Dark Blue Fuel

If I leave my RV-7A sit for a few days, when I sump the left tank, I get a very dark blue fuel. Only for one sump. If I sump it again right away, I get the traditional lighter blue-colored fuel. It is almost as if the dye is settling out of the fuel at the sump point.

Has anybody else experienced this? Does anybody have any clues as to what might be happening?

Two thoughts........

If that drain has a very slow leak, you could be seeing the dye that is left over after the fuel evaporates from the leak.

Or, something inside the tank is dissolving slowly......any weeping rivets?

I've seen this on my -6 occasionally, as have others with other aircraft in my area. It seemed to happen about the same time for everyone, which made us all think it was correlated to a batch or two of fuel, that may have received extra colourant.

The drain does have VERY SLOW leak, like a drop every 5 minutes. So, Mike S. suggestion seems possible. No weeping rivets.

Snowflake, I thought about your suggestion also, but would think, if the entire fuel batch was darkened, my fuel sump would not return to normal after just a half tube sump.

I had a similar situation on my Grumman which was due to a very slow leak. So I suggest you replace your drain valve and see if that fixes the issue.

macrafic said:

The drain does have VERY SLOW leak, like a drop every 5 minutes. So, Mike S. suggestion seems possible. No weeping rivets.

Snowflake, I thought about your suggestion also, but would think, if the entire fuel batch was darkened, my fuel sump would not return to normal after just a half tube sump.

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You can remove the drain valve and clean/repair it without draining the tank. Have a spare drain valve handy (or a 1/8" NPT pipe plug) while standing next to the leading edge of the wing. Loosen the drain valve to the point where it is about to fall out then quickly pull it free, hold a finger over the hole, then quickly remove the finger and insert the plug. Very little fuel (3-4 ounces?) will be lost. Don't do this while lying under the wing unless you want an armpit full of fuel....

Most likely there is a very small piece of trash trapped under the drain valve o-ring.

One more vote for the leaking drain fitting concentrating the blue dye. Easy to fix as has already been described.

Sam Buchanan said:

You can remove the drain valve and clean/repair it without draining the tank. Have a spare drain valve handy (or a 1/8" NPT pipe plug) while standing next to the leading edge of the wing. Loosen the drain valve to the point where it is about to fall out then quickly pull it free, hold a finger over the hole, then quickly remove the finger and insert the plug. Very little fuel (3-4 ounces?) will be lost. Don't do this while lying under the wing unless you want an armpit full of fuel....

Most likely there is a very small piece of trash trapped under the drain valve o-ring.

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Tape over your fuel cap and vent and you will lose even less........