Anybody experiment with tire pressures and mpg?

[Sheldon]

I've been getting pretty bad mileage lately -- first full winter with my
"new" '97 Outback -- and noticed a drop in the mileage (below 20 mpg). I
checked the tire pressures and they had dropped about two lbs., I assume
because of the lower temps, so I increased it and we'll see what happens. I
usually run 30 lbs all the way around.

My mechanic noticed gas in the oil on my last change and attributes it to
short trips. Said I should change it at least every three months regardless
of mileage. The car uses virtually no oil.

Any thoughts on either of these? I can't think of what would get gas into
the oil, and the car runs well and has plenty of power.

Sheldon

 

[isquat]

I've been getting pretty bad mileage lately -- first full winter with my
"new" '97 Outback -- and noticed a drop in the mileage (below 20 mpg). I
checked the tire pressures and they had dropped about two lbs., I assume
because of the lower temps, so I increased it and we'll see what happens. I
usually run 30 lbs all the way around.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=3

 

[Yousuf Khan]

I've been getting pretty bad mileage lately -- first full winter with my
"new" '97 Outback -- and noticed a drop in the mileage (below 20 mpg). I
checked the tire pressures and they had dropped about two lbs., I assume
because of the lower temps, so I increased it and we'll see what happens. I
usually run 30 lbs all the way around.

My mechanic noticed gas in the oil on my last change and attributes it to
short trips. Said I should change it at least every three months regardless
of mileage. The car uses virtually no oil.

Any thoughts on either of these? I can't think of what would get gas into
the oil, and the car runs well and has plenty of power.

Sheldon

I tend to run my tires at 36psi nowadays. However, I've only noticed at
best a 1 mpg improvement (if that). I tend to prefer the higher pressure
because the tire wears more evenly. Most cars these days have
underinflated tires, even by design from the manufacturer.

Yousuf Khan

 

[Steve Parker]

Sheldon,
I would say that it is cold transmission and differential oil partly to
blame. That is full time 4wd system and the oil in these systems gets
very thick at cold temps. Also the engine does not reach operating temp.
as quickly and a cold engine is less efficient. I would suggest a change
to all synthetic oils in all systems. This will increase fuel economy
and make it easier to start when cold.
Sparky

 

[Rick Courtright]

I've been getting pretty bad mileage lately -- first full winter with > my "new" '97 Outback

Hi,

Lots of thoughts... none of them will hit the nail on the head but may
add up to a partial answer.

Tire pressure: yes, I've played with it over decades and different
"generations" of tires. My personal experience is I've settled on
generally running my tires about 2 psi over the door sticker for most
purposes. It helps fuel economy a LITTLE, but increased tire mileage and
handling qualities are the real benefit.

Cold: I don't like cold and don't get moving well when it's cold. My
cars are just like me! I don't know how cold your winter weather is, but
you may benefit from using the lightest weight fluids recommended in
several systems: engine oil, transmission and differential fluids.
Whatever applies. If you're already at the lightest weights, synthetics
SOMETIMES help cold parts move better, quicker than dinos of the same
weight.

Fuel: many areas use "winter blend" fuels that are more volatile blends
to start and run easier at low temps. Unfortunately, that extra
volatility usually causes them to turn in worse, to MUCH worse, fuel
economy. This is especially true if your trips are short or involve a
lot of idling. My freeway driving in cooler temps shows little mileage
change, but my "round town" driving shows big drops.

Gas in the oil: yes, this is a common problem w/ cold engines and short
trips. Though it was probably a bigger problem in the days of carbs, it
can still happen w/ injected systems. What happens is you run a richer
mixture when it's cold, especially at startup, and some of that extra
fuel in the mix can migrate past the rings into the oil. This happens
all the time. But in warmer weather, or longer trips, the engine warms
the oil enough to evaporate the fuel and it's pulled thru the PCV system
and burned off so we never notice it. If your running conditions don't
allow a good warmup, then liquid fuel CAN build up in the oil. That's
one of the reasons you almost always see "the book" recommending an oil
change at "x miles, or every y months." Your mechanic wasn't telling you
a story.

Another angle would be to make sure all the usual "maintenance" items
like air and fuel filters, plugs, wires, etc. are in good shape. A check
of any stored codes, looking for things like weak O2 and other
temp-related sensors might reveal something that needs attention, too.

As I said, none of these things is THE answer, but all play their parts.
There's good news, though: Spring's coming!

