Thermos Style Gas Cap (1963 M20 D/C)

[Dan Stewart]

I seem some threads here about the Thermos Style Gas Cap, but I'm missing clarity.  I have a 1963 M20D/C and one of the caps does not seal.  Rubber seems too stiff.  Cam seems to work fine still.  With full tanks and on take off, I can visibly see fuel leak out onto the wing.  Does not seem good.  What cap is recommend to replace?  

https://www.aircraftspruce.com/catalog/appages/thermos.php (just for the rubber)

https://www.mcfarlaneaviation.com/products/product/CA27221N/

And do I need to vent (drill a hole) the gas cap before using?

@Raptor05121 you seems to have some posts regarding this, any insight???  

Thanks guys!

 

[Skates97]

10 minutes ago, Dan Stewart said:

I seem some threads here about the Thermos Style Gas Cap, but I'm missing clarity.  I have a 1963 M20D/C and one of the caps does not seal.  Rubber seems too stiff.  Cam seems to work fine still.  With full tanks and on take off, I can visibly see fuel leak out onto the wing.  Does not seem good.  What cap is recommend to replace?  

https://www.aircraftspruce.com/catalog/appages/thermos.php (just for the rubber)

https://www.mcfarlaneaviation.com/products/product/CA27221N/

And do I need to vent (drill a hole) the gas cap before using?

@Raptor05121 you seems to have some posts regarding this, any insight???  

Thanks guys!

 

 

Need to get @Raptor05121 to show up as a link for it to alert him. If you type the "@" and then start typing the name it will start listing names, click the one you want and then it sends them a notification.

Edit: And welcome aboard!

[MooneyMitch]

32 minutes ago, Dan Stewart said:

I seem some threads here about the Thermos Style Gas Cap, but I'm missing clarity.  I have a 1963 M20D/C and one of the caps does not seal.  Rubber seems too stiff.  Cam seems to work fine still.  With full tanks and on take off, I can visibly see fuel leak out onto the wing.  Does not seem good.  What cap is recommend to replace?  

https://www.aircraftspruce.com/catalog/appages/thermos.php (just for the rubber)

https://www.mcfarlaneaviation.com/products/product/CA27221N/

And do I need to vent (drill a hole) the gas cap before using?

@Raptor05121 you seems to have some posts regarding this, any insight???  

Thanks guys!

 

Yes!   I too have a ‘63 D/C model and have replaced the caps.

Currently I’m occupied and don’t have time to access information for purchase for you.  

I’ll provide information later this evening for you.

There is Hope!!  Stand by 

[carusoam]

Welcome aboard, Dan.

As far as venting the cap goes...

Verify that your fuel tank’s vents are working properly... tiny tube mounted on the bottom of the wing...

Expect all Mooney tanks to be vented... eliminating the need for venting the caps to rain above...
 

There are methods of updating your fuel cap system if interested... something to consider if you are resealing them...

 

 

PP thoughts only, not a mechanic...

Best regards,

-a-

[MooneyMitch]

6 hours ago, MooneyMitch said:

Yes!   I too have a ‘63 D/C model and have replaced the caps.

Currently I’m occupied and don’t have time to access information for purchase for you.  

I’ll provide information later this evening for you.

There is Hope!!  Stand by 

The caps shown in the Aircraft Spruce catalogue are exactly what I’ve purchased and are currently indstalled on my plane.

I did not drill any holes in the units. 

[47U]

7 hours ago, MooneyMitch said:

And do I need to vent (drill a hole) the gas cap before using?

If you’re flying in IMC and get into icing conditions, a vent hole in the cap would be a good Idea in case the vent tube on the bottom of the wing ices up.  With the cap vent hole, if the tank is filled to the very top you may experience some fuel escaping on top of the wing.  

Isn’t there a SB on how to drill the cap vent holes?     

Tom

[Greg Ellis]

I have had to replace these more than once in 14 years of owning my airplane.  On my 63 C model, I have tried the ones you show from aircraft spruce and the latch on top is too tall.  The cover door will not close.  

I have tried others (including the piper brand) and even though they fit and would latch closed, for some reason the fuel would still leak.  If I took the rubber part off the new cap and put it on my old cap then they would not leak.  It was very strange.  I ended up going to www.shawplugs.com.  I measured the diameter of the opening to the fuel tank then purchased the snap-tite caps that came pretty close.  I then used just the rubber pieces and put them in my own caps and everything seals very well now.  They do sell just the rubber piece but only in one size.  I did not go that route because it said it was not FAA approved (does not really matter) but it also said it was not approved for volatile liquids and I thought that AvGas may be considered a volatile liquid.  I am pretty sure I went with the 2 inch (50.80mm) version but you may want to measure your airplane to make sure since things could change between airplane models and years.

