Hey From Montana, New Owner, New to Jeeps

[cribbj]

Just purchased an '07 Wrangler Unlimited X in Houston and drove it to Montana for a "shakedown" road trip. In summary: Wow...... (in a bad way).

First of all, I discovered it was only getting 9 MPG out on the highway, so we could only get 125-160 miles per tank. "Experts" claimed it was because of the 35" offroad tires, but I noticed the engine RPM was 3000 @ 70-75 which seems high to me, so I'm leaning toward the gearing being wrong for highway driving. By contrast, my '04 Durango with a 5.7 Hemi was getting 18 MPG @ 70-75 and engine RPM was only 2000.

Then it started puking coolant from the rear of engine bay around Buffalo WY so I bought 4 gals of coolant, put 2 in immediately & we limped into Sheridan while adding coolant every 10 miles or so, then left it with the dealer Sheridan Motors. Next day they diagnosed it as a broken clip holding heater hoses to firewall. As it was Xmas Day, they patched it up & we were on our way.

Next, about 10 miles from home the tranny started slipping in "D" and I could only go maybe 5-10 miles and would have to pull over & let it cool off before continuing. Oddly enough, I noticed it only slips in "D" but not "2". 2WD or 4WD there's no difference.

That's my introduction to Jeeps, LOL. I bought it for us to have a 2nd car here in a remote area of MT and at this point, it's sitting outside and I'm pondering whether to keep it or just set the dam thing on fire as it's been nothing but trouble so far....

 

[Dirty Dog]

Just purchased an '07 Wrangler Unlimited X in Houston and drove it to Montana for a "shakedown" road trip.

I think most people would say buying a used vehicle and immediately driving it 1700 miles without going through a few basic things first is inadvisable.

First of all, I discovered it was only getting 9 MPG out on the highway, so we could only get 125-160 miles per tank. "Experts" claimed it was because of the 35" offroad tires, but I noticed the engine RPM was 3000 @ 70-75 which seems high to me, so I'm leaning toward the gearing being wrong for highway driving.

The experts were right. Swapping on a set of 35" tires without regearing is going to make your already underpowered (200HP brand new, and no doubt less now) engine perform even worse. The Rubicon has 4.10 gears. The X has 3.73 or (even worse) 3.21 gears. With 35's, you need to be at 4.56 or lower.

Next, about 10 miles from home the tranny started slipping in "D" and I could only go maybe 5-10 miles and would have to pull over & let it cool off before continuing. Oddly enough, I noticed it only slips in "D" but not "2". 2WD or 4WD there's no difference.

Nothing really odd about it. Your poor, overworked transmission has no doubt been gear hunting and spending an inordinate amount of time in 2nd and 3rd gear instead of overdrive. Which means more heat being generated. Heat kills automatic transmissions. You need a new one, or at least a rebuild.

 

[BLACKJKU]

Just purchased an '07 Wrangler Unlimited X in Houston and drove it to Montana for a "shakedown" road trip. In summary: Wow...... (in a bad way).

First of all, I discovered it was only getting 9 MPG out on the highway, so we could only get 125-160 miles per tank. "Experts" claimed it was because of the 35" offroad tires, but I noticed the engine RPM was 3000 @ 70-75 which seems high to me, so I'm leaning toward the gearing being wrong for highway driving. By contrast, my '04 Durango with a 5.7 Hemi was getting 18 MPG @ 70-75 and engine RPM was only 2000.

Then it started puking coolant from the rear of engine bay around Buffalo WY so I bought 4 gals of coolant, put 2 in immediately & we limped into Sheridan while adding coolant every 10 miles or so, then left it with the dealer Sheridan Motors. Next day they diagnosed it as a broken clip holding heater hoses to firewall. As it was Xmas Day, they patched it up & we were on our way.

Next, about 10 miles from home the tranny started slipping in "D" and I could only go maybe 5-10 miles and would have to pull over & let it cool off before continuing. Oddly enough, I noticed it only slips in "D" but not "2". 2WD or 4WD there's no difference.

That's my introduction to Jeeps, LOL. I bought it for us to have a 2nd car here in a remote area of MT and at this point, it's sitting outside and I'm pondering whether to keep it or just set the dam thing on fire as it's been nothing but trouble so far....

