WJ Jeep Grand Cherokee sucess, is relative aparantly

[Tezzating]

Hey guys, I just wanted to gripe with some folks who'd understand.. For 2 years now my wifes complained about her Pontiac Sunfire and how she wants a Jeep SUV. So I traded off her Sunfire for a 2000 Grand Cherokee Laredo, 6 cylinder + 4 speed auto & 4x4.

Serviced the diff's with synthetic 80W90, trans with synth ATF+4, engine with synth Rotella oil, new spark plugs, intake cleaned out, fresh air filter, removed roof rack and 35PSI in the tires.

EPA is 14 City, 19 Highway. ACTUAL is 16.2 City, 22.8 Highway.

To me thats awesome gains considering there's no aero, no retuning or anything else just maintenance. To her its "terrible".

Its never occured to her going to an engine with 2 more cylinders, double the capacity, a 4 speed auto instead of 5 speed manual, extra transmission (tranfser case), two more driven wheels and extra 1500lbs of vehicle might have a negative effect on fuel economy.

The good news is, she's a bit more interested in driving efficiently now. So on the road trip yesterday we discussed and practiced drafting techniques and picking smoothest lines and such.

[comptiger5000]

I've gotten 23-24 mpg at 60mph out of my mom's almost identical 4.0 WJ (hers has Quadra-drive and 3.73 gears). My friend has one also (standard 3.55 gearing) and has pulled just about 25 out of it (before he lifted it).

Your city mileage is actually pretty good. In what I'd consider city, I've never seen more than 14 or so out of one of those. For what the vehicle is, and how capable they are off-road, etc, the mpg isn't too bad. Of course, compared to an econobox, it still sucks.

Drafting helps greatly on the highway with these, being that the aerodynamics are pretty bad. According to the instant mpg display on my mom's, drafting a semi about 70-80 feet back at 65mph is worth 4 - 5 mpg gain. Unfortunately, my V8 one only sees 2 mpg or so from this, as it's got a lot more engine, and the gearing isn't any taller, so it's already below the efficient part of its load curve.

[Tezzating]

Thanks for the feedback ! Its good to know our results are comparable to others. TBH I'm sure once we have 2 foot of snow (Hello from Canada !) she'll forget all about the extra $40 a month in gas..

I think highway speeds there's a speed at which we'd enjoy greatest efficiency. The above result was gained at an average of 75mph, doing 65mph would be better I think.

I've been looking at the front end and will make some changes which will help with highway:
- Someones chopped the inner guards, probably to fit a larger tire, but thats gotta be bad for aero.
- The grills for fog lamps are open, so I'll fill those when I fix the inner guards
- I saw a thread with a guy running an XJ on here, he gained MPG by blocking 5 of the 7 grill vents (Canadian winter coming, so this isnt a bad idea either way !)

I'm swapping in an electric fan on my truck and if that works out good, I'm going to swap the Jeeps too.

[comptiger5000]

The inner wheel-well guards may or may not make much difference, as they're not particularly exposed. Blocking the fog light holes would be worth it though.

That Jeep should already have an electric fan. If it has a mech fan, then it has both (tow package), and you're fine to pull the mech fan and run just the electric.

Also, be careful with grill blocking in warm weather, as the grille was made huge on these things for a reason.

[Tezzating]

Originally Posted by comptiger5000

The inner wheel-well guards may or may not make much difference, as they're not particularly exposed. Blocking the fog light holes would be worth it though.

That Jeep should already have an electric fan. If it has a mech fan, then it has both (tow package), and you're fine to pull the mech fan and run just the electric.

Also, be careful with grill blocking in warm weather, as the grille was made huge on these things for a reason.

Yes its got a tow package fitted, and has the electric fan. I've already deleted the wiring for the trailer, and have ben considering removing the tow hitch. So only the tow package models had the crank fan ? Thats good news ! I'll remove the tow hitch, crank fan and change the thermo-stat & coolant this weekend in that case

[mloveland78]

Sorry to resurrect an old thread but you should under no circumstance remove the tow hitch from your Jeep. They became part of a federal recall for the jeep Cherokee. Chrysler had to install the tow hitch to prevent a condition where the gas tank explodes when the vehicle is hit from behind. This was and is a big safety concern with these vehicles. The tow hitch protects the gas tank. Hopefully you already found this out on your own and are safe and sound.

