M20J newly sealed tanks not venting right

[Barzook]

Hi,

First time posting, but always reading. I have had my tanks stripped/sealed by a local shop (I was too far away from Minnesota/Florida vs my experience as a pilot). They had a hard time doing it right, it took many months. I've been flying and fueling the plane for 2 months now and something is not right.

When I fuel it up, I fill it to the edge of the gas cap. So when I put the cap on, it sort of displace some gas, just to give you an idea how full it is. If I come back a few hours later, the fuel level dropped by about 1'' in each tank. Right after fueling, we can hear bubbles making their way to the top of the tank. So if I fill it up and take it as-is the next day, I don't have 32 gallons in each tank but more like 30 gallons probably. Which is a problem for me, I want my full 32 gallons.

What I think happened is that they sealed the upper section of the ribs where there's supposed to be seap-holes to let the air exit in between the tank sections (3 on an M20J per tank, so 2 dividers). There's probably still some openings, so in the end the fuel takes the place of the air and the air gets vented at the top of the tank, but this takes a while.

I think I need to have this reworked to enlarge these holes and would like to have a picture of what it's supposed to look like. That shop will not take the plane anymore, they have had it. So I'd like to document the problem as good as possible to try to find another shop who could do the rework.

Let me know what you think and if you have any pictures of that I'd be very interested too.

Thanks for your help!

[carusoam]

Each rib has several holes at the top and bottom of the ribs…

Air has to move…

as well as fuel has to move through these holes…

If your resealer is unfamiliar with Mooneys…. You probably got the holes filled…

They are easy to look at and clean out…

Otherwise…the fuel is going somewhere else….

don’t trust the useable fuel numbers until you know all of the fuel is actually useable…  

PP thoughts only, not a mechanic…

Best regards,

-a-

[N201MKTurbo]

I'm supposed to help a guy with his tanks this afternoon. they are opened up, I will try to remember to get some pictures.

[Fly Boomer]

4 minutes ago, N201MKTurbo said:

I'm supposed to help a guy with his tanks this afternoon. they are opened up, I will try to remember to get some pictures.

Isn't a certain amount of waiting and wing rocking typical for all Mooneys when trying to get the tanks absolutely, totally, full?

[carusoam]

4 minutes ago, Fly Boomer said:

Isn't a certain amount of waiting and wing rocking typical for all Mooneys when trying to get the tanks absolutely, totally, full?

From the other thread today…

5) When sumping fuel out of a C152… the training was to vigorously sway the plane on the ground… the large motion of the fuel in the tanks would better move water out from its hiding places where gravity could then move it towards the drains…

Ever try to vigorously move a Mooney on the ground?

Try it with an LB full of fuel…

Best regards,

-a-

[Fly Boomer]

3 minutes ago, carusoam said:

From the other thread today…

 

5) When sumping fuel out of a C152… the training was to vigorously sway the plane on the ground… the large motion of the fuel in the tanks would better move water out from its hiding places where gravity could then move it towards the drains…

Ever try to vigorously move a Mooney on the ground?

Try it with an LB full of fuel…

Best regards,

-a-

So what is the procedure for filling the tanks as full al possible?

[carusoam]

Getting air to flow upstream takes a few minutes…

The rib vent holes are pretty small, and the full rate of the fuel nozzle is quite high in comparison…

To load more fuel than ever… find uneven ground…  just remember, you have probably entered test pilot territory with this maneuver… 

Best regards,

-a-

[N201MKTurbo]

8 minutes ago, Fly Boomer said:

Isn't a certain amount of waiting and wing rocking typical for all Mooneys when trying to get the tanks absolutely, totally, full?

With both my F and J you could fill them to the brim and they would stay there.

[Fly Boomer]

Just now, N201MKTurbo said:

With both my F and J you could fill them to the brim and they would stay there.

I don't have any references to cite -- maybe it's the airplanes with Monroy tanks?

[M20F-1968]

There is no substitute for taking the plane to Paul Beck at Oasis/Weep No More in Willmar, Minnesota.  Paul has done some work on location as well.  He may be able to salvage what has been already done, and will give you an honest assessment of the status of your reseal and how to make it right.

John Breda

[A64Pilot]

Two gallons?

Let that dog lie

[N201MKTurbo]

4 minutes ago, carusoam said:

From the other thread today…

 

5) When sumping fuel out of a C152… the training was to vigorously sway the plane on the ground… the large motion of the fuel in the tanks would better move water out from its hiding places where gravity could then move it towards the drains…

Ever try to vigorously move a Mooney on the ground?

Try it with an LB full of fuel…

Best regards,

-a-

Yes, @Eric J's Mooney was trapping water. I showed him how to shake the wings and it got the water out.

Heck, when I was a kid, my friend and I went to the Spruce Goose in Long Beach. I told my friend to grab the tiedown cable on the right wing and when he felt it rise to pull down on it. I went to the other wing and grabbed the cable and pulled down and then let it loose. After about a minute we had it rocking so hard that it was splashing all the water out of the pools the sponsons were sitting in. The wing tips were going up and down about a foot. The security guard came over started laughing, shook his head and walked away.

[N201MKTurbo]

7 minutes ago, Fly Boomer said:

I don't have any references to cite -- maybe it's the airplanes with Monroy tanks?

