RE: AC vs MPG

[Larry Smeins <lsmeins@ball.com>]

As a comparison:  87 5KCST, 5 speed manual.

I get 27 to 28 MPG without air commuting 40 miles each way with 1/2 of
that on intertate running 75 to 80 and 1/2 on two lane running 60 to 65.
With air this drops to 25 to 25.5.  For my turbo, with knock sensor and
computer controlled timing, I find fuel octane very significant on fuel
mileage.  In Colorado the grades available are 85, 87 and 89 octane.  I
find nearly 2 mpg difference between 85 and 87 and 1 mpg between 87 and
89, with 87 being the best.  I found this by mixing fuels and measuring
mpg back before three grades were available.  I found a definite peak
with a 50/50 mix of 85 and 89.  Can't tell any difference in performance
between 87 and 89 but 85 really cuts power back.

Before replacing the AC clutch tighten or replace the belt.  A squawk
from a loose  belt isn't unusual when you try to spin the compressor up.
Try the cheap things first. 


	>Date: Wed, 6 Aug 1997 17:20:21 -0500
	>From: Phil and Judy Rose <pjrose@servtech.com>
	>Subject: AC vs MPG

	>Now that my trip computer is functioning, I hardly have time to
focus my
	>eyes on the road ahead ;-)

	>One of the things the computer seems to be telling me is that
the AC >takes
	>a pretty big (bigger than I expected) bite out of the fuel
economy.  For
	>example, when cruise-controlling on a level stretch I engage
the AC and
	>immediately see the instantaneous MPG drop by about 3
miles/gal! Isn't >this
	>a bit too much? I'd expect 1 or two at most, but don't really
know the
	>typical cost. My AC clutch seems in need of repair as indicated
by the
	>occasional squawking it does. I wonder if there's (that much)
extra drag
	>from a bad AC clutch?

	>As a side issue: With the AC off ( windows closed) at 70-75 mph
on >gently
	>rolling, but basically level expressway terrain--my '89 100
(automatic) is
	>getting a little under 24 mpg. This is based on the computer
and a fill-up
	>after a couple of 150 mile trips. Is it reasonable to expect
much better?

	>Phil
	>'89 100

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>   >       *  Phil & Judy Rose     E-mail:              *
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