'48 Fuel Cap Overflowing/Uneven Fuel Burn

[drew.fultz90]

All,

Lately I have noticed fuel stains on the right wing and fuel puddling in the top of the right wing fuel cap. Especially when the tanks are full. I was flying with a buddy the other day and as I entered a turn below him, he told me he noticed fuel spraying off my right wing while in the turn.

Today, I topped off my tanks and made a 1.8 hour trip. I checked the wings and sure enough, fresh fuel stain on top of the right wing and a slight puddle of fuel in the top of the cap. I checked my fuel in both tanks. I had about 15 gals in the right tank and 1-2 gals in the left tank. By my calculations that shows about 11.4 gals/hr burn which I know is not right. I have previously recorded about 8.5-9 gals/hr on another trip. This tells me that over the 1.8 hours today, I lost approx. 4 gals! I checked my fuel cap gaskets and they do need replacing, but is there more going on here? Can leaky gaskets really lose that much fuel? Are these caps supposed to have some sort of check valve in them or not? If I have to, can I even replace these caps?

It seems to me that it is similar to the situation posed here: viewtopic.php?f=24&t=5136

Thanks,

Drew
Starkville, MS
'48 N4179V

[GAHorn]

Beside the gaskets the current version of fuel caps have a red-rubber check-valve/flap in the center of the lower cap. This is to allow air to enter the tank and is supposed to prevent fuel spraying as you describe. You should inspect that carefully.

[sfarringer]

Beside the gaskets the current version of fuel caps have a red-rubber check-valve/flap in the center of the lower cap. This is to allow air to enter the tank and is supposed to prevent fuel spraying as you describe. You should inspect that carefully.

George, you may have forgotten that '48 fuel tanks use an entirely different cap arrangement.
(Unless I have missed out on an updated '48 fuel cap!)

[GAHorn]

Beside the gaskets the current version of fuel caps have a red-rubber check-valve/flap in the center of the lower cap. This is to allow air to enter the tank and is supposed to prevent fuel spraying as you describe. You should inspect that carefully.

George, you may have forgotten that '48 fuel tanks use an entirely different cap arrangement.
(Unless I have missed out on an updated '48 fuel cap!)

Well....DOH!,,,, I completely overlooked the Title of the thread!
Thanks for straightening me out.

[brianm]

I had a very similar issue a couple of years ago with my '48. Took off on a cold morning with full fuel. About 45 minutes into the flight my girlfriend/copilot says "hey, is your left fuel gauge broken?" It was reading zero, right tank was reading full. We landed about 5 minutes later at the nearest airport. The left tank was completely empty, the right wing had a big blue stain and the tank was so full it overflowed when I removed the fuel cap. The local mechanics very kindly put aside some much better paying work to help troubleshoot. We suspected the gasket on the right tank but couldn't see anything wrong with it. After the airplane warmed up for about an hour we put a thin coating of Parker Fuel Lube on the left and right gaskets. I can't say that that was the cause or solution, but 2 years later I'm using the same gaskets and the issue has not reoccurred. My best guess is that the very cold weather made the gaskets stiff and during the preflight the right gasket didn't seat correctly and the low pressure was able to not only suck fuel from the right tank overboard, but pull it across from the left tank.

[Poncho73]

My 48 had the same issue. It leaks through center pin. I disassembled both caps, cleaned them thoroughly rotated the large rubber gasket, applied some fuel lube. I added a small ORing between shaft and washer. This cured the shaft leak. I’d send a pic but I can post using my IPad

[c170b53]

Crop your picture then send it to yourself by mail and crop it again to fit within the dimensions required for upload attachment. Seems to work for me.

[dstates]

I’d send a pic but I can post using my IPad

When you add a picture with your iPad you can choose the size to upload. See the images below. First select to upload an image from your Photo Library. Once you select one, touch the size shown at the bottom of the image, then you can select the size. Large has always worked for me.

[3958v]

If your gasket or the small O-ring does not seal gas will be sucked out of the fill cap and gas will be sucked over from the other tank because the cap is In a low pressure area of the airfoil. Same thing happens if you forget to put a cap on. The tank that shows a high fuel burn by the gauge is the one with the cap on. I know this because someone told me Bill K

[Poncho73]

I’d send a pic but I can post using my IPad

When you add a picture with your iPad you can choose the size to upload. See the images below. First select to upload an image from your Photo Library. Once you select one, touch the size shown at the bottom of the image, then you can select the size. Large has always worked for me.

CA339BA2-379C-4134-A570-080D271DE100.jpeg

BA36BD91-3E84-4E8F-AF10-98DFFBE371E3.jpeg

I don’t have an option to upload a pic when I reply. Not sure why, but there is no upload image option.

[c170b53]

use that tab to start the process. You may have to crop the width of your photo a bit to fit (within iphoto) your pictures then choose file then chose place in line. Should work.

[Poncho73]

I only have the option tab

[Bruce Fenstermacher]

I only have the option tab

Look again. Your forum privileges were fouled up. Fixed now.

[Poncho73]

I only have the option tab

Look again. Your forum privileges were fouled up. Fixed now.

My hero Bruce......Thanks

[Poncho73]

here we go, I installed an oring between the lower cap surface and washer. fuel lube helps as well.