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My best fuel mileage ever!!

Rusty from Cleveland

NAXJA Forum User
Location
Cleveland, TN
99 xj, 4.0, auto, stock except for modified airbox and Amsoil oil-wetted air filter, Castrol Syntec 10w30, mobil 1 syn in diffs and transfer case. I usually get around 18.5 mpg on my interstate trips and occasionally get up to 21 on secondary highways with approx 55 mph speeds, but while on vacation (interstate driving and a little secondary highway driving with minimal stops) I got 20.9 MPG on the way from Cleveland, TN to Destin, FL and then 22.5 from FL back to TN. I could not beleive it! There was plenty of 75+ MPH driving each way, but had a little less stop and go on the way back from FL. Anyway, I used Marvel Mystery Oil on the trip, both ways and got better fuel mileage on the way down than usual, and my best fuel mileage ever on the way back. I had heard good reports on MMO in the past but wow! Anyway, I know there have been some discussions of MMO on here in the past, but wanted to give MMO a little praise this time. I know the $2.97 I spent on the big bottle of MMO offset the $1.77 - $1.97 per gallon of gas that I had to buy over the 1000 mile round trip, and I didn't even use the whole bottle of MMO. Anwyay, I am impressed. I may not use it around town so much, but I am gonna plan to have plenty of MMO for any trip that I go on. Anyone else on here had good or bad experiences using MMO? FYI I only used it in my fuel at the 4oz per 10 gal recommendation...........Rusty
 
I can actually get 23+ with my 98, 4.0, 5sp, lt235's and 3:07's, the catch is I need to keep a steady 75+ in 5th or 65+ in 4th. I very rarely get to use 5th around here unless I'm headed down to philly area on the turnpike or into NJ on interstate 80. I'm now back up to 19-20 in my normal driving on back roads but very rarely do I get out of 3rd on them. I was scheduled to get re-regeard yesterday but my A/C has been problamatic again, won't take any more 134a so I had to cancel till next month, taking it in tonight and we are going to drain the system and refill it correctly. I think I have added too many freon/oil top off cans to compenstate for my slow leak and as a result have too much pag oil in there. As funny as it sounds if I drive with the windows open my milage suffers badly on the hiway from the wind, much better milage with the A/C on and windows closed. I'm also about ready to pull the surco safari rack off when I don't need it on there because I know thats at least a 1mpg gas eater.
 
RichP said:
I'm also about ready to pull the surco safari rack off when I don't need it on there because I know thats at least a 1mpg gas eater.

when i lost my surco rack my mileage didn't change. i usually stay between 18-20 at highway speeds and 15-18 city.
 
Rusty from Cleveland said:
I usually get around 18.5 mpg on my interstate trips and occasionally get up to 21 on secondary highways with approx 55 mph speeds, but while on vacation (interstate driving and a little secondary highway driving with minimal stops) I got 20.9 MPG on the way from Cleveland, TN to Destin, FL and then 22.5 from FL back to TN. I could not beleive it! There was plenty of 75+ MPH driving each way, but had a little less stop and go on the way back from FL. Anyway, I used Marvel Mystery Oil on the trip, both ways and got better fuel mileage on the way down than usual, and my best fuel mileage ever on the way back.

Well... not being a big fan of snake oils (not that I'm pointin' any fingers!)... Have you considered that this is perhaps the first time your XJ has done
such a long all-highway trip? Have you considered that GA and FLA,
probably have different gasoline formulations than TN?

Also... to reinforce RichP's statement: It is a commonly perpetrated MYTH
(which has been bandied about quite a lot by the media in the past couple
of months) that "cars lose 1mpg per ten MPH over 55". Bull. Every car
is geared differently, has different aerodynamics, and is generally set-up
for different dynamics. Some get better mileage at 75 than 55. [At least
that's the story I'm stickin' with, Officer!]

Den
 
I was getting at least 45 miles per gallon driving down from grand junction...All downhill. Dont even have to put the foot on the gas to cruise at 65mph :jester:
 
My best is 21 coming from Joshua Tree to Oceanside CA. Its about a 140 mile trip. Half the tank was spent on the way up, the other half was spent on the way back. Stock except for a K&N drop in replacement and I usually just use whatever oil is used at the oil change shop. I don't have the time to get in and do it myself very often.
 
DenLip said:
... It is a commonly perpetrated MYTH
(which has been bandied about quite a lot by the media in the past couple
of months) that "cars lose 1mpg per ten MPH over 55". Bull. Every car
is geared differently, has different aerodynamics, and is generally set-up
for different dynamics. Some get better mileage at 75 than 55.Den

I'd like to see your example of a car that gets better mileage at 75 than at 55.
 
MaXJohnson said:
I'd like to see your example of a car that gets better mileage at 75 than at 55.
Hey, ya never know, a car might have gearing setup that 4th is too high for 75 so your buzzing along with the engine revved high but 5th is a bit too low bogging the engine so you gotta give it more gas. That'd be a crappy gearing set up, but there's probably one out there. I know my Mom's car (92 Lumina Euro) does just as good at 75 as it does at 55. She has a very high overdrive.
 
BlackSport96 said:
Hey, ya never know, a car might have gearing setup that 4th is too high for 75 so your buzzing along with the engine revved high but 5th is a bit too low bogging the engine so you gotta give it more gas. That'd be a crappy gearing set up, but there's probably one out there. I know my Mom's car (92 Lumina Euro) does just as good at 75 as it does at 55. She has a very high overdrive.

