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Gears for towing 5k#

F

filmxj

NAXJA Forum User
Location
Chattanooga
I've got a '98 xj with 4.0, AW-4, 3.55 gears, D-30, Ch 8 1/4, 31' all terrains, a good weight distributing hitch and an aux tranny cooler.

I've been towing a boat that is 3200# plus the trailer - and with other stuff I'm sure is pushing right up close to 5000#.

This all works reasonably well for the most part. My question is this: When towing on the interstate, I'm usually in 3rd gear. Occasionally on a gentle downhill I may nudge it into OD. The thing tows decently, but the MPG is pretty dreadful. I was thinking about going to 4.10 gears, but that would mean I would need OD unless I wound out the engine to get any kind of decent highway speed.

With my current setup I'm right at 2500 rpm in 3rd gear at 65mph. If I regeared I would be at 2889 in 3rd.

Conventional wisdom says get higher gears to make it a better tow vehicle. Am I crazy to think that towing in 3rd with these slightly tall gears is probably better for MPG and for the tranny then thiking about 4.10 gears and using overdrive?

What would you guys do? Leave well enough alone or go to shorter gears?
 
'Not trying to be a smartass, but if I regularly towed 5K, I'd buy a bigger truck. The XJ can tow 5k, but it's not really rated for it. If I was stuck with towing, on 31"s, I'd put the 4.10s in there. You'll like wheeling it better too :D
 
I personally wouldn't change gearing for the sole purpose of occassionally towing a boat because I would assume that mileage would still stink while towing after regearing. If you have other criteria for wanting to change your gears, well I suppose that might change things.
 
I can see you saying it isn't ideal for it, but the manual pretty clearly indicates that it is rated for it. I've got good trailer brakes and a weight distributing hitch.

I used to have a mid 90's 3/4 ton diesel suburban and I'm not interested in owning something like that again, but I see your point.
 
I tow a 3,000 pound bass boat with my 90 and I can't imagine towing anymore than that on the highway! Especially something that is dragging wind as well.

But I would say that the 4.10's should be about right for the 31's and towing.

Like tbburg says though, I would look into something a little heavier for regular towing, maybe a Tahoe/Yukon, Commander or Expedition. Keep the XJ for what it shines in, off-roading!
 
I've heard that the 4L-60E trannys that are in GM half ton's are pretty sketchy for towing...but then again the last GM (suburban) that I owned was pretty sketchy in it's entirety! (not trying to start a fight, that's just my experience - and a bad enough one that I'm not going there again...)
 
I have had 2 99's and a 92 all of them have towed heavy loads before. I asked the service manager (My fathers neighbor) of a jeep dealer and was told they set the rating limits for warranty purpose. I know for a fact that they will tow more and be safe doing it. I would go with the 4.10's or even 4.56 to take the stress off the transmission because every one knows thats the week link. Unless you have a d35 which you do not.

I use to tow a 24' rv with my first 99 all stock towed way better then my 92 with 31's because the gearing was correct. The 99 would go down flat highway in 4th no problem but the 92 sucked balls unless in 3rd and even then the 99 did better. I have since sold both of them and got another 99 with 31's and plan on getting another rv along with 4.56 gears when the economy gets better.

Dave
 
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I think you're about as good as it's gonna get. The Jeep may be a little different than my Crown Vic, but hauling a relatively small utility trailer, my freeway gas mileage goes from 25 normal to 15 when hauling the trailer. Dropping it out of OD into 3rd just knocks the mileage down to 10-11. It doesn't take much of a hill either to make it downshift out of OD. What I figured I would need to get better fuel mileage hauling is a computer that would let me vary the fuel mixture and timing to allow for the extra load. I don't think that turning more RPM's is the answer. You also don't want to screw up your mileage when not hauling.
 
As the others said, your mileage will still suck. Your engine and transmission will probably be happier and that's worth A LOT.

I have a '91 with the 5 speed. I went from 3.07's to 3.55's in the axles, which is roughly the same as going from 3.55 to 4.10 in an AW-4. It helped quite a bit while towing, expecially at lower speeds (AX-15). On the highway it didn't slow down as much on the hills because it was in a sweeter spot for power, but I was also producing more horsepower (and burning more gas) at a given speed going up that hill. Before, I had to give up speed...now I just keep going.

My mileage didn't measurably improve or decrease while towing my 3300# travel trailer. It was still about 10-11 mpg before I switched to a more qualified tow rig. I did see almost 2 mpg increase when not towing though! Yes, I corrected the odometer for error.:D

If you're after better gas mileage, I don't think it's going to happen. It still takes a given amount of horsepower to pull that "aerodynamically challenged" trailer through the air. My '03 Expedition with the 5.4L also gets about 10.7mpg while towing, but I'm not working it like the XJ. It pretty much loafs in OD.
 
filmxj said:
So you never had trouble towing in OD? I've always been a little afraid to. If I towed in OD I think the 4.10 gears would make sense for the highway.
Click to expand...

I never had a problem on flat land with stock tires. When I seen a hill coming I would just drop to 3rd then back to 4th at the top. When it comes to towing MPG don't mean much to me because I only to for camping and boating in the summer. If I re-member the stock 99 got about 10-11 and the 92 was around 9 maybe 10 if I was lucky.

The right gears do make a big difference. I had a 86 ford turbo diesel with a 3 spd and 4.10's got way bad mpg. Also had a 94 non-turbo with 4.10's and a 4sp got 16 towing the same rv as the jeeps did.

Dave
 
Do youself a favor get 4.56 and be done with it. I towed 4200lbs with mine stock with 3.55.. I dont know what OD was... lol.. Even with a trany cooler you pushing it with 5,000lbs. I would not want to do that for any long distance. Just extra wear and tear on it. low end gears in the axles make it easer on the trans and everything else.
 
99Redxjbuilder said:
I use to tow a 24' rv with my first 99 all stock
Click to expand...

Holy cow!!! I couldn't imagine a 24ft RV on the back of a tiny little unibody Cherokee. There's no weight to the Cherokee, getting a cross wind would kill you. One of those tandem axle Uhauls full was more than I wanted on the back of mine going down the highway. Anything larger than a utility trailer or a pop up camper and I would use a 1/2 ton truck for long distance.
 
So is the consensus that on flat ground OD is OK, shift into 3rd for hills, and go for 4.56 gears, but don't expect an improvement in gas mileage?
 
To those of you surprised about towing this much, the truth is that you know it's back there for sure, but a good weight distributing hitch and good trailer brakes take the white knuckles out of it. It handles well and stops easy in my experience. Just be very careful with very steep mountain grades - make sure you don't overheat the engine or the brakes.
 
filmxj said:
So is the consensus that on flat ground OD is OK, shift into 3rd for hills, and go for 4.56 gears, but don't expect an improvement in gas mileage?
Click to expand...

Yep. I towed a 21ft Ski sanger for 7 years with 4.10's and 31's. It did pretty good but I couldnt run the ac unless i was on flat ground. 4.56's would have been much better.
 
I never agree with anyone. So, if your going to tow a LOT. (IMO) lose the 31 and get some good 235/75 (((LTs))) or maybe a little bigger if they now make them for 15 inch rims. Braking will improve without putting big bucks into the brakes. The right tires for the job help out in many more ways then just engine RPM.
Lower her back to 2 inches of lift at the most. Put the rear sway bar back on if taken off. Get some kind of HD rad.
Don't worry so much about what gear you use. Let that slush-o-matic do it's job by picking the gear.
Change oil every 3.5k when towing.
(IMO) change trany lub every 20k
LUCK and have fun.
 
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