[hharney]

I agree with Ed, do it by the book. I take off and climb to cruise altitude and after about 1 hour on the main tanks, I select both aux tanks. I start my 1 hour timer and after 1 hour I switch the front back to main and leave the rear on the aux. When the rear coughs I switch the rear back to the main and then switch the front back to the aux. When the front coughs I switch the front back to the main. Usually total time on the aux's is 1.25 to 1.3 hours. I watch my clock, fuel gauge and fuel flow for indications. Once in a while the cough will catch me by surprise.

Depending on terrain or location I will stay on mains longer than 1 hour. But for the most it's right around an hour like the book says.

Once the aux's are drained you know that all the fuel you have is in the main tanks. I calculate the time very conservatively and figure my reserve. I know my fuel gauges even though lots of people and pilots in the right seat point and question them. Mine are only trustworthy when they are 1/4 or lower. For the most part they work pretty good and after flying this airplane for 35 years you get to know the systems.

I know have a JPI with fuel flow and I am starting to learn to use it as a tool also. It is amazingly accurate. I have it tied into the Garmin 530 and it continues to amaze me with it's right on numbers.

At times I will put 10 gallons in each aux just to have some fuel sloshing around in the tanks and I have used that hour or so of fuel in some cases but never because the mains were too low. I almost always top the mains after each flight but only use the aux's for cross country flights. I almost never let the mains below 1/2.