Fred/N0AZZ

Still working on my XJ build so driving it around town and to places having work done on it. Have checked to MPG on it a couple of times and not really pleased at all. The biggest problem is the 3.55 gears in it and the 33x12:50x15's on it still undecided on gears either 4.10 or 4.56 spool in the rear 8.25 electric locker in the D-30.

I do have it finished out with all gear for the trail front tube winch bumper with bull bar and 9.5 Superwinch, Rear HD bumper with swing out tire carrier/Hi-Lift jack mounted on it. Custom large rooftop carrier and custom frame with roof side protection/2" tube. Also in the back are tools 4 in 1 shovel/ax/hoe/hammer and recovery items for myself and my son's XJ I know its heavy.

But.....filled up yesterday and mileage had dropped from 11.5 before the rear bumper and all tools were installed to 8.3 mpg. This seems to be excessive and even a gear change will make this up. BTW the engine seems to run very well even with a small oil leak and 219,000.

Are my weight, tires, lift 3 1/2" and gears the only factor in the mpg? I would appreciate any input as to what I might other than the oblivious like gears and removing all extra weight but that is needed when on the trail.

Thanks,
Fred

ZINGGG

Your speedo gear is off by a little with the larger tires, therefore your calculations are off. You're getting slightly better than that.

Assuming you're calculating your mileage by the tripometer divided by gallons put in?

93XJLI

i averaged 15.5 highway driving cross country with my 93 with a few thou under 200k miles, 33x10.5 BFG MTs, 4.56s and an AW4. loaded weight for that trip was around 4k i believe.

Fred/N0AZZ

I feel foolish yes the speedo is 7 mph slow I knew that but a consideration I should have thought about.

The 4.56 gear you said you are running I do think helped me to make a decision for my XJ with your tire size, gear and 15 mpg. Thank you that was going to be another post I was going to post today. Mine is NOT a daily driver and will see limited road use will trailer to most places "Just in Case" .

Fred

Lead Foot

My jeep weighs 4800. D44 axles, 37.5" KM2s, 5.13 gears, 4.5" of lift. I get atleast 16mpg on the freeway.

m2carbine

Man something gotta be wrong with my rig 97 XJ 31's 3.5 lift stock gears 9 Mpg city and starting to get worse it seems.

ccooper1234

When's the last time its had a tuneup? Check for vacuum leaks. Clean Throttle body. Sea foam

XJnumero3

short term: Sea Foam, full tune up, stick with oil(DO NOT go synthetic) & consider going up to mid grade. Low grade is really really poor quality lately, if you can afford it doing these, going up in octane and keeping up with your ABCs will help ALOT.

Long term: Specter Air Intake(great sound/easier install than you'd think), New Fuel injectors (mustang fuel injectors work best but you want a 4 hole vs a 1 hole injector which is what stock is), move up to a new Throttle Body and spacer... 62mm TB is ideal, clean air intake manifold!!!, replace exhaust manifold (banks is ideal and has sales), replace o2 sensors, replace cat, replace cat back exhaust.

I've done all these steps and was pleasantly surprised to find a big increase in MPGs but overall satisfaction in engine sound and performance on/off road.

Hope it helps!

m2carbine

sorry to kinda hijack. It's been about a year since the last full tune up it has the mustang injectors 63mm TB k&n air filter ARB style snorkel the up O2 sensor is almost a year old and is NGK.I seafoam every 3 months and add fuel injector cleaner when its on sale(which is often). The cat needs to be changed I've been planning on it for a while. I want to upgrade the intake but that's gonna be a pain.

andrewmp6

Honestly i wouldn't run a spool in a daily driver it can get hairy in the rain and wear out the rear tires faster then the fronts.And how much in weight you carrying in tools and do you really needed them every day?

Fred/N0AZZ

Mine is not a daily driver this is the way it will be when "Trail Ready" with all the extra weight, recovery gear, tools misc. parts to check everything that way.

I have been running high performance SBC's on the street all over 550 hp for the last 30 yrs and a few of them just north of a 1000 hp. Every one of them has had a spool in them since I broke a Detroit Locker a number of yrs ago with only 750 hp. That was at the strip with only a 10" slick.

Fred

Fred/N0AZZ

Here again very helpful post for the "Old Man" on a 5.13 gear the most help was the tire size with it and mpg. I don't think that a 37.5 tire is in my future at this time and that much more roll out would be great for sure.

Yours is the first post on the 5.13's have you ever ran them on 33's and if so what were those numbers also do you happen to remember RPM's. I'm guessing that your engine has at the very least been rebuilt it not modified in one way or another?

Thanks,
Fred