Most fuel efficient acceleration rate?

[chndrcks]

My 05 3.7 (almost exactly 1 year old - just hit 9000 miles) has been getting around 14-15 mpg lately. Most of my driving is city (30-40mph) with occasional short (2-3mi) trips on the interstate (55mph b/c of construction, normally 65).

Of all the tips I've read on improving gas mileage, I think the one that will help me the most is not accelerating so quickly*. My concern though is that it seems that accelerating too slowly could be just as inefficent as accelerating too quickly. Is there some sweet spot in the middle I should be aiming for? I've been trying to keep my RPMs under 2000 when accelerating, is that too low? just right?

My follow-up question is what's the ideal speed to maintain? Am I right in thinking the most efficient would be the lowest speed of the highest gear? (For example, I've noticed my liberty changes gears around 32mph, if I would normally be driving at 37, should I drop it down to 32-33? or are those kind of changes not going to make a difference)

Sorry for all the questions, I start typing and they just starting popping into my head. Any other tips are appreciated - as you can probably tell I'm a bit of a newbie (but I love my KJ).

*I try to time stoplights so I don't have to stop, but with stop signs, people turning and lights I always miss, I find myself having to accelerate a lot on the drive to work.


sorry if this should be in the gas mileage sticky - I wasn't sure the thread was for asking new questions

 

[jfortier777]

ideal fuel consumption is realized at 2k RPM.

This equates to approx. 75 mph on the highway.

Keep in mind that the shift points are lightly different for all of us because of the learning computer that controls our transmission.

Mileage decreases on an exponential scale over 2k RPM

IE: driving at 4k RPM does not use twice as much fuel as 2k.
It uses more.

Combine this information with your Liberty's shift points and you will manage just fine.


A good rule of thumb though...when the pedal touches the floor it opens up a little hole in your gas tank and the petrol fairies fly up and take all your gas away.

EDIT: sorry I forgot to answer your question...
You are better of accelerating at a decent rate up to 2nd gear at least. then deal with the 2k rule.

You are right about being too slow as being bad. Since the fuel efficiency vs rpm graph is a parabola , you can darn well bet that driving at 700 RPM will give you less than a 1/3 the mileage youll get around 2k.

OMG sleep time.

 

[2003KJ]

Well, I've noticed that by running only BP Regular 87, and trying not to rev over 2500 when taking off, i've been getting 17-18mpg all city with the a/c on. Not sure why BP gas is giving me better results, but i'm not complaining.

I've also done a tune up a few months ago, but i've got alot more miles on mine than you do (currently 33K, at the time of the tune up, about 27K).

 

[hyde]

I love how RPM suddenly drops after keeping the foot steady on the gas, doing about 40-50. If you keep driving at that range it will give you a very good mileage, thinking you dont suddenly change speed or do a lot of revving at slower speeds. Funny thing, If you let go of gas RPM increases thinking it has to drop into lower gear..

As for high RPM, more mpg, I tried the same thing, I noticed that my miles to the tank increased when I went much faster, around 70-80s for the same distance as opposed to going at 40-50.. Maybe because after speeding you have to let go of the gas and it cruises for a longer time.. There might be a funny equasion. I am not sure but Jeep seems to gulp more gas at "optimal" speeds.. :-s or standing still. I am not sure how long Jeep will last idle'ing but It's gotta be the worst car to drive on congested roads.

 

[BluPhant]

Back in the day I did some experimentation using the instant MPG feature on the EVIC and driving on the highway. While this is totally not a scientific observation, I've found that ~67mph gives me the best MPG.

As always, Your Results May Vary

-Blu

 

[hyde]

~67mph gives me the best MPG

You mean while coasting..

I hated that instant mpg, I would find myself looking at it while driving to see what is the best style, and cursing people in front of my for slowing down because me mpg was way up during coast.. So it is a good anger build-up if you get stuck to it. =;

 

[jfortier777]

The short novel I wrote above based around the 2k rpm magical number is based on the specs of our 3.7L motor, and not a general rule for any other vehicle/engine.

Other engines have different ideal RPM ranges. 2k is just the best for our engines. It does not apply while towing either.

I'll have to do some searching for the graph from DC. Its out there somewhere.

 

[BluPhant]

....lets put it this way, setting cruise control at 67mph, for me, gives me about the best mpg I can get over time. This is based on highway miles, not totally flat, but not climbing mountains or anything either.

 

[Se7enLC]

Do you guys think that there is an idea set of shift points?

I've been accelerating from 2k to 3k in each gear, ending up in 6th at 65mph at just over 2k (I think 2.2k was the magic rpm number). Recently I tried instead accelerating from 1k to 2k in each gear, only passing 2k when I got to highway speed. Acceleration is less peppy, but I think it's more fuel efficient. What does everyone else with a stick-shift have for shift points?

 

[Marlon_JB2]

Well, I've noticed that by running only BP Regular 87, and trying not to rev over 2500 when taking off, i've been getting 17-18mpg all city with the a/c on. Not sure why BP gas is giving me better results, but i'm not complaining.

I've also done a tune up a few months ago, but i've got alot more miles on mine than you do (currently 33K, at the time of the tune up, about 27K).

