Disputing gas saving tips

[WB9YZU]

here are a couple gas saving tips for ya. TDI, Honda, Mini i could go on. you'll never catch me in a prius(not because its a hybrid)the damn thing is UGLY!!!!!!!

Well, you could also bicycle, walk or use the bus.

Get a little scooter to get around (They use them year round on campus!)

Get a motorcycle.

But this is an XJ forum, so I assumed we were meant to reference gas saving tips for an XJ. Yes/No?

Ron

 

[5-90]

You may want to rethink some of that paragraph. There is no 55mph National Speedlimit, it was repealed in 95'. As it went the 55mph law was effective because the manufactures of the time did two things right, they downsized the cars and regeared them to the 55mph speed limit. It worked and saved countless of lives.

You are right, each vehicle I have owned had a sweet spot where the speed and fuel efficiency curves intersected to give you a speed where the vehicle was most fuel efficient. Personally I found that running 75 though Nebraska in my XJ is not the most fuel efficient, but makes the trip shorter

One thing I have not heard talk of here is the subject of oil. Use as light an engine oil you can get away with. I run 10W30 in all my Jeeps. When I raced, I used 5W20 synthetic with out issue. Same with gear oil; I use 75W Synthetic in the axles.

I also have heard nothing about tires. Pizza cutter tires with an AT design work better for gas mileage that fat MTs because of less rolling resistance and less mass to get rolling.

Ron

True - I'd forgotten that they repealed that. Still, how many problems have been solved by passing a law? I've always wondered about that line of thinking...

 

[Ecomike]

Fuel saving tips?

Cruise (steady-state) at or near the torque peak of your engine. RENIX cruises best at 2800-3000rpm, HO slightly higher (say, 3000-3200rpm.) If this means not using overdrive, don't use overdrive. It will help.

5-90,

Everything I have read here at says the best mileage is achieved with the 4.0 and AW4 auto tranny, at 2,300 to 2,400 rpm, with stock stuff, 3.51 rear end and stock tires in 4th gear.

So far my experience is showing my best mileage at 2,200 rpm, 55 mph, in 4th gear, with my 87 renix, 4.0 AW4 package. That includes mileage tests with the old defective ground wires, bad O2 sensor and bad TPS, and with everthing working properly the last 6 months using the new TPS, O2 sensor and new grounds. My mileage drops significantly at 2,800 rpm and higher for cruising.

If I recall corectly gearing and tire size affects this issue as well.

 

[5-90]

5-90,

Everything I have read here at says the best mileage is achieved with the 4.0 and AW4 auto tranny, at 2,300 to 2,400 rpm, with stock stuff, 3.51 rear end and stock tires in 4th gear.

So far my experience is showing my best mileage at 2,200 rpm, 55 mph, in 4th gear, with my 87 renix, 4.0 AW4 package. That includes mileage tests with the old defective ground wires, bad O2 sensor and bad TPS, and with everthing working properly the last 6 months using the new TPS, O2 sensor and new grounds. My mileage drops significantly at 2,800 rpm and higher for cruising.

If I recall corectly gearing and tire size affects this issue as well.

Which is why I specify a given crankshaft speed. I wonder why the flyer, tho? I do better cruising at 2800 or so than I have at 2400 or so (88XJ/3.07/31's.) I suppose my 88 could just be weird - it's also the one that doesn't like to have a thermostat installed (even with a full system flush and a brand spankin' new radiator, it will overheat with any thermostat installed. Runs fine without one. Third vehicle like that I've run across in about 30 years...)

So, it could just be a flyer from "normal variation" - but it's still going to be better than cruising at the 1800-2000rpm or so that they tend to be geared for in OD with a manual.

But yes, gearing and tyre size do effect fuel economy. Most production vehicles, however, are still geared for too low of a crankshaft speed at freeway cruise, once you check the torque charts. We just have the advantage of a broad, flat torque "peak" over most other vehicles. It does still have a bit of a "sweet spot", tho...