[mwilliamshs]

Originally Posted by mloveland78

Sorry to resurrect an old thread but you should under no circumstance remove the tow hitch from your Jeep. They became part of a federal recall for the jeep Cherokee. Chrysler had to install the tow hitch to prevent a condition where the gas tank explodes when the vehicle is hit from behind. This was and is a big safety concern with these vehicles. The tow hitch protects the gas tank. Hopefully you already found this out on your own and are safe and sound.

WRONG.

1993-98 Grand Cherokee (WJ) and 2002-07 Liberty (LJ) model Jeeps were the sole subjects of a 2013 Chrysler recall involving gas tanks and trailer hitches prompted by an NHTSA investigation. The OP's Jeep is a 2000 Grand Cherokee (ZJ), so not involved at all in this. No Cherokee (XJ) Jeeps were recalled.

Originally Posted by Tezzating

Yes its got a tow package fitted, and has the electric fan. I've already deleted the wiring for the trailer, and have been considering removing the tow hitch. So only the tow package models had the crank fan? Thats good news ! I'll remove the tow hitch, crank fan and change the thermo-stat & coolant this weekend in that case

Yes, tow-package-equipped 4.0L WJs (base, Sport, Laredo) have a mechanical fan and others do not (never seen one on a 5.2L either). This fan is bolted to the water pump, not the crank. Shorter studs to retain the water pump pulley were needed in my case (98 5.9L Limited) but with the little I-6 your experience may differ.

A trailer hitch (steel tube under the back bumper) and a tow package are very different. Any vehicle may have a hitch. A tow package includes other equipment like engine/transmission coolers, different radiators/fans, suspension enhancements, electrical upgrades (relays for additional lighting demands, etc). That all of course varies from one vehicle to another, but you cannot buy and bolt on a "tow package" in an hour whereas that's pretty feasible with a "hitch".

[mwilliamshs]

Originally Posted by Tezzating

...a 2000 Grand Cherokee Laredo, 6 cylinder + 4 speed auto & 4x4.

Serviced the diff's with synthetic 80W90...engine with synth Rotella oil...

Did you use Shell Rotella T6 Full-Synthetic? I ask because I spent some time debating what oil to run in my own cast iron I-6 recently, a Ford 4.9, and as much as I've always liked Rotella in my diesel trucks, tractors, dozers, etc and a 1951 Dodge 235 I-6, I just couldn't bring myself to pour it into a motor that I plan to run as long as possible and get good mileage from. The only weight of T6 (full-synthetic) I've ever seen is 5W-40 and the only T5 (synthetic-blend) is 15W-40, neither of which are suitable for either of our old-school style engines, in my opinion, and that of Mother Mopar and Father Ford.

Chrysler specifies 10W-30 for your motor and Ford specifies 5W-20 for mine. I don't know your geography so a 5W might be appropriate a portion of the year if you're way up North but other than extreme winter weather (and really only for initial starting after prolonged dormancy in sub-zero conditions) a 5W is too light of an oil for these motors. Consider this a dual-damnation if you proceed with grille blocking. That being said, a 10W-30 and a 5W-30 will behave exactly the same when hot and a 5W-30 and a 5W-50 will behave exactly the same way when cold. (XW-Y means X cold and Y hot, neither impacts the other outside their respective temperature ranges)

That 5W would be good (second only to a 0W in low temp flow) in extreme cold, no doubt about it but that 40 would be detrimental to FE at anything above extreme cold so that oil and mpg just don't mix.

Chrysler deemed the low-temp protection of 10 weight oil sufficient for your motor (again extreme northern cold not-withstanding) and the high-temp protection of 30 weight oil sufficient. I can see improving on the cold protection as a benefit to minimize engine wear on wintry starts but using the heavier oil (40), which warms up slower, adds drag, and will cause an increase in oil temperature.

I've rambled on here to say this: use whatever oil you want but please be smart about it and share them smarts with me, cuz I'm genuinely interested in ecomodding an engine similar to yours. FYI: my research (BITOG, Motorcraft, Fordsix forum, FTE forums, etc) lead me to use 5W-30 synthetic but I think 5W-20 would work fine and that the 30 is due to the heavy-duty applications this engine was popular in, which differ from my light-duty uses. I also use Rislone ZDDP additive due to mine being a flat-tappet motor.

[Fat Charlie]

Just a correction: The 93-99 is the ZJ, the 00-04 is the WJ.

It is correct that the problem (and recall) covers the 93-99 and not the 00-04, and that's what really matters.

[mwilliamshs]

You're right. Those idiosyncratic nomenclatures get me every time. My buddy David named his son Noah just to irritate my CDO