Thread: question on mileage

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Question I've wanted to ask for many years. On either a engine with carbs of Fi, the story about saving fuel is less RPM's less gas used. Now lets take a 5 speed manual tranny. Going down the road at 60 with rear gears of 3:00(just an example) your turning around 3200 RPM's. You shift to 5th gear and your RPMS drop susposely to save gas. What happens when you come to a hill and you notice in that gear that you loosing speed and you give it more gas. Now my question is if you don't downshift to 4th gear, your going to be using more gas trying to get up the hill in 5th. Right or wrong. Always open to commemts.

Today it seems that everyone wants to get up to that lite while its RED so they can check there texts on there phones

Chevy 37, Dennys wisdom is correct and his advice always seems to be spot on, Streetrodder or Rod & Custom had a write in article on a similar question years ago, keep in mind a performance camshaft raises the power band of a motor, a stock camshaft is desgined to produce power and mileage at 2100 as an example, a new "hotter" cam raises that to possibly 2800 or maybe even higher so the power band at 2100 is going to make you stab the loud pedal going up that hill. So I guess what the article said in a nutshell is it depends on the vehicle and the motor in it.
I knew a guy who had a V8 trike and thought his gas mileage was terrible and with a 350 turbo in 3rd gear was turning 2400 rpm's or so at cruise speed, he installed a 700 R4 and dropped cruising speed down to 1800 at the same speed and his fuel economy got way worse, noy to mention even if it did improve he never would have saved enough to pay for the $1800 change in transmissions anyway, kinda like spending 40k for a Chevy volt to save gas money???

Denny and Mattyj, thanks for the replys. I understand all what your saying. I drive 200 miles /day 6 days a week with a 2o10 Nissan frontier with a 6 cylinder engine. On the freeways afer I hit 60 I changed gears to my 5th. At 70, I changed to my 6th. For comparison, I drove the distances in 4 th gear all the way with my tack around 3700 RPM. The next time I used 5th gear. Now taking into consideration the weater(hot or cold) I got better mileage in 4th around 20.5/mile. In 5th gear I average 19.8. In 6th gear having to downshift alot, The mileage dropped to 18. Just seemed a bit odd, but your both are right.

I suppose you could sit down and crunch some numbers to figure out less throttle in lower gear vs. more throttle in higher gear but it would be theory anyway. The real gas saver is the right foot and its associated pedal.

If you're really worried about it, drop some speed going up the hill, and switch the AC off. Then on the back side of the hill, recoup your speed and switch the AC back on. Down shifting is a judgement call, use whichever gear lets you press lighter on the pedal.

Originally Posted by firebird77clone

Down shifting is a judgement call, use whichever gear lets you press lighter on the pedal.

And this is why all the new cars are all automatic / computer controlled with 6 to 10 speed trannies.

I recall reading an article written by one of the top mpg driver's back in the days when they did measured distance challenges (was it the 60's??). His key was to accelerate crisply up to cruising speed, and then drive as if there were a raw egg under your throttle pedal.

Don't just watch the lite coming up-look further down the road to the 2nd or 3 rd visable lite------get used to how long they are red/green------don't gas it hard to get thru as it changes---------if lite has been green quite a while you can back off a little early to coast further plus you'll be at the front of line for choices at the next segment-------

In aviation there is a speed rate known as "best rate of climb", or the speed that will get you the altitude your climbing to(CRUIZE) in the least amount of time-everybody knows that cruise power is more effient than climb power----------BUT----at a higher speed during climb will take you longer to get to that more effient speed--------you get a lot further down the route with less fuel used and in less time IF you climb at a higher rate of speed--------

Getting to that most effient speed sooner helps, but in the long run your brake wear will be one of the better indicators of your driving efficienty-----

On my daily driver I try to shift at 2k in every gear and I run at 68-70mph. The truck will get 21-22mpg all the time that way. If you lug it or rev it out to near 3k each shift, it'll drop down to around 18mpg. Not really apples to apples since mine is a diesel and yours gas, but same rules apply. Try to keep the rpm's down while accelerating, and try not to let the engine get over loaded in the wrong gear etc.

With two Dodge Rams, both 318's, one auto one 5-speed stick, I checked mileage for two tanks of gas each, using OD normally. Then I didn't use OD for a couple of tanks, driving as much the same as possible. Guess what? Not a bit of difference in mileage. Nada! None! Mostly country driving, 60-70 MPH cruising. OD reduces wear and tear and like that, but not much gas savings. Same thing with my '54 Bel Aire, with a '55 4.11 rear and OD three speed. It actually got worse mileage in OD, like 3-4 MPG less. But my '88 LTD 302 did get better in OD, so sometimes it works, I guess.