 

[falcon556]

But yes, gearing and tyre size do effect fuel economy.

When you go to a larger tire, the odometer will record less miles.
That will appear as a drop in mileage.
I lost a couple of mpg when I went to larger tires, I think from the tread design mostly.

 

[FlexdXJ]

Well, you could also bicycle, walk or use the bus.

Get a little scooter to get around (They use them year round on campus!)

Get a motorcycle.

But this is an XJ forum, so I assumed we were meant to reference gas saving tips for an XJ. Yes/No?

Ron

:dunno:

yeah i am just joking man didn't mean anything by it. I just think that talking about gas saving tips for a Cherokee is rediculous. the best thing i can put out there is buy a stocker with a 5 spd and drive it then have another jeep as the play toy. keep it tuned up and running good and you are good for around 20 mpg highway

 

[5-90]

When you go to a larger tire, the odometer will record less miles.
That will appear as a drop in mileage.
I lost a couple of mpg when I went to larger tires, I think from the tread design mostly.

True, and the speedo isn't 100% accurate. But, you can find mileposts, and figure a correction for freeway speeds, then apply that to your odo and mileage calculations as well.

 

[Ecomike]

Which is why I specify a given crankshaft speed. I wonder why the flyer, tho? I do better cruising at 2800 or so than I have at 2400 or so (88XJ/3.07/31's.) I suppose my 88 could just be weird - it's also the one that doesn't like to have a thermostat installed (even with a full system flush and a brand spankin' new radiator, it will overheat with any thermostat installed. Runs fine without one. Third vehicle like that I've run across in about 30 years...)


So, it could just be a flyer from "normal variation" - but it's still going to be better than cruising at the 1800-2000rpm or so that they tend to be geared for in OD with a manual.

But yes, gearing and tyre size do effect fuel economy. Most production vehicles, however, are still geared for too low of a crankshaft speed at freeway cruise, once you check the torque charts. We just have the advantage of a broad, flat torque "peak" over most other vehicles. It does still have a bit of a "sweet spot", tho...

You definately have lower gearing and bigger tires than I do. I have not tried doing a tank of gas at 55 mph in third gear on mine, but it seems to me that cruising should be more fuel efficient in fourth gear, OD, on a stock vehicle like mine. Yours of course has no stock rear end gearing and big tires (compared to mine) so it probably makes your sweet spot higher. So I take it the peak torque is a long nearly flat run from 2200 to 3000 rpm?

Also you have a manual tranny as I recall!!!???? The AW4 may like the lower rpm over time, mpg wise?

 

[rickolis22]

Fuel saving tips?

Cruise (steady-state) at or near the torque peak of your engine. RENIX cruises best at 2800-3000rpm, HO slightly higher (say, 3000-3200rpm.) If this means not using overdrive, don't use overdrive. It will help.

is this true? i have a 94 4.0 5 speed. i was driving on the highway doing about 80mph and my rpm was only a little over 2000. so keeping it in 4th gear on the highway and staying around 3000-3200rpm will give me better gas mileage?

 

[5-90]

You definately have lower gearing and bigger tires than I do. I have not tried doing a tank of gas at 55 mph in third gear on mine, but it seems to me that cruising should be more fuel efficient in fourth gear, OD, on a stock vehicle like mine. Yours of course has no stock rear end gearing and big tires (compared to mine) so it probably makes your sweet spot higher. So I take it the peak torque is a long nearly flat run from 2200 to 3000 rpm?

Also you have a manual tranny as I recall!!!???? The AW4 may like the lower rpm over time, mpg wise?

I have, so I actually have shorter gears (3.07) than you do (3.55.) With most tyre sizes between stock and 31-32", the 3.55 gears complement the AW4 rather well. With the five-speed, 3.07 is woefully undergeared, and overdrive is all but useless (as I have said before, I picked up somewhere around 3-4mpg when I quit using fifth gear on the freeway.)

