Down On The Urban Farm

I've been reading some of the hypermiling forms and blogs lately and have been paying more attention to my driving habits in an effort to see what kind of mileage I can get without going to extremes.

I have one of those new 2008 V6 HOnda Accords that shuts down three cylinders under light loads. I can get almost 27mpg in mostly city driving just by taking it easy on the accelerator and coasting up to stop lights.

SOme tactics are just not reasonable. It's 110 degrees outside in the afternon: I'm not shutting the engine off while waiting for the light to turn green. (perhaps this winter though). And with power steering and power brakes, shutting the engine down while coasting doesn't seem like a good idea.

That's what your car gets while you are sitting at the light waiting for it to turn green.

In my (much) younger years, the solution would have been to take a quick look around for the cops and then blow the light. I'm too old for that now.

I'm tryng to do what the real hypermilers do: pay more attention to what's going on ahead of me. If the light turns yellow - or is about to - I take my foot off the gas and start slowing down a lot sooner. My objective is to minimize the amount of time I spend getting zero miles per gallon.

A common practice among hypermilers is to shut off the engine when coasting downhill.

Some of the newer cars have this functionality built into the engine management computer. For my 2008 Honda Accord, HOnda says:

Fuel Cutoff Control
During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at engine speeds over 850 rpm (automatic transmission) or 1,000 rpm (manual transmission).

I guess are cars are sometimes smarter than we think they are.

There is a technique the Hypermiling gurus call Forced Auto Stop (FAS) that involves taking the car out of gear - or even shutting the engine off - when coasting downhill.

One of the interesting things about my 2008 HOnda Accord is that the onboard computer does this automatically. WHen the car is coasting downhill, the throttle is closed, and the RPM is above idle, it automatically shuts off the fuel to the injectors.

Because the Accord shuts down 3 of its six cylinders when just driving along steady-state, I find that I get slightly better fuel economy by accelerating from a stop at a normal pace than if I accelerate at a very slow pace - it allows the engine to go into three-cylinder mode sooner.

Online University has published 50 Simple Techniques that Will Increase Your Gas Mileage

In general, No.

It is a common misconception that higher-octane (premium) fuels improve gas mileage. Octane rating has nothing to do with the energy-content of the fuel. A fuel's Octane Rating is simply the measure of the fuel's resistance to auto-ignite (ignite under pressure without spark), also called 'knock' or 'predetonation'.

In other words, premium-grade fuel is actually less volatile than regular.

Some automotive engines do in fact require premium. Engines with a compression ration of 10:1 require the higher octane fuel to prevent predetonation (due to the higher pressure levels in the cylinders).