• Welcome to For Trucks Only !

    We are a community of American Brand Pickup Truck and SUV owners. Join now! Its Free!

Better gas mileage???

MoparsOnly

MoparsOnly

The snozberries taste like snozberries.
Joined
Sep 24, 2015
Messages
371
Reaction score
99
Location
South Carolina
This is somewhat of a dodge truck question since, the vehicle in question is a 03 jeep grand cherokee. Okay, so here's the story my wife and I did a refy of my house to get out from under our private lender as well as lower our monthly nut. Anyways, we got extra money for some upgrades in the household. One of the upgrades was to get a newer car for the wifey. She use to drive an 03 jeep gc that she absolutely loved. She drives a 2010 grand caravan right now, nice but not the jeep, her words. So I purchased a 03 jeep gc with a blown 6cyl. That I'm going to replace as well as, the tranny and a anything else that needs attention. I was wondering MPG and, It's around 19 hwy. and 16 city. My question is the gearing stock is as low as 373 and as high as 411 with a 29.5" tire. If I lowered the gearing to around a 323 maybe even a 307 with roughly a 30" tire, how much would this affect take off and, passing power. Let me know your thoughts.
 
Pure guesses here, but I'd guess maybe at best a 10% boost in mileage and at least that much lost in available power. I wouldn't do it, mostly 'cause I like power on tap right away, but also she'd have to drive a whole lotta miles for a couple years to begin to break even on the expense. Unless of course you have access to unlimited funds and/or cheap parts and want to change shtuff just to change it and brag about the mileage......... But it's still gonna take a long while to break even.
 
Thanks for the input polara. It's not about just being able to do it. It's more for a bit better mileage. If I can get the hwy. to 21, 22 even 23 mpg. I'd be stoked. I do have a bit of money to do this. We owed about 50gs on the house and took 85. The idea was to take 10 and throw it down on a 2017 ford edge limited or a jeep gc. Instead since she loved her 03 so much that i'd take the 10 and re-do a 03. Almost all of our driving is hwy. because we live out in the country. I've built diff's for going fast but, never for the opposite. I was thinking of power band and how much it would be affected.
 
Most of that was the smart ass coming out of my fingers. Mostly I'm just a cheap ass old fart that wants to see my money back from any investment quickly, and a $500 gear change (which would be real inexpensive to my way of thinking) would take a lot of miles to make up the cost difference of 3-4 mpg gained. Okay, so for a 4 mpg gain at 3.00 gas, in 20,000 miles you're on the verge of break even. So it comes back to how much driving will she do with it, and what kind of driving is it? You state country driving, but is that 4 lane divided hwy or 2 lane twisty country hwy? (If the latter I'd not give up any response time for mileage.)
 
So you presently do not know what gears are in the 03 purchased? I do not imagine she does much off road driving so are rock crawler slow speeds needed? Doubt it!
I do not think going higher than 3:23 gears would gain much either and you more than likely would drop it out of its power band.
Quite honestly instead of changing gears I would go with taller tires if body clearance will allow it. Even taller than 30". Maybe a 32 or 33.
It would be lots simpler changing back if the desired results were not achieved.
 
I'm pretty sure they are 373's. Yes. I could imagine it now my wife running thru the local mud bog. Going to anything bigger than a 30 would mean lift kit time and, that is not my wife. She was born and raised manhattenite. I'm a old long island boy living in South Carolina about an hours drive from myrtle beach and, loving it. That is what I was thinking on the power band. As for the hwy it's a four lane pretty much straight shot to her job.
 
The only real answer here is - what specifically did your wife like about the GC over the van? Now, will your anticipated changes alter that experience in any significant way? We had a 95 GC years ago and it was a great vehicle, I've driven bunches of vans but none of them came close to giving me the pleasure driving the GC did. With less power I don't know how well I would have liked it, but you're not trying to make me happy, are you?

By the way, when I got rid of the GC 17 years ago it made me a real happy man, but the ex wife went with the Jeep. :happy:

It sounds like this is a make your wife happy story (smart man) so make sure she's as happy as expected. :praying:
 
Do you know what the OD ratio is? I am not familiar with what transmission that would have.
 
