have a fuel leak that you want to get fixed...

 

But,

You are getting fuel aroma during the climb on the first flight of the day....

This is often a symptom of a drop of fuel hitting a warmed surface... in line with the cabin...

 

A common cause for such a drip, a warm surface, and in line with the cabin.... is the engine and its fuel injectors...

FIs are vented... and if not oriented correctly... they can drip...

 

Take a look at each FI, see if there is any blue staining....

PP thoughts only, not a fuel injector aficionado...

Best regards,

-a-

 

[Matt M]

4 hours ago, carusoam said:

Allow me to throw in a suggestion...

Sure, you may have a fuel leak that you want to get fixed...

 

But,

You are getting fuel aroma during the climb on the first flight of the day....

This is often a symptom of a drop of fuel hitting a warmed surface... in line with the cabin...

 

A common cause for such a drip, a warm surface, and in line with the cabin.... is the engine and its fuel injectors...

FIs are vented... and if not oriented correctly... they can drip...

 

Take a look at each FI, see if there is any blue staining....

PP thoughts only, not a fuel injector aficionado...

Best regards,

-a-

 

I'll have to check it out. I thought i found my issue with the seeping tank, but now I am wondering if that is it. I read the issue with the fuel injector. My smell goes away after about a minute which is about around the same time I reduce the MP to 26". Same scenario in the injector venting. It goes in for annual next month so they will have it all apart. Hopefully the root cause is found.

[JimB]

18 hours ago, N201MKTurbo said:

There is no procedure in the service manual to add sealant to the outside of the rank. It is a bad idea. It is almost impossible to seal a portion of a seam, it will just leak out the ends of the sealant.

Actually that isn't 100% true.... It is considered temporary but no clarification on what "temporary" is other than if it it leaks again, you have to clean it and reapply the sealant.

[N201MKTurbo]

But the OP doesn't have fastener leaks.

[KB4]

Try this Gulvit stuff it had a write up in April Mooney Flyer issue and was successful.  

 

[jaylw314]

Don't have any wise words beyond what others have said, but I'd point out that having the smell if you turn right or left doesn't really tell you anything about which side it's coming from, unless you regularly use sustained uncoordinated turns  

[Matt M]

1 hour ago, jaylw314 said:

Don't have any wise words beyond what others have said, but I'd point out that having the smell if you turn right or left doesn't really tell you anything about which side it's coming from, unless you regularly use sustained uncoordinated turns  

Wait is that what those two pedals are for? I have noticed it in straight climb outs before. I was climbing to the right this time. From breaking ground to about 500 AGL I had no smell until I made the initial turn. It was odd. Ball was centered . Seemed like it was from the left, but it's hard to directionally sniff around the plane and fly at the same time. 

[carusoam]

Matt,

There is a Mooney mechanic over at KVAY...

That might be able to help you find the source...

Alan is pretty good with taking Mooneys apart... 

The usual places to look... fuel level sensors, fuel line connectors, fuel tank selector valve...

Some things can be hiding behind the wall coverings...

Best regards,

-a-

[MichiganMooney1]

I hope you have found a solution to this issue. I too have been chasing a very similar issue in my M20E (1964). I get an intermittent smell in the cabin only on a power reduction (like turning base) and dropping the gear. Everything is have inspected is dry. I did see a seepage from my right side fuel sender gasket and replaced it. First flight after that going round the pattern I smelled fuel again. However, all was now dry around the new gasket and everywhere else. Checked all areas on both tanks all is dry with no staining anywhere. This problem is intermittent but always involves a power reduction for landing and lowering the landing gear. The one member who responded with the idea of gas hitting a warm surface is relevant. I may be pursuing that rout soon. Any thoughts? All is appreciated. 

[carusoam]

When lowering the gear… that gives a hint of where the aroma may be coming from…

pattern activity gives a hint of fuel pressing against the seals and rubber connectors….

By the time you can smell the fuel… it is leaving a blue stain somewhere…. Probably very light 

Aroma in the cabin, is often fuel seeping under the rug… at the back of the cabin next to the spar… the floor starts turning blue…

 

Cold weather allows the fuel to travel further before it evaporates…

 

Unfortunately, even flying a Mooney slowly… a drip of fuel can evaporate and spread really far…

Pp thoughts only….

-a-

[Matt M]

On 1/17/2022 at 8:08 PM, MichiganMooney1 said:

I hope you have found a solution to this issue. I too have been chasing a very similar issue in my M20E (1964). I get an intermittent smell in the cabin only on a power reduction (like turning base) and dropping the gear. Everything is have inspected is dry. I did see a seepage from my right side fuel sender gasket and replaced it. First flight after that going round the pattern I smelled fuel again. However, all was now dry around the new gasket and everywhere else. Checked all areas on both tanks all is dry with no staining anywhere. This problem is intermittent but always involves a power reduction for landing and lowering the landing gear. The one member who responded with the idea of gas hitting a warm surface is relevant. I may be pursuing that rout soon. Any thoughts? All is appreciated. 

Turned out to be the fuel cap. I found a small blue trail leading from the back of the cap. There was a little play in the cap which caused a small gap toward the rear of the cap. When I topped the tanks the negative pressure sucked the fuel out. Once the fuel dropped a bit no more smell. New o rings and tightening up the caps resolved the problem.

[Browncbr1]

1 hour ago, Matt M said:

Turned out to be the fuel cap. I found a small blue trail leading from the back of the cap. There was a little play in the cap which caused a small gap toward the rear of the cap. When I topped the tanks the negative pressure sucked the fuel out. Once the fuel dropped a bit no more smell. New o rings and tightening up the caps resolved the problem.

I’m not sure how you could smell fuel coming out of the caps in flight.   Your symptom sounds like a small leak somewhere on the leading edge of one of the fuel cells.  It runs down the edge sometimes missing the drain hole and goes to the root where it’s open to the cabin.     The upper leading edge is prone to leak on mine at fill up also. I usually store in hangar with fuel around tabs because of this. 

[carusoam]

+1 for finding fuel leak when tanks are topped…

usually a heat related failure after decades…

Often, the staining inside the wing gets found at annual…

PP thoughts only,

-a-