Typical story of someone buying a well used Jeep. If it was mine i'd drop a Chevy engine and trans in it and you'll be good.

 

[cribbj]

I think most people would say buying a used vehicle and immediately driving it 1700 miles without going through a few basic things first is inadvisable.

The experts were right. Swapping on a set of 35" tires without regearing is going to make your already underpowered (200HP brand new, and no doubt less now) engine perform even worse. The Rubicon has 4.10 gears. The X has 3.73 or (even worse) 3.21 gears. With 35's, you need to be at 4.56 or lower.

Nothing really odd about it. Your poor, overworked transmission has no doubt been gear hunting and spending an inordinate amount of time in 2nd and 3rd gear instead of overdrive. Which means more heat being generated. Heat kills automatic transmissions. You need a new one, or at least a rebuild.

Supposedly it was "gone through" by the seller who is a well known Jeep specialist in Houston, and who knew we were embarking on a very long road trip.

I've always believed that taller tires lower engine RPM, all other things being equal, and give better gas mileage, so it must be the gearing that is responsible for the horrible MPG. And I agree, this 3.8 engine is sooooo underpowered.


The Chevy engine & tranny swap suggested by BlackJKU sounds like the most reasonable way forward.... That or 5 gals of gas & a match.... I'll be doing some research in the "Builds" section of this forum. But why Chevy engine/tranny? Why not stay Mopar and use a 5.7 Hemi or similar? Is the Chevy swap that much easier/cost effective?

 

[BLACKJKU]

Supposedly it was "gone through" by the seller who is a well known Jeep specialist in Houston, and who knew we were embarking on a very long road trip.

I've always believed that taller tires lower engine RPM, all other things being equal, and give better gas mileage, so it must be the gearing that is responsible for the horrible MPG. And I agree, this 3.8 engine is sooooo underpowered.


The Chevy engine & tranny swap suggested by BlackJKU sounds like the most reasonable way forward.... That or 5 gals of gas & a match.... I'll be doing some research in the "Builds" section of this forum. But why Chevy engine/tranny? Why not stay Mopar and use a 5.7 Hemi or similar? Is the Chevy swap that much easier/cost effective?

Also the speedometer might not have been recalibrated after the tire swap.

If you put another Chrysler engine and trans along with there electronics will you be gaining anything.

GM you could go carburated engine and Hydraulic trans, or Aftermarket Throttle body Kit.

 

[cribbj]

Also the speedometer might not have been recalibrated after the tire swap.

Speedo is bang on according to GPS

If you put another Chrysler engine and trans along with there electronics will you be gaining anything.

Dunno, Maybe ease of swap with another CDJR product? I'm talking out my *ss here because I really don't know. Need to research the other builds.

GM you could go carburated engine and Hydraulic trans, or Aftermarket Throttle body Kit.

No interest in converting to a carb, particularly since the car will be operated regularly anywhere from sea level to 9500 feet above sea level.

What's your advice on regearing if I do an engine/tranny swap?

 

[tJKrider]

but I noticed the engine RPM was 3000 @ 70-75 which seems high to me

Seems high for OEM gears based on this chart for 70mph. 35s and a 5.86 would be about 3000rpm at 75mph:

 

[Dirty Dog]

Supposedly it was "gone through" by the seller who is a well known Jeep specialist in Houston, and who knew we were embarking on a very long road trip.

You actually believe what a seller tells you?

I've always believed that taller tires lower engine RPM, all other things being equal, and give better gas mileage, so it must be the gearing that is responsible for the horrible MPG. And I agree, this 3.8 engine is sooooo underpowered.

All other things are never equal. Taller tires change your effective final ratio. Lower RPM doesn't necessarily equate to better mileage. You've got an engine making less than 200HP and a narrow power band in a vehicle with the aerodynamics of a barn and a weight of well over 4000 pounds.

The Chevy engine & tranny swap suggested by BlackJKU sounds like the most reasonable way forward.... That or 5 gals of gas & a match.... I'll be doing some research in the "Builds" section of this forum. But why Chevy engine/tranny? Why not stay Mopar and use a 5.7 Hemi or similar? Is the Chevy swap that much easier/cost effective?