ANY stock 4.0L, 5speed, 3:07 geared XJ that gets it tires bumped up from p215 or p225 to LT235's or 30x9.50's and it's duplicatable... My milage is much better at 75mph + in 5th than 65 in 5th. Now if I keep it in 4th and do 65 then it is the same pretty much.
 
BlackSport96 said:
Hey, ya never know, a car might have gearing setup that 4th is too high for 75 so your buzzing along with the engine revved high but 5th is a bit too low bogging the engine so you gotta give it more gas. That'd be a crappy gearing set up, but there's probably one out there. I know my Mom's car (92 Lumina Euro) does just as good at 75 as it does at 55. She has a very high overdrive.

'zactly.

My example is a (dearly departed) '97 Dodge Stratus with the Neon's
2.0 motor on a 5-speed. At 55 in 5th, I had to downshift to climb the
slightest rise. But at 70, she was settled in around 2700 rpm, and
was far enough up the torque curve to handle most highway grades.

And it was aerodynamic enough that wind resistance wasn't much of a
concern. I was quite happy to get 35mpg from a largish midsize sedan.
And with a tank designed for the V6/auto combo, I had almost 550 miles
of range on a tankful!

The Jetta I replaced it with was terrible at 70+... because it was a
turbo, and was "on the boost" for the whole trip. Got like 7mpg less
than the Stratus on the open road... with similar weight, aerodynamics,
and only a small power advantage "as measured" ... but she'd scoot
in a hurry if you punched it at 70mph in 5th.....

That's what I like about the XJ... there is no gas mileage to speak of,
so why bother to talk about it? :)

Den
 
RichP said:
...if I drive with the windows open my milage suffers badly on the hiway from the wind, much better milage with the A/C on and windows closed. .

Do you have those little dark plastic hoods--what are they called?--that fit over the windows? I think they might be the most useful accessory I know of. You can keep windows open 2-3 inches w/no draft & no rain blowing or dripping in. They've made it possible for me to keep air circulating in the car around the clock (to get rid of a sickening air-freshener smell) w/o having to check the weather forecast.

Keeping windows open even a crack in rain was impossible in my Trooper. The door pockets were always full of soggy stuck-together maps.

I should think they'd virtually eliminate the mpg drag of open windows if 2-3 inches is enough for you. They look nice & they seem to be incredibly durable. These have been on mine for all its 8 years & look like new.
 
The vent shades, never got around to ordering them. I do keep my drivers window cracked and inch or so, also helps with the A/C on. I just never wanted to spend the money on them.
 
Snake Oil...Well I don't know. Was just stating that it (MMO) "appeared" worked for me. Generally on similar long trips I have gotten 18-19 mpg w/ out MMO while travelling 75-80 mph most of the time. I would think that a slight change from 70-75 versus 75-80 might make up some of the difference since our XJ's have the aerodynamics of a brick as some have said. Anyway, it is hard to configure all the dynamics into the equation. I am sure that my usual trip from TN to Atlanta and then to Myrtle Beach being altered to TN to AL to Destin, FL has changed the amount of elevation changes that occured on the other route. I have often wondered about those ventshades that have been mentioned and even those headlight covers that cover the whole "pocket" that our headlights are mounted in as far as making the XJ a tiny but more aerodynamic. FYI in the trip I had probably 850 lbs worth of people and cargo plus a hitch haul on the rear and I am also minus the rubber flap that prevents water/mud spray into the engine compartment (but I have a used front skid that I eventually plan to install) . I also ran my A/C the whole time on the 22.5mpg trip with it on the cool fresh air setting. Hey is there any difference between the amount of time the A/C compressor runs on each A/C setting? Seems like I heard that the setting that I had it on runs the compressor a little less, but I haven't paid much attn. One more thing that i did on my 20.9 mpg section is that I pulled the fuse to my elec fan (I only do this when I know that I have no stop and go and the engine can stay plenty cool and I keep the fuse pulled out during the coldest winder months) but I left it in on the 22.5 mpg trip. The reason I pull the fuse is that when the A/C kicks on, of course the fan does too and it puts more pull on the alternator and causes un-needed wear on the elec fan too. Anyway, I think that my city mileage sucks because I rarely get above 15 in stricty town driving. I only have a 1 mile commute to my work and I live on a pretty big hill too, so I have to mash it pretty good to get up my street and my driveway (living on a hill works well for me being a ham radio operator though giving me better communication on VHF/UHF). Living in town with eternal-holding traffic lights doesn't help either. Oh well, just another 2 cents...But I really do think that the MMO or maybe any other light machine oil may help mileage a little bit when used as a top cylinder lubricant.....Rusty
 
A 1 mile commute and you DRIVE, man thats the severest duty that you can put an engine thru. That engine NEVER warms up, never comes out of cold loop or has the opportunity to burn off moisture from condensation in the oil. If any of my vehicles are cold I try not to run them untill I have enough places to go so that I can run it at least 20 min, it takes 10-15 min for the OIL to reach operating temp. I had a 7am service call this morning, the agency is 8 min away so I left early and took the long route, grabbed a bagel and drove the extra 20 min. You must get a phenomenal amount of carbon build up in there.
 
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