James wrote:
> 1.  Can anyone offer suggestions as to why my transfers are beginning
> at lower values suddenly?
> 2.  Does anyone have any thoughts as to how I could transfer fuel
> overboard, even though my header read at max 8 gallons?
> (Later, on the ground, I pumped the header up to 12 gallons without
> venting any fuel overboard.)

James:
First, I'm guessing that you have optical or float-switch level
sensors inside the header tank to activate the automatic pumping.
Both high and low switches would have had to failed to explain
both the low level at pump start and the low level at pump stop.

I've always considered the sight tube to be the most reliable
fuel level indicator. However, the simplest explanation for your
observations is a failure of the sight tube indicator. If the sight
tube were clogged at the top somehow, then trapped air in the sight
tube would have no place to go as fuel is added to the tank.
The electronic switches activating the pump may have been functioning
normally. Manually pumping fuel to the header would cause the indicated
fuel level to rise somewhat, but once the tank is full it would pump
fuel overboard.

In my aircraft, I can smell the fuel once it starts exiting through the
vent tube. Presumably that is due to the poor canopy seal, and air
sucking in through the small drain holes in the floor.

-bob