interesting thread !
beyond fulltime on a cheyenne III since 4 years i freelance on a seneca for a small german company and from the informations givene here something is odd.
first- our flightplanner gives for CYYR-BGBW a distance of 785NM .
the longest flight i ever managed nonstop with the seneca was about 650 NM and 4:30hours to land with not more than 45min fuel on board. 785NM with headwinds has to go wrong even with correct leaning- the result is no suprize .
the seneca burns ~20gal per engine/h in climb and you can squeeze her down to about 10-11 gallons/engine in cruise leaned. ( turbocharged continental TSIO360 ) trying to lean further gives no result since the manifold pressure will start to fall and so also the speed- so you will not get out more range out of her doing this . the TAS with 10-11 gal/eng will be in FL100-110 about 160kt TAS .
roberts email about cruise fuel flow is roughly realistic,but to get to 13000feet she will burn a little more than he claims. and the distance is simply to far for a seneca - since she will do not make more than 160 knots true when leaned down to 10gal/eng.
the next thing is : at 1506 he reports 29gal on board ( being in cruise) and at 1603 the engines stop. so in an hour he burned 14.5gal/engine which is not even leaned to the limit.
and he seemed to start a shallow descend and finally had to level off at low altitudes with miles still to go.
the TSIO continentals have an altitude compensating fuel injection system which increases fuel flow with lower altitude by itself without you touching the condition lever. simultany the seneca has a significant tendency to drop in TAS at low altitudes- so he should stay high as long as possible .
the last thing : making 160 TAS results in nearly 5 hours with no wind , so at altitude he did not even had a hard headwind.
it seems that nobody had experience on a seneca and they simply made a mistake what you can expect from this plane and what not.
best regards !