 

[Boilermonkey]

IS it the rubber not making the seal?  Or do they just need to be adjusted?   If you hold the cap and then rotate the tab at the top it will either tighten or loosen the seal (essentially the diameter that it tries to expand to when closed).

[Raptor05121]

So back in the day when I had this issue, I had to track down a manufacturer and order directly from them. It now seems AircraftSpruce has picked up the gauntlet and now offers them direct, which is nice. I think the first time I had ordered the 2" but there is still a bit of gap and requires the plug to be tight to draw the rubber close so last year I replaced them again and (from the manufacturer) ordered the next size up which I think was 2.25". Its now a smidge tight and you have to angle them to get them from behind the cam-lock tab, but you don't have to draw the rubber so tight to seal.

No you don't have to drill a hole, we have vents inside the scuppers.

If you order those, make sure you screw the new brass tab off and reuse the old one- the new ones interfere with the gas cap door. Or, if you want to use the new ones, take an angle ginder to it and remove the top 1/2" of the triangle that sticks up when its in the locked position.

[Raptor05121]

11 hours ago, carusoam said:

 

There are methods of updating your fuel cap system if interested... something to consider if you are resealing them...

 

-a-

I am not aware of a way to "update" the thermos-style caps on the 48 gallon wings short of cutting into the wing.

[Greg Ellis]

37 minutes ago, Raptor05121 said:

I am not aware of a way to "update" the thermos-style caps on the 48 gallon wings short of cutting into the wing.

I was told this by Don Maxwell a few years ago.  I asked how they could be updated to a newer, more available cap and he said that the skin around the filler would have to be completely removed and replaced with new skin for the new style cap.

[MooneyMitch]

2 hours ago, Raptor05121 said:

Or, if you want to use the new ones, take an angle ginder to it and remove the top 1/2" of the triangle that sticks up when its in the locked position.

+1 

[Raptor05121]

2 hours ago, Greg Ellis said:

I was told this by Don Maxwell a few years ago.  I asked how they could be updated to a newer, more available cap and he said that the skin around the filler would have to be completely removed and replaced with new skin for the new style cap.

That sounds like A LOT of work for 2 more gallons of fuel. Personally, I like the thermos-style. Rainwater drains away as the caps are higher than the scuppers they sit in. Knock on wood, I've NEVER had water in my tanks, even after Florida monsoons.

[cctsurf]

3 hours ago, Raptor05121 said:

ordered the next size up which I think was 2.25

looking at their website, and at mcmaster-carr, they show a 2.125, might that be what you purchased?  Just curious, I'd like to have some on hand if my thermos caps ever die.

[Dan Stewart]

Wow guys, this forum community is awesome!  Thanks for the many responses.  I've had my Mooney for about a year, but was unaware of how great this forum is.   I'm going to try the 2in cap on aircraft source, and just use the rubber (my cam lock is already painted to match the plane).  I'll come back here once installed and let ya'll know how it goes.

 

[MooneyMitch]

1 hour ago, Dan Stewart said:

Wow guys, this forum community is awesome!  Thanks for the many responses.  I've had my Mooney for about a year, but was unaware of how great this forum is.   I'm going to try the 2in cap on aircraft source, and just use the rubber (my cam lock is already painted to match the plane).  I'll come back here once installed and let ya'll know how it goes.

 

My experience...... the tension fit of the cap into the tank filler hole is adjustable with a twist or two of the locking device.

[carusoam]

+1 on the bigger than minor surgery to upgrade to the flush fuel caps...

Even then... keeping water out all the time can be a challenge...

Never skip an opportunity to sump a tank...   
 

PP thoughts only,

-a-

[Raptor05121]

On 9/2/2020 at 2:29 PM, cctsurf said:

looking at their website, and at mcmaster-carr, they show a 2.125, might that be what you purchased?  Just curious, I'd like to have some on hand if my thermos caps ever die.

Yup thats it! Like I said, the metal base is wider so you have to angle it in to get it under the locking tab for the door, but you don't have to screw down the rubber nearly as much to get it to seal.

[cctsurf]

I know that this is an older thread, but I thought this would be of assistance to those in the future with this question:

I just had the experience where the caps would no longer seal on my '62.  I ordered the 2 1/8" caps from McMaster-Carr.  https://www.mcmaster.com/catalog/127/2221/ ,  P/N 

2598K55

 I ordered the zinc plated steel ones because I had no intention of using the metal bits.  Upon arrival, I was quite concerned because they seemed significantly thicker than the originals.  However, back to work...  I was able to unscrew both caps and install the new seals quite easily.  The 2 1/8" caps just slide into the fill holes in my tanks.  Seals like a dream!

[cctsurf]

On 8/21/2021 at 9:40 AM, GEE-BEE AEROPRODUCTS said:

May I have or borrow a original 

I would be happy to send the originals to you if they would be helpful...  They shrunk so that they don't seal neck of the tank, so I am not certain they would be.