Speed to get highest mpg?

[McPatrick]

I'm sure this question has come by here before but I have searched for it and couldn't find it so here it goes: going down from say 70 mph will get your FE up. But suppose I just put the last available gas on earth in my tank and I would want to drive as far as I could with that last gas tank how fast would I have to go? Is 10 mph better than 40 mph? or is it the lowest speed in which you can drive in 5th gear?
(Oh and I am also assuming the roads would not be full with cars that wouldn't be able to drive any further ).

[mpg_maniac]

I've seen people here say that P&G (Pulse and Glide) would get much better MPG than using a constant speed. I've been testing it out on straight aways as much as possible lately to see how much difference it makes.
I've been slowly going from 60 and gliding to 40 then speeding back up to 60 again.

[ELF]

For most cars with a auto tranny a constant speed at around 35-40 mph will deliver best mpg.
Manual tranny is probably different.

[lca13]

one guideline I heard that made sense was the the best fuel economy generally comes in the highest gear at the lowest rpm.... not so low that you are luggung or anything but the lowest comfortable steady state load.

[omgwtfbyobbq]

Originally Posted by McPatrick

But suppose I just put the last available gas on earth in my tank and I would want to drive as far as I could with that last gas tank how fast would I have to go? Is 10 mph better than 40 mph? or is it the lowest speed in which you can drive in 5th gear?

You would go about as fast as this. In Metro's case, it comes to a ~133mpg@22mph average. Which is pretty much optimum. Some guys did ~160mpg@17mph iirc in an Insight. I've also seen this same driving style referred to in older articles about how to get to that next station if you're nearly dry.

[GasSavers_Ryland]

the book How To Get More Miles Per Gallon says that in an emergency you can get up to 100 miles per gallon by slowly speeding up to 20mph and killing the engine untill you are going 5-8mph and restarting and gettting back up to 20mph, repeat, of course this book was written in 1978, so that 100 mpg was with a big heavy carburated car, and was only advocated for use in an emergency.

[JanGeo]

I get 60mpg indicated at 20mph on level road in 5th. Mileage drops to about 50mpg at 30mph. The problem with going too slow is lubrication in the engine is not as good for long term operation (more than 10-15 minutes) and that may affect mileage eventually.

[Hockey4mnhs]

i wish i had a scangauge!!!!!!!! its so much easyer!!

[cfg83]

JanGeo -

Originally Posted by JanGeo

I get 60mpg indicated at 20mph on level road in 5th. Mileage drops to about 50mpg at 30mph. The problem with going too slow is lubrication in the engine is not as good for long term operation (more than 10-15 minutes) and that may affect mileage eventually.

Yeah, I see around 50 MPG between 30 and 40 MPH in 5th in my Saturn. I should make a chart to see where the aero-drag begins to hurt me.

I wish we had "normal speed" parkways in LA. I wish I could find my urban planning notes, but I think that super wide streets like Venice and Hawthorne were originally designed with this in mind.

Rosemead/Lakewood Blvd is interesting in this respect. In most places, the road dips down to allow a train bridge to cross over it. The train stays flat so that it doesn't have to waste energy going uphill over a bridge, but the cars don't have to wait at a train stop.

CarloSW2

[96hb]

In my Civic I have been cruising around 55-60mph on the interstate and doing the speed limit everywhere else and getting 47-50mpg respectively. I suppose if I drove slower it might be better, but I just can't do it! And I think that 50mpg in an 11 year old Honda is pretty darn good!