Me and my friend went to pick n pull today. We took his car though and he was able to pull 40mpg out of a 2006 chevy cobalt. Now he did some of this by shifting the auto trans into neutral as we were going down hill. I think this will work for my jeep but is that good for the engine or transmission? The only thing that really worries me is switching it back in gear.

 

i don't think it's a good idea. i was taught that the vehicle should always be engaged with the engine while moving, and it's not like it's doing all that much work going downhill with an automatic transmission anyway

 

The trans slows the engine down. And I know it's okay when you down shift the engine to 3 or 1-2 while in drive.

 

http://www.popularmechanics.com/cars...l-fuel-economy

 

from my knowledge I have driven cars with Air/Fuel Gauges...although your thoughts makes sense it is really not too true. When you are driving and have your foot on the accelerator (even the smallest amount) you are using fuel and air resulting in appx 14.7 AFR (air fuel ratio) that is average and a good AFR for cruising. when you let off of the gas but still in drive, your AFR will (or is supposed to) run to full lean AKA very low fuel. If you were to put the car in neutral which as far as the car is concerned even though you are moving, the car is technically idling, the AFR will be at its idle point which is appx 14.7. so you would end up using more fuel. if you put it in neutral. This is just my .02 and I could be wrong. Hope that makes some sense.

 

Great source and it makes a lot of sense. So in reality my friend was probably getting around 22mpg