Piston and cylinder wear is probably the main reason. This is
what I was told at a machine shop. The wear causes fuel efficiency
to go down but you wont feel the loss of power because you will
depress the pedal more to make it up. My 84 with 150k miles runs
great. I do not feel any reduced power from the engine but the
gas mileage is down from 22 (20 years ago) to 19 MPH (now).

David

--- On Thu, 2/26/09, Matthew Snook <matt@SNOOKSBAND.COM> wrote:

> From: Matthew Snook <matt@SNOOKSBAND.COM>
> Subject: Re: Reduced Mileage
> To: vanagon@GERRY.VANAGON.COM
> Date: Thursday, February 26, 2009, 2:23 PM
> How often should we go through all that stuff?  My mileage
> was right around
> 20 as long as I drove conservatively.  Now my best is 18.5
> average, probably
> for the last 2000 miles.  Last tuneup was a year ago, I
> don't know if Mike
> put in an O2 sensor at that time.
>
> Matt
>
>
> -----Original Message-----
> From: Greg Potts
> Subject: Re: Reduced Mileage
>
> ... I know my fuel economy is down since the summer time
> but I figure I also
> have other  contributing factors to blame as I haven't
> replaced any of the
> ignition components or the O2 sensor since I got the van
> last April...