Going to 3.55:1 axle gearing would be a step in the right direction for the manual - 3.73 would be better (and should have been done from the factory, instead of this 3.07 nonsense.)

 

[Blaine B.]

That's what those stupid "vapour recovery nozzles" are supposed to be for. But, if they're so good at vapour recovery, why for does the whole damn filling station still smell like fuel?

That, and the people who pull the hose without letting it drain down first - and end up spilling about a cupful of raw fuel on the ground. In 20 years or so, I think all the fuel I've spilled (a drop at a time) will probably fit in a coffee cup with room to spare. I see people spill more fuel than that in one go.

Heh, those vapor recovery nozzles in Cali always got me. I would wonder why no fuel would go in. Then I'd pull the pump out and the "recovery" neck would be filled with fuel, straight to the ground. Who cares though, it was a rental car.

Now on your idea about running at peak torque - I never thought about trying that. I was under the impression that lower RPM's were better for highway cruising, and I've always tried to keep them low. Next time I'm on the highway I'll run in the RPM you recommended for the H.O. and see if I notice a difference.

 

[Shorty]

if we're talking about wasted "fuel" the recovery nozzle works o.k.-- but if we're talking about wasted money-- they stink (pun intended) as they return the vapor to the dispenser (pump) AFTER you have been charged for it.

If you keep the tank close to half full (empty, for the pessimists) and fill up in the cooler times (early A.M.) you'll get to keep more of what you paid for.

 

[xjallday!]

The best thing you can do is not follow my lead and buy a 98 ZJ 5.9 Limited. Unless, of course you're American, and drive big vehicles with strong engines and don't worry so much about gas prices, then you can follow my lead and do 4 wheel burnouts and have a grand old time.

 

[TiRod]

As for the long idle time - the first point of the original poster -

I caught the Cartalk, researched the internet, and found the no-idle movement apparently came from the truck and fleet industry cutting fuel costs. A diesel idling overnight uses about a gallon an hour, and during the day can use a few more stuck at lights, parking lots, etc. The old school reason was to keep the fuel from gelling in cold temps, and because starting systems weren't so hot in the day. I know, I've gone on jumpstart calls on a 5* day in January to discover that even a dual generator setup on a wrecker won't turn over a Cat-engined OTR truck when it's that cold - even with a smudge pot under the pan for hours.

Cars had carbs then, and a little warm up was recommended to get heat to the riser under the manifold to help vaporize fuel. At the fuel costs then, it was ok, and certainly cheaper than a wrecker call and the lost time.

With fuel injection, don't bother. People warm their cars up for one basic reason - they don't know better, and to get their heater going so they'll be more comfortable at the start of their commute.

They'd be better off with a seat heater installed than wasting gas on a warm up. They are readily available from the street rod industry, warm up much quicker than the heater core, and put heat right where you need it - not the entire interior environment. You can run the system cooler, stay more alert, and be more comfortable on a longer trip.

To save on gas, I took off my useless roof rack. I have a 5X8 utility trailer to really haul stuff, and I can find my car in the lot quicker.

 

[88xjchief]

What about converting a XJ to run on hydrogen?

 

[Dest]

I get 16 MPG highway X.x

 

[MAY POP]

Another thing to mention is type of tire. My work van,a 05 chevy would get 12.5 to13.5 mpg with Firestone highway tires. The company put new Good Year Wrongler a/t on it. It instantly lost 1 to 1.5 mpg. I check mileage every tank. Tires do make a difference. Those tires cost the company big time!

 

[Ecomike]

Which is why I specify a given crankshaft speed. I wonder why the flyer, tho? I do better cruising at 2800 or so than I have at 2400 or so (88XJ/3.07/31's.) I suppose my 88 could just be weird - it's also the one that doesn't like to have a thermostat installed (even with a full system flush and a brand spankin' new radiator, it will overheat with any thermostat installed. Runs fine without one. Third vehicle like that I've run across in about 30 years...)


