I get good mileage

I drive this car (not the 18.T, but the “little” VR6 (as opposed to the 24-valve VR6 that came out mid-2002)), which is rated 24 city/28 freeway (not that great for such a small car).  However, my mpg (as reported by the trip computer) is currently 29.9 (over the last 300+ miles, as I near the end of another tank of gas).  When I drive home (downhill), I expect to break 30.0, as usual.  How do I do it?  Coasting.

While messing with the trip computer, which shows instantaenous fuel economy, as well as per-trip and long-term average mpg (so if you pay attention you can get a feel for how they affect each other), one day I had an epiphany: coasting (idling) at 60 mph, I can get 200 mpg!  (If I had a hybrid, I could do even better, because the gas engine would actually shut off while I coasted).  Any higher than that, my trip computer just reports 199.  And if I mix in enough 200mpg with my regular driving, I can seriously boost my mileage!

I also read an article once, testing whether some little Honda could drive from LA to San Francisco on a single tank of gas, which  mentioned that “competitive” mileage drivers rev up through the maximum torque band (when the engine delivers the most acceleration per drop of gas), and then coast back down to a stop.

Obviously, that kind of driving is not feasible in the presence of any other drivers, but I have managed to reach a compromise that netted me measurable savings in gas costs, without risking death by road rage.  Here are my basic rules of thumb:

  • Always coast down hills
  • Going up hills, and in slow traffic, maintain a constant speed, and enough distance to the car in front that you don’t have to constantly brake and accelerate.
  • On the flat, gently but firmly (not foot-on-the-floor) accelerate up to 85 (which is only a hair above the average speed of traffic in San Diego) and coast down to 60 (I would guess on the flat I would generally accelerate for less than 10 seconds, and coast for about 30)
  • Try to stay in a traffic bubble, so you have plenty of room to coast way back to the car behind.  It helps to get in front of a slow truck.
  • Try never to brake.  Learn to gauge exactly when to let off the gas — if you have to brake, you were on the gas too long; if you don’t touch the bumper in front of you then you could have accelerated more (and subsequently coasted more) (that’s an exaggeration, of course)
  • If somebody comes up behind you who isn’t easily able to change lanes around you, break the coast early; think of how you would feel when you’re in a hurry, and the idiot in front of you is not only going 65, but slowing down!

Of course, this whole concept only works if you drive a stick.  If you drive an automatic, well, you’re not really driving, are you?

2 Responses

  1. Part of this is the manual implementation of the automatice gas saving technique of my ’63 Saab that I had a long time ago. Its approach was to automatically sever the drive shaft from the engine whenever the driver let his foot off the gas. You would we coasting, then, and the engine would be idling.

    So, your ‘coast down hills’ rule – does it include shifting to neutral?

  2. Absolutely. I have found that, although mileage goes up if you coast in gear, the “engine brake” action slows the car down a lot faster than just coasting. I’m not for sure, but I think that coasting in gear nets less gas savings. In any case, I prefer longer coasting, for less lurchiness overall. I just hope I’m not toasting my clutch. I think I’m probably using the clutch equivalent to city driving all the time.

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