That was exactly my good-mileage secret with the 3.7L. I got a lot of people telling me that I was full of crap though. I didn't care. As you can see, it DOES work.

You just don't go too fast out of the stop, but who cares?

 

[Corwyyn]

I love how RPM suddenly drops after keeping the foot steady on the gas, doing about 40-50.

That's the overdrive kicking in. Try turning the overdrive off and see if it makes a difference (little button on the side of the shifter).

As far as accelleration goes, I think constant accelleration is also important; if you floor the gas to get up to speed then let off you are wasting more fuel than if you do a constant run up to speed. And look at it this way - I have a friend who has an '03 Xterra and the BEST he is able to get is around 18 on the highway. I can consistently get 21-22 on the freeway at 75 with the A/C on \/

 

[hyde]

I know about overdrive, time to time I turn it off and watch engine compress and slow the jeep down. It is really interesting. Also I use it when I need to accellarate and O/D seems to hold me back, I just flip it off and off it goes..

 

[Eddo]

The short novel I wrote above based around the 2k rpm magical number is based on the specs of our 3.7L motor, and not a general rule for any other vehicle/engine.

Other engines have different ideal RPM ranges. 2k is just the best for our engines. It does not apply while towing either.

I'll have to do some searching for the graph from DC. Its out there somewhere.

That is just engine efficiency. Other factors such as air drag and rolling resistance make a HUGE contribution to observed miles per gallon. More than even engine efficiency is alot of cases. Engine efficiency is only one factor contributing to gas mileage.

 

[jfortier777]

The short novel I wrote above based around the 2k rpm magical number is based on the specs of our 3.7L motor, and not a general rule for any other vehicle/engine.

Other engines have different ideal RPM ranges. 2k is just the best for our engines. It does not apply while towing either.

I'll have to do some searching for the graph from DC. Its out there somewhere.

That is just engine efficiency. Other factors such as air drag and rolling resistance make a HUGE contribution to observed miles per gallon. More than even engine efficiency is alot of cases. Engine efficiency is only one factor contributing to gas mileage.

Please allow me to correct myself
ENGINE EFFICIENY IN A JEEP LIBERTY. EQUIPPED WITH A 3.7L ENGINE.

I am NOT accounting for factors such as hills, tornados, hurricanes in luisianna, snow, rain, bull bars, larger tires, rotten vegetables, bricks, mindlessly long arrangements of words without meaning, or anything along those lines... my reference is to that of a stock liberty with little to no alteration to an ideal driving enviroment. All other calculations are expected to be made by the driver in each particular situation, and compensated for accordingly.

 

[Eddo]

The short novel I wrote above based around the 2k rpm magical number is based on the specs of our 3.7L motor, and not a general rule for any other vehicle/engine.

Other engines have different ideal RPM ranges. 2k is just the best for our engines. It does not apply while towing either.

I'll have to do some searching for the graph from DC. Its out there somewhere.

That is just engine efficiency. Other factors such as air drag and rolling resistance make a HUGE contribution to observed miles per gallon. More than even engine efficiency is alot of cases. Engine efficiency is only one factor contributing to gas mileage.

Please allow me to correct myself
ENGINE EFFICIENY IN A JEEP LIBERTY. EQUIPPED WITH A 3.7L ENGINE.

I am NOT accounting for factors such as hills, tornados, hurricanes in luisianna, snow, rain, bull bars, larger tires, rotten vegetables, bricks, mindlessly long arrangements of words without meaning, or anything along those lines... my reference is to that of a stock liberty with little to no alteration to an ideal driving enviroment. All other calculations are expected to be made by the driver in each particular situation, and compensated for accordingly.

All I am saying is that you really can't equate engine efficiency to gas mileage. Gas mileage is determined by much more than engine efficiency.

 

[Trodo]

Just on a side note, my best mileage from "name" brands of gas goes like this.

Exxon/Mobil (best mileage returns)
Chevron (Almost as good as Exxon)
Shell (Decent returns)
Arco (nothing great)
Costco Brand (it' getting bad)
76 (worst mileage returns)

Just my 2 cents.

 

[2003KJ]

Yes I too have noticed the Costco gas quality getting worse. Whats up with that?

 

[MoladoGuy]

I have a local gas station that prices 87 and 89 the same. I was going to them a lot but continued to find myself hitting 200+ and low gas light. I guess its how the gas burns or something because I started going to Mobile/Exxon and I am now hitting 225.

I never thought going to a different gas would help. But it looks as if it does.....

 

[JeepJeepster]

Gosh, if I do not go over 2k rpm, it takes forever to get up to 60. What do you all think this thing has in it? The I-6 4.0? I try to stay under 2.5rpms, but gosh 3k is so much better. Then theres 4k, oh wait, this is a gas mileage thread. :-$

 

[hyde]

Gosh, if I do not go over 2k rpm, it takes forever to get up to 60.

You're really not saving if you are trying to get up to 60 by keeping it under 2k. Let it roll for 3-4 seconds and get upto 50 then let it stay constant. You will be either burning same amount of gas, or just a little more, since the distance and the time it takes to get to 60 should be almost equivelent to simply letting it go over 2k and drop later on.