My 01 Silverado, auto, OD. may need an adjustment somewhere, but I think it's a programming issue. Anyway, it goes into OD too soon and doesn't downshift for hills so I'll do it manually. Part of the issue might also be the nut behind the wheel. The computer decides to downshift based partly on how much pedal is applied, and if I don't increase pedal on the uphill then the computer doesn't know it's on the uphill.
As for going into OD too soon, and this is just my viewpoint, I don't think it has any business in OD under 55 unless I'm going down hill.

A computer is only as good as its program.

Originally Posted by firebird77clone

....A computer is only as good as its program.

I agree, but I'd add that the computer is only as good as it's inputs. What you describe sounds like a weak vacuum modulator, or perhaps a vacuum leak. My impression is that your tranny computer will sense the hill by changing vacuum, which it detects as load, whether you move the throttle or not. You might consider a visit to a good, independent tranny shop for a quick diagnostic check.

Chevy 37, sounds to me like for your 6 cylinder drive your two OD gears are more for reduced wear & tear than improved mileage. If you've put taller tires on you've dropped your rpm range at any given speed, and that can affect MPG a lot. Jeeps have a power band sweet spot that's about 2100 to 2500 rpm's, and throwing on a set of 33's can drop you out of that if your rear gears are not tall enough. You could probably play with the rear gear ratio and tire OD to fine tune some, but the savings in fuel cost won't pay for the changes, I expect.

Originally Posted by 34_40

And this is why all the new cars are all automatic / computer controlled with 6 to 10 speed trannies.

I drive a lot (50K+ a Year), and I like GMC pickups (specifically, white Z71 SLT Crew Cab ones)-

So, I go through one about every 3-4 Years or so (it ain't cheap)-they are all equipped with 5.3's. 3.42 rear axle, posi, Tow pkg., etc.)-

Anyway, the reason I am telling you this is that I have always got around 21-22 mpg (on the highway) with this combination (I live in the western US, and drive the in the Mountains almost exclusively)-

So, when I got my first 2011 pickup, it took me awhile to get used to the 6 speed Transmission-after break-in, the first thing I noticed was that my Gas mileage dropped down to about 15-16 mpg (highway)-I surmise that our western rolling hills and mountains are making the Trans shift a lot more, and it will stay in, say 5th going up a hill (so it uses more Gas-when it is hilly it seems to be constantly shifting)-

The upside? These newer Trucks (with the same Equipment) will absolutely stomp my old body style, 4 speed truck-bad-(I've talked my way out of 2 Speeding Tickets in just the past Year-remember, always be nice to the Officer!)-

Originally Posted by 35WINDOW

I drive a lot (50K+ a Year), and I like GMC pickups (specifically, white Z71 SLT Crew Cab ones)-
So, I go through one about every 3-4 Years or so (it ain't cheap)-they are all equipped with 5.3's. 3.42 rear axle, posi, Tow pkg., etc.)-
-(I've talked my way out of 2 Speeding Tickets in just the past Year-remember, always be nice to the Officer!)-

I "use up" vehicles about every 5 years. 35 + K a year. The current DD is a Focus, 4 cyl / 6 speed auto, etc. etc.. I drive mostly "secondary roads", the car is advertised in the 39 or 40 range. I just leave it alone unless we're going down hills - then I kick it into neutral and coast, also will shut the motor off if I'm at certain known lengthy stop lights.. I can push up into the 43 to 45 mpg range if I'm lucky to an extant.

I don't do all this as a for anything more than just the challenge of it all. I get bored just driving along.. things like this keep it interesting. ANd I know 1 thing, Setting at a light will suck the life out of your miles per gallon. And that right foot deep into the little pedal on the right is twice as bad!

Originally Posted by 35WINDOW

....Anyway, the reason I am telling you this is that I have always got around 21-22 mpg (on the highway) with this combination (I live in the western US, and drive the in the Mountains almost exclusively)-

So, when I got my first 2011 pickup, it took me awhile to get used to the 6 speed Transmission-after break-in, the first thing I noticed was that my Gas mileage dropped down to about 15-16 mpg (highway)-I surmise that our western rolling hills and mountains are making the Trans shift a lot more, and it will stay in, say 5th going up a hill (so it uses more Gas-when it is hilly it seems to be constantly shifting). The upside? These newer Trucks (with the same Equipment) will absolutely stomp my old body style, 4 speed truck-bad-(I've talked my way out of 2 Speeding Tickets in just the past Year-remember, always be nice to the Officer!)-

So are you saying that in your older model trucks (Pre 2011) that had the 4spd auto you'd get 21-22mpg, but the newer style seems to always be shifting, and only knocks down 15-16mpg but has lots more highway power? No big deal, just wanting to understand your experience.