Date: Sun, 17 May 1998 22:41:38 -0500
Reply-To: Steven Broomhead <broom-sr@SWBELL.NET>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Steven Broomhead <broom-sr@SWBELL.NET>
Subject: Re: FS diesel engine
Content-Type: text/plain; charset=us-ascii
Forget it!!!!!!!!!!!!!!!!!!!!11
I'll let the junk man have the engine for free.
I think I will retreat back to a lurcker .
Joel Walker wrote:
> On Sun, 17 May 1998 20:25:35 -0500 Steven Broomhead said:
> >If my tanks holds 10 gallons, say I let it idle in my driveway for 3 hours
> >and then start the trip. My tank would run dry at 225 miles. My true mpg
> >would be 22.5, BUT I used x (unknown qty of fuel) during the 3 hour idle.
> >Since the engine does not idle on pure air, the amount of fuel used is
> >negligable.
>
> in theory. but in test on my 86 van, with a trip computer installed (that
> measured the amount of fuel used, and was pretty darned accurate ... down
> to 0.1 gallon), i found that that particular van used 0.6 gallons per hour
> idling in the driveway. yeah, i know ... who'd REALLY be dumb enough to
> do this. well ... it SEEMED like a good idea at the time. :) but i was
> fooling around with the trip computer and the new bus, my first water-cooled,
> so i wanted to see what it would get. what i found was this:
> Bentley says: 18 mph per 1000 rpm.
> 1986 data: 16.4 mph per 1000 rpm. tires, friction losses, and air drag,
> i guess.
>
> so i had a table like this:
> calc range in
> rpm mph gph mpg miles*
> 3000 49.1 - - -
> 3200 52.3 2.3 23.1 346
> 3400 55.6 2.4 23.6 354
> 3600 58.9 2.7 21.2 318
> 3800 62.1 3.2 19.2 288
> 4000 65.4 3.3 19.8 297
> 4200 68.7 3.7 18.8 282
> 4400** 71.9 4.3 16.8 252
>
> - = no data. people were trying to run me off the road at that speed. i also
> couldn't get up the very small hills on my "test track" of a pretty flat
> area on the interstate highway just west of here.
> * = assuming you ran 15 of the 16 gallons in your tank at this speed.
> ** = only got to run one short test at this speed, so i didn't have enough
> data to average (like the other speeds: they were all averages of three
> test runs). remember, this was back when 55 mph was the interstate
> speed limit. and a bus makes a very good radar target!! :)
>
> now, in real-world driving, you can't just sit there on cruise control all
> the time. people slow down in front of you, you can't pull out when you need
> to get around them, you have to stop for red lights and all sorts of things.
> dirty bus = higher drag. tires get low on air = higher drag. that sort of
> stuff. so what i found was ...
> - best speed for best mpg: 3600-3800 rpm. below 3600 got better mpg, but
> didn't have enough omph to get up
> most hills. and hills REALLY dragged
> the mpg down (the trip computer would
> also show instantaneous mpg).
> - worst speed for mpg: above 4000 rpm. the higher rpm you drove, the
> worse the mpg got.
> - best ever mpg: 24.3 mpg.
> - worst ever mpg: 14.9 mpg.
>
> >In short, no matter what my driving habits over the course of a year my mpg
> >averaged 25 MPG +/- 1 MPG.
>
> then i would suspect that
> - you drive slower than most folks on the road.
> - you drive mostly highway miles
> - you keep your tires pumped up
> - you keep your bus clean and shiney.
>
> ... or you're not keeping the records right. on mine, i had to make sure that
> i filled up the tank to the same spot in the filler neck. otherwise, there
> could be as much as a half gallon or more difference in the amount used to
> fill up. plus the time of day makes a difference ... fill up at night and
> you get a little colder gasoline, which is more dense, so you can cram a
> little bit more into your tank. fill up at 2.pm in the afternoon, and the
> gas is pretty warm and expands to fill the tank with less gallons. now,
> with the small 16-gallon tanks we have, it's not gonna be a whole lot...
> maybe not even noticeable, like a few ounces. but all these factors can work
> against you ... and if you depend on the pump nozzle kick-off (when it stops
> pumping), you can also vary quite a bit ... not all pumps are the same.
>
> my point being that even if you do it super-critcally, you can STILL come up
> with differences. the reason i did three runs at each rpm and averaged them
> was because at different times of the day, in different weather, i'd get
> different results. oh, they were close, but not exact.
>
> joel
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