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A little hypermiling experiment

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Just for fun I tried a little hyper-miling experiment on my last fill up ($3.79/gallon Chevron, SoCal). Here are some of my results. I'd like to hear from you all if you've tried this.

Currently 1030 miles on the odometer. Truck is about 4 weeks old.

R/T commute is 60 miles 90% highway. Starting point was 22.5 MPG after a WE of towing a trailer. Commute includes a long climb and a long downhill in both directions.

On the flats I'm trying to push the instantaneous readout to between 22 to 60 MPG, keeping it, on average, around 40 MPG. Cresting over the hill (about a 4 mile down grade), I switch to neutral for the ride down, topping the instantaneous at 99 MPG.

Just for fun, on the way back over the hill I decided to cut the motor (turn key off), and discovered to my surprise the power-assist steering and braking were not affected. At the bottom, the motor was restarted and I continued on until arriving home. BTW, if the headlights are set to auto, and the engine off, the headlights will turn off after 30 seconds. Went to manual headlights.

So I cruised about 4 miles downhill with motor turned off completely and in neutral. After less than three days I went from 22.5 (starting) to 27 MPG average.

I'm not sure if cutting the motor has any detrimental effects on the drivetrain. Not so sure I'll make a habit of it though.

I have a little experience at this with my Ford C-Max hybrid and consistently get 43 MPG.

What do ya'll think?
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Coasting with the engine turned off can be a BIG problem with some transmissions. If the transmission fluid pump is driven from the engine side, rather than the output shaft, then there may be no lubrication for the transmission. I have no idea if our transmission is designed that way, but many older ones can suffer from this treatment. Also, consider that you have no compression breaking when you do this, though diesels don't have much to begin with. Depending upon the state that you are in, coasting can be illegal.

That said, I have hypermiled standard transmission cars to get up to 90 mpg.

It's hard to tell what these new computer controlled transmissions will do under abnormal conditions. I also have a GMC diesel with an Allison transmission. My driveway is steep downhill and I didn't want to have the truck in reverse while backing down, so I put it into neutral and coasted backwards to not have to brake so hard. Well, that threw the transmission into limp mode. After a couple of times, I now use reverse and mash on the brakes.
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