Gas mileage mystery

He wrote: "Itseems that I get about 140 iles to the first
half tank...the second half drains...I only get about 80
miles from the middle point of the gage to E..."

That is equivalent to mpg only if you assume that each half
of the gauge represents the same number of gallons.

 

He also wrote "If I fill up a half empty tank, I'm getting close (not quite)
20 mpg...if I let it get near Empty I'm looking at about 14 mpg". That is
(possibly) incorrect only if you assume it was based on the gauge. You think
he didn't even twig that "near empty" could mean another 50 miles?

 

what really surprises me is that Volvo never included a LOW LEVEL warning
light...

my 70's Fiat had that, my '86 Corolla had that... but my 760 doesn't!! My
760 ('87) also doesn't have tilt steering, while my Alfa Romeo of the same
era had tilt/telescope!! What's up with that?!?!

 

Of course Volvos have a low fuel contents light. It is part of the fuel
gauge and is a small Red or Orange dot that lights up when there are about 6
Litres of fuel left in the tank. Your 760 is just before the facelift model
which does have the steering wheel tilt as do subsequent 760s and
960/S90/V90s. The tilt lever is to the left of the wheel (UK) between the
casing and the dash knee roll. Might be to the right on USA/Canada models.

All the best, Peter.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

 

People are often surprised when they discover what has been traded for
economy, convenience, sales attractiveness or someone's idea of progress.
Just think if it was a Ford device you'd probably be better off without it.

 

If I could read minds, I'd know. My impression from reading
between the lines of his question is that he assumed that
his gas guage accurately reflects the volume of gas in the
tank. My training as a scientist is not to trust any
measuring device until I've calibrated it, unless it came
from a source I knew did a good calibration.

Sometimes, the exactness of the reading isn't vital. I know
my bathroom scale is off from the scale in my doctor's
office. But I use my bathroom scale mostly to tell me
whether I'm gaining or losing weight, so it only needs to be
consistent, not highly accurate.

 

If you wen't back as far as I do, you would remember when
the dashboard had a meter that showed how much current was
going out of or into the battery. Voltage regulators
weren't so good, and we worried about overcharging the
battery. But we didn't have an outside temperature reading.

 

Most people never bother to do the math...
If you commute 30 miles and it takes an hour (not uncommon in LA
traffic), you're averaging 30 miles per hour.
Why then, is it necessary to go 70 mph, zero mph, then 70 again for a
few minutes?
Or, go 50 mph between signals, only to sit at the next red light?
I only commute 10 miles. It takes between 20-25 minutes. I roll along at
30-35 mph while others go flying by at 45-50, only to sit at the next
signal.
Surprise, surprise, the light goes green just as I roll up to it and I
never moved my foot on the gas or touched the gas wasters (brakes.)

 

....and if you didn't flash the field on the generator when you changed
the battery, it wouldn't charge at all.

 

....can't read minds but can read between lines Sorry to be argumentive,
when I arrived at the same conclusion as Marvin (measured properly) people
assumed the fuel gauge was to blame. A lesson in how quick many are to
assume one is stupid, I give more credit for intelligence as a direct
result.

 

hehe... well, I think a safe thing would be a low level light, prevents you
from getting stranded on the highway.

Another poster suggested it comes on at 6litres... I've never been that low,
but that is QUITE low, the gauge dips way into the red and I start to sweat
there.. the light has never come on since the car was new.(where is it?
it's not a separate indicator which is obvious, unless it is backlit in the
red section, which I doubt... I can take a pic).

Oh, and Fiat 500s didn't have a fuel gauge, JUST a light ..

 

Every fuel gauge I've had a chance to check for lineraity
failed the test. Others report the same experience. It is
a reasonable and likely explanation of the original poster's
observation.

 

............

You only have to look at the arrangement to know it won't be very accurate,
it's an equally big assumption the inaccurate gauge was used to arrive at
firm mpg numbers. Since I have repeatedly varified the same behaviour in
another car, measured by the pump, for me the obvious explanation is much
less likely. Rather than dismiss it based on assumption, I am interested in
why it happens at least in some cars, because I know it does happen.

 

Well...I have done the first two fill-up calculations....and there is
nothing that dispels my belief that I get better mileage early in the
tank.

I filled up at a half tank...I got 163 miles on 9.18 gallons of gas
I then filled up at around 3/4 tank....the gage only has a hash mark at
the half tank and the red line at about an 1/8 tank...
the 1/4 tank was actually 5.25 gallons and I got 104 miles on that 5
gallons.

So, those who said the gage is not calibrated to precision are correct,
but I still seem to get better mileage with more fuel in the tank...go
figure.

Mike