Rick

 

[Edward Hayes]

+1 for Rick who covered it all. I will add one thing. Don't let the
engine idle more than one minute before driving off. Your car will
warm up quicker and use less fuel as a cold idle will be running a
richer mixture longer and you're getting 0.0 mpg. Ed

 

[KLS]

+1 for Rick who covered it all. I will add one thing. Don't let the
engine idle more than one minute before driving off. Your car will
warm up quicker and use less fuel as a cold idle will be running a
richer mixture longer and you're getting 0.0 mpg.

Yes, but also, when you drive off, don't be flooring the accelerator.
Try to drive gently for the first mile or so, keeping RPMs under
3,000.

 

[Sheldon]

I tend to run my tires at 36psi nowadays. However, I've only noticed at
best a 1 mpg improvement (if that). I tend to prefer the higher pressure
because the tire wears more evenly. Most cars these days have
underinflated tires, even by design from the manufacturer.

Yousuf Khan

I normally use a tire tread depth gauge to check tire wear -- and adjust
pressures accordingly.

 

[Sheldon]

Yes, but also, when you drive off, don't be flooring the accelerator.
Try to drive gently for the first mile or so, keeping RPMs under
3,000.

Thanks, all. Good answers.

 

[Yousuf Khan]

I normally use a tire tread depth gauge to check tire wear -- and adjust
pressures accordingly.

Yeah, I don't have a depth gauge, I just eyeball it.

Yousuf Khan

 

[Yousuf Khan]

Yes, but also, when you drive off, don't be flooring the accelerator.
Try to drive gently for the first mile or so, keeping RPMs under
3,000.

Keeping under 3000 RPM? That's usually the maximum RPM that I'll shift
at.

Yousuf Khan

 

[Rick Courtright]

Keeping under 3000 RPM? That's usually the maximum RPM that I'll shift
at.

Hi,

LOL... guess I grew up in another era!

When I was learning to drive, British 4 cylinders were still pretty big
in the US, along w/ other European makes. The Japanese were barely here
and the engines they brought were similar to the British. VW Bugs (real
ones) were pretty big. Most people I knew thought a 2 liter was a BIG
four.

The rule I was taught: "If you're going to drive a 4 cylinder under 3000
rpm, turn the ignition to 'off'."

I guess it stuck... except when the engine's cold, I still downshift if
it looks like I'm headed below 3 grand!

Now a six is different, an eight way different...

Rick

 

[KLS]

The rule I was taught: "If you're going to drive a 4 cylinder under 3000
rpm, turn the ignition to 'off'."

I guess it stuck... except when the engine's cold, I still downshift if
it looks like I'm headed below 3 grand!

Same here: I shift typically at 3,000 or 3,500 rpm. Too many people
shift too early, and the poor engines lug. The 4-cyl Subaru is fine
with this and is pretty peppy; the 6-cyl Audi really likes it and
prefers being shifted at 4,000 rpm and is very easily downshifted.

 

[Body Roll]

Same here: I shift typically at 3,000 or 3,500 rpm. Too many people
shift too early, and the poor engines lug.

This won't have anything to do with the dental equipment like sound
emanating from
the subaru exhaust, would it? I won't mind to keep it up but the
toothache soon
sets in. I'm slowly buying into that american thing of the "proper
exhaust note".
Previously I thought it's the rice thing, but now I think the dental
drill sound
of the engine on my OBS brings out the worst in me. Maybe a moderately
loud fart
can can drown that a bit. Never needed one before and hope to never
need
one in the future.

 

[KLS]

This won't have anything to do with the dental equipment like sound
emanating from
the subaru exhaust, would it? I won't mind to keep it up but the
toothache soon
sets in. I'm slowly buying into that american thing of the "proper
exhaust note".

Well, I'm sympathetic here: the Subaru does whine more than the Audi,
but I should also disclose that I drive with my hearing aids off, so
perhaps I tolerate (or just don't hear! imagine that!) the auditory
experiences you unfortunately enjoy. Maybe try an Audi A4?

 

[Sheldon]

Same here: I shift typically at 3,000 or 3,500 rpm. Too many people
shift too early, and the poor engines lug. The 4-cyl Subaru is fine
with this and is pretty peppy; the 6-cyl Audi really likes it and
prefers being shifted at 4,000 rpm and is very easily downshifted.

Depends so much on the engine. I had a TR-6 that would pull like a train
from low revs, and if you ride a Harley you don't even have to shift coming
into and out of a turn. Torque rules, but you can't seem to get much from a
4 cylinder engine. Then again, sometimes it's nice to rev out a 10 or 12
cylinder engine just for the sweet sound. And if you buy a Ferrari, half
the price of the car is the music that comes out of the tail pipe(s).

 

[burdock]

I have a 1996 Outback with the 2.5 and has any body tried running in
only 2 wheel drive and do you know how to do it lots of us around her
do it in the summer for better fuel mialage