I know the ones with the flapper on the filler have issues like that. I have flown a few, but don't have a lot of experience with them.

[carusoam]

M20K tanks with Monroys have a complex arrangement of tank locations, forwards and back…and separation from outer to inner tanks…requiring tubing connections…(?)

Probably have a couple of sump drains on each wing to go with that… similar to the pair of fuel caps…

PP fuzzy memories at best… 130g Monroys in an LB are a much more simple geometry…  

Best regards,

-a-

[Fly Boomer]

4 minutes ago, N201MKTurbo said:

I know the ones with the flapper on the filler have issues like that. I have flown a few, but don't have a lot of experience with them.

I have 'em.  I'd love to jettison those things, but I'm not willing to spend a couple of thousand to get rid of them and risk a bogus job.  Seems like half the time when I get something worked on (house, car, airplane), I regret the decision.

[Pinecone]

My K (252) has Monroy tanks.

It takes time to fill it all the way.  I flew last Friday to a nice place for lunch with cheap fuel.  So I wanted to depart with every gallon I could get in the plane (with 2 people, still well below gross). 

We filled the inboard filler on one side, then filled the outboard (Monroy).  Then did the other side.  Then back to the first side to fill the outboard again after the fuel migrated to the inner (original tank).  then back to the other side.  We did one more round, then headed to lunch.  After lunch, we put in another 9 gallons total.

When I calibrated my fuel stick, putting in 2.5 at a time and waiting 10 minutes between each addition, I was able to get 3 more gallons in than it is supposed to hold.  And even with the fuel was just below the outboard filler neck, I could hear air bubbling out of the inboard tank.

I wish the STC included drilling a couple of reasonable size holes to more rapidly transfer the bulk of the fuel from tank to tank.

[carusoam]

 

4 minutes ago, Pinecone said:

I wish the STC included drilling a couple of reasonable size holes to more rapidly transfer the bulk of the fuel from tank to tank.

That STC was successfully transferred recently…

I believe it went to DMax in the end…(?)

 

since the holes are in the rib… the rib’s strength is important…

Making the holes larger… probably has a set of mechanical engineering rules to contend with…

Making more holes… will have a different set of rules… but copying the holes and their separation may make sense…

 

Getting a good answer to this… probably lies between the engineers at Mooney and the brains at DMax…

Probably a five minute discussion amongst those guys could double your air flow rate out of the system…

Proper drilling in a fuel tank environment will take more effort…

PP thoughts only, we have discussed drilling holes in the fuel tank before… M20S long fuel neck challenge with Cris back in 2011….  

Best regards,

-a-

[ArtVandelay]

So what is the procedure for filling the tanks as full al possible?

Fill them slowly, I was able to get an extra gallon or so above spec when I did my JPI calibration using 5 gallon jugs and was filling slowly.

PS, make sure your fuel tank vents are clear.

[Pinecone]

39 minutes ago, carusoam said:

Getting a good answer to this… probably lies between the engineers at Mooney and the brains at DMax…

Probably a five minute discussion amongst those guys could double your air flow rate out of the system…

Proper drilling in a fuel tank environment will take more effort…

PP thoughts only, we have discussed drilling holes in the fuel tank before… M20S long fuel neck challenge with Cris back in 2011….  

Best regards,

-a-

Yeap, but need a couple of bigger holes near the bottom for fuel to move and one bigger one for the air

[PT20J]

My M20J with original factory sealant fills to full capacity rapidly and stays there. I often fill it after a flight and when I come back to the hangar a day or so later, it's still full.

[kortopates]

4 hours ago, Fly Boomer said:

I don't have any references to cite -- maybe it's the airplanes with Monroy tanks?

Rich's tanks are very different than yours. If I remember right, since you don't show model, yours is a K which has the anti-siphon valve. The anti-siphon valve makes it very difficult to add fuel below the bottom of the anti-siphon. Not impossible but its like burping the wings to over fill them. But is by definition over-filling them since "full" at the base of the anti-siphon valve. 

Edited April 12, 2023 by kortopates

[Barzook]

4 hours ago, N201MKTurbo said:

I'm supposed to help a guy with his tanks this afternoon. they are opened up, I will try to remember to get some pictures.

Sounds good let me know! Thanks!

[Barzook]

20 minutes ago, PT20J said:

My M20J with original factory sealant fills to full capacity rapidly and stays there. I often fill it after a flight and when I come back to the hangar a day or so later, it's still full.

That's also what I heard from another M20 owner at my airport and that's the end result I'm trying to achieve! Thanks for your input!

[T. Peterson]

6 hours ago, Fly Boomer said:

So what is the procedure for filling the tanks as full al possible?

I rock my wings with my thigh when approaching full. One hand operating the nozzle and the other keeping the black hose from rubbing the wing leading edge. You can hear it sloshing and bubbling as it drains down. I fill it to just higher than the bottom of the neck.

[Fly Boomer]

2 hours ago, kortopates said:

Rich's tanks are very different than yours. If I remember right, since you don't show model, yours is a K which has the anti-siphon valve. The anti-siphon valve makes it very difficult to add fuel below the bottom of the anti-siphon. Not impossible but its like burping the wings to over fill them. But is by definition over-filling them since "full" at the base of the anti-siphon valve. 

Mine is a 252 with the cursed flappers on the main tanks, so I guess that accounts for the difference.  Thanks.