Polara, Your a wise man. I live by happy wife happy life, Yes dear and, nothing honey opps forgot one other, your right I'm wrong. Don't get me wrong we both love the van, lots of room, very peppy but, very expensive to fix. The trans has started to act up and, engine management problems here and there. My wife has super bad knee problems so, she likes to not have to climb in or fall in (car). The jeep is like perfect height for her. She loved the comfort of the chairs as well as, ride quality. I also know the jeep 4L exceptionally well. When I first got back from college (a very longtime ago) Denver Auto & Diesel. I went to work for a Jeep dealership. When I started they were just starting to transition to the 4L and, they haven't really changed much since then. The only thing that has changed are the t.case and tranny. As for the OD ratio it's .69 for the 42re. I'm also going to do a few minor upgrades to the engine.
 
Aha!! I hadn't considered the 4.0 I6, was thinking mostly of the 5.2. I would guess that the I6 may have a little better torque low down so the impact of your changes may not be quite so drastic as what I was thinking. And the GC is very comfy especially on a longer trip.
 
Yup. they stopped putting the 318 in them around 98. Then the 4.7 came out. Nice engine it's actually a poly head valve and port arrangement with cams on top. I'm looking for durability, easy to fix as well as, cheap. You are also correct on the 4L having good low end torque.
 
That would put it real close to 2000 rpm at a 70 even with 3.94 rears. What engine mods will increase mpg? Maybe things like better air intake a small turbo & intercooler.
 
That is just about spot on. a gc with a 4L, 373, 29.5" tire at 70 comes out to 2082. Now lets change it to a 323 and 30" it comes out to 1773. The same thing with a 307 =1685. We all know the lower the rpm the less the engine works and, the less gas used. For the upgrades: minor port match, smooth out intake as well as, air intake box system, glyptal block & head for windage reduction, oil air separator and, a higher flowing exhaust header & cat delete and, better injectors. That should do it. I may have forgotten something but, that is what I can think of off the top of my head.
 
Lower engine rpms only works to a point. Get them to low and the engine works harder to get it down the road and will use more gas than at higher rpms. You need to keep it in its happy zone. I am not sure were that would be with your set up.
Case in point. My 68 Charge RT (440 long gone - has a 383 with more power) likes to run in the 3400 rpm range with 4:10 gears that puts it in and about 70 mph. With 3:23 gears it drop the rpms to about 2600 rpms at 70 mph. Plugs fowl, the engine complains gas mileage goes south. Just not a good thing. Push it backup to 3400 rpms and all is well again other than running a very expensive 85 to 90 mph if I get picked up.
 
My dad broke his leg many moons ago, and I got to drive him around. He was going back to school to.become a patent lawyer, or something that didn't pan out. Anyway, I was his driver and we used his Toyota Corolla. Getting my driving chops as a parts delivery guy, I never learned how to drive like a grandma. My get there yesterday approach actually got me a few miles to the gallon better mileage. We figured that I got the engine up to speed faster, and the wasted fuel getting there, was recouped, mileage-wise, by the longer continuous cruising speed.

In my daily driver '08 Avenger, it doesn't seem to matter what driving style I use, the mileage always stays the same.
 
Yup, that is my style get to cruise as fast as possible and, just lock it in. My wife is kind of like that ben stiller character from along came polly. I kid around and call her my little risk assessor. I've tried to explain how getting to cruising speed faster works better than crawling to cruising speed. I believe my way is not only better for mpg but, for keeping all the other pieces in proper order - heavier on the gas = more load = more heat to burn off more carbon.
 
As long as components have had the proper time to warm up and done using some common since. No reason to hammer a cold engine to death.
 
But of coarse. Me, I would never do that. Just kidding. Totally agree with that but, cold in south carolina? It was 75 yesterday. Hell, last week we had a few days hit 80. Me I'd rather 50-55 and sunny year round. It's going to be a really bad summer down here (110-120 heat index) can't wait.:arghh:
 
You must log in or register to reply here.
Back
Top