Date:         Fri, 31 Mar 2006 22:26:46 -0800
Reply-To:     Robert Fisher <refisher@MCHSI.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Robert Fisher <refisher@MCHSI.COM>
Subject:      Re: MPG Question
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
              reply-type=original

Given an engine that is running according to spec and with best reasonable
efficiency and excluding driving habits, mechanical factors that could cut
down gas mileage could include a slipping transmission, binding/dragging
brakes, fuel flow restrictions, air restrictions, improper odo reading,
computer problems, 'bad' or incorrect gas, tire pressure, open windows,
excessive weight... I'm sure there are many others but there are a few with
which to start.

Here's a brief synopsis of various issues:

http://www.artsautomotive.com/Mileage.htm

Cya,
Robert
----- Original Message -----
From: "Geza Polony" <gezapolony@SBCGLOBAL.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, March 31, 2006 9:25 PM
Subject: Re: MPG Question


> One thing to take into consideration: the wide variations in mpg we're
> seeing here could very well be related to odometer variations in these 20+
> year old vehicles.  Bentley Section 90.30 tells us that, brand new,
> odometer
> tolerance is from -1% to + 3.75%, in other words, a spread of almost 5%.
> Couple that with over- or under-sized tires, and you could get variations
> of
> 20% easy.
>
> I've noticed that going taking the exact same route from our home to our
> vacation place yields different mileage readings on the odo. And I mean
> exact same route! Maybe five miles difference over the course of 400
> miles.
>
> Claims of driving X MPH for such and such a MPG may be erroneous, too. It
> turns out the speedometers have a total tolerance, new, of almost 18%!
> (Bentley 90.30) Incredibly, VW indicates that for a real 50 MPH speed,
> speedometer readings can be up to 58.7 MPH! In other words, when you think
> you're going 75, you may only be doing 65 or so--and that's with
> absolutely
> stock tires.
>
>
> What are we really measuring, then? This is all ballpark figuring, when
> you
> look at it that way. EPA must calculate MPG using measured distances,
> rather
> than odometer readings, along with carefully measured gas.
>
> I was originally asking a mechanical question. Is there something that
> typically cuts gas mileage down even though the car runs fine? What would
> that be, if so?