So, it could just be a flyer from "normal variation" - but it's still going to be better than cruising at the 1800-2000rpm or so that they tend to be geared for in OD with a manual.

But yes, gearing and tyre size do effect fuel economy. Most production vehicles, however, are still geared for too low of a crankshaft speed at freeway cruise, once you check the torque charts. We just have the advantage of a broad, flat torque "peak" over most other vehicles. It does still have a bit of a "sweet spot", tho...

Well, I am going to have to say that torque at the wheel (after all the gearing..... is also important, not just peak torque at the engine crankshaft. I don't know the math on this off the top of my head, but my highway gas mileage nearly doubled when I replaced my defective TPS. The old TPS was up-shifting the AW4 to the next higher gear at 1400 rpm, even at WOT. The new TPS is up-shifting it at 2200 to 2400 rpm at 1/10 th to 1/4th of WOT from a dead stop to 60 mph.

5-90, I tried your 3000 engine rpm highway, constant speed run at 60 mph in third gear (AW4) for 30 miles of a normal freeway commute in a normal 231.8 miles tank of gas. My prior 7 tanks of gas all ran about 15.5 mpgs +/- about .1 mpg, this last run dropped to 14.41 mpg, a huge drop considering I only tired the 3000 rpm, 60 mph, 3rd gear run for only 30 of the 131.8 miles!

In fact I could see the gas gauge moving, while the engine sucked gas at 3000 rpm!!!!!! I could actually se it eating a good 3 gallons in 30 miles!!!!! If I had to hazard a guess, I would have to say that mine gets nearly twice the mileage in 4th at 2300 and 60 mph as it does at 3000 rpm at 60 mph in third gear.

Please excuss me if I don't test an entire tank of gas at 3000 rpm on mine!

 

[MudDawg]

My experiences with fuels with ethanol are that they do in the case of my Heeps yield lower fuel mileage numbers....all three Heeps, every time.

My solution to the fuel cost issue is called Buell Blast! 70+ mpg

 

[5-90]

Well, I am going to have to say that torque at the wheel (after all the gearing..... is also important, not just peak torque at the engine crankshaft. I don't know the math on this off the top of my head, but my highway gas mileage nearly doubled when I replaced my defective TPS. The old TPS was up-shifting the AW4 to the next higher gear at 1400 rpm, even at WOT. The new TPS is up-shifting it at 2200 to 2400 rpm at 1/10 th to 1/4th of WOT from a dead stop to 60 mph.

5-90, I tried your 3000 engine rpm highway, constant speed run at 60 mph in third gear (AW4) for 30 miles of a normal freeway commute in a normal 231.8 miles tank of gas. My prior 7 tanks of gas all ran about 15.5 mpgs +/- about .1 mpg, this last run dropped to 14.41 mpg, a huge drop considering I only tired the 3000 rpm, 60 mph, 3rd gear run for only 30 of the 131.8 miles!

In fact I could see the gas gauge moving, while the engine sucked gas at 3000 rpm!!!!!! I could actually se it eating a good 3 gallons in 30 miles!!!!! If I had to hazard a guess, I would have to say that mine gets nearly twice the mileage in 4th at 2300 and 60 mph as it does at 3000 rpm at 60 mph in third gear.

Please excuss me if I don't test an entire tank of gas at 3000 rpm on mine!

Interesting. Given the same construction, the torque output of individual engines becomes a function of crankshaft speed (assuming same head/cam/breathing/...)

I get best mileage cruising at 2800-2900rpm crankshaft speed with 31s and 3.07. I still want to change the gearing (it really doesn't sit well with the transmission, it's a horrible complement to the tyres as well...) and that should end up changing the relationship between cruise speeds and crankshaft RPM - I'll have to find my notes.

However, if you were to do a longer-term test to find your "sweet spot" for crankshaft speed at cruise, I'd like to see your notes when you were done.