Fuel Rate at Idle Question
 

I have a new UltraGauge and have been using it on my 2002 Jeep Liberty (4wd Limited Automatic) and on my 2006 Honda Odyssey (EX-L Automatic). I have noticed in the Liberty, if I sit at a light at idle it will consume measurably less fuel if i put it in Neutral versus in Drive. (~0.5 GPH in Drive vs ~0.4 GPH in Neutral) When I try the same thing on the Odyssey, there is no measurable difference. In the Liberty I don't have the AC on, but the Odyssey usually does have it on since the climate control is always on for my wife and kids. Could this be the reason or is there something else going on? On the Odyssey, the fuel consumption rate is a bit more "noisy" than on the Liberty, i.e. the reading jumps around a bit more.

Can anyone with more insight explain the difference between these two automatics?

Depends a lot on the torque converter and trans pump. My intrepid goes between .450 when fully warm and. 550 if not warm. Will drop a little if I go to neutral, almost no change once at temp.

I do see a change in my Odyssey between D and N. However, as you observed, having the AC on dwarfs that change. Try running the air on Auto-AC Off for a bit next time. Also, the Auto ac system is smart and cycles the compressor on and off only as needed - if it's cycling you'll see jumps in fuel consumption to match.

That would suggest not but some cars already shift to neutral at idle without any change in the position of the selector.