LS swaps are the most common, therefore the easiest to get parts for, therefore generally less expensive. But less expensive is a relative term. A properly done LS swap is going to cost $20,000. Assuming you do the entire job yourself. Drop it off and have it done and you're looking at more like $40,000. You can do it for less yourself if you use junkyard parts, but used parts (as you've just experienced) are a gamble.
Since you're starting with an X, a V8 swap would require an engine, transmission, transfer case, axles, and driveshafts. You cannot reasonably expect the little twigs the use for axles in the D30/35 to hold up to a V8.

 

[BLACKJKU]

Speedo is bang on according to GPS

Dunno, Maybe ease of swap with another CDJR product? I'm talking out my *ss here because I really don't know. Need to research the other builds.

No interest in converting to a carb, particularly since the car will be operated regularly anywhere from sea level to 9500 feet above sea level.

What's your advice on regearing if I do an engine/tranny swap?

Your Jeep sounds like mine when I bought it with 35's on it, it has 3.21 gears. I'll bet that's what yours has also.

No matter what engine it will have if it doesn't have the proper gearing you'll have problems.

 

[tJKrider]

First of all, I discovered it was only getting 9 MPG out on the highway,

Guessing this is because your trans is creating more friction/heat and significantly increasing the overall driveline loss. Pushing 35" tires is directional worse as well, even with the correct gear.

Trans will need a rebuild, or get a reman trans installed. I'll bet you find it drives way better in this config. You will at least be using the engine to its potential. Right now your making the engine work harder to overcome the deficiency of the transmission.

 

[cribbj]

Seems high for OEM gears based on this chart for 70mph. 35s and a 5.86 would be about 3000rpm at 75mph:


View attachment 125802

Oops, still learning this forum format.....

 

[cribbj]

Your Jeep sounds like mine when I bought it with 35's on it, it has 3.21 gears. I'll bet that's what yours has also.

No matter what engine it will have if it doesn't have the proper gearing you'll have problems.

How to identify which gears I have?

 

[cribbj]

You actually believe what a seller tells you?

LOL, no not quite that naive for most sellers, but yes for this particular seller.

All other things are never equal. Taller tires change your effective final ratio. Lower RPM doesn't necessarily equate to better mileage. You've got an engine making less than 200HP and a narrow power band in a vehicle with the aerodynamics of a barn and a weight of well over 4000 pounds.

LS swaps are the most common, therefore the easiest to get parts for, therefore generally less expensive. But less expensive is a relative term. A properly done LS swap is going to cost $20,000. Assuming you do the entire job yourself. Drop it off and have it done and you're looking at more like $40,000. You can do it for less yourself if you use junkyard parts, but used parts (as you've just experienced) are a gamble.
Since you're starting with an X, a V8 swap would require an engine, transmission, transfer case, axles, and driveshafts. You cannot reasonably expect the little twigs the use for axles in the D30/35 to hold up to a V8.

Wow..... so $$$$ to fix just the tranny issue and $$$$$ for the swap. There goes my home remodeling budget....

 

[cribbj]

Oops, still learning this forum format. Haven't learned how to quote multiple posts yet.....

 

[Dirty Dog]

How to identify which gears I have?

Put the rear end on jack stands. Use chalk/crayon/whatever to mark the drive shaft. Spin one of the rear tires. Count how many revolutions the driveshaft makes for each revolution of the tire.

 

[Dirty Dog]

LOL, no not quite that naive for most sellers, but yes for this particular seller.

Guess that'll teach you...

Wow..... so $$$$ to fix just the tranny issue and $$$$$ for the swap. There goes my home remodeling budget....

Most people who want to do a V8 swap would start with a Rubicon. Because it already has a stronger transfer case and D44 axles. Starting with an X makes it more expensive.

 

[cribbj]

Put the rear end on jack stands. Use chalk/crayon/whatever to mark the drive shaft. Spin one of the rear tires. Count how many revolutions the driveshaft makes for each revolution of the tire.

Any way to tell from the VIN or stickers on/in the vehicle? Right now it's sitting in a foot of snow and the nearest facility with a lift or jack stands is 1.5 hours away....

 

[cribbj]

Guess that'll teach you...

Yup.....

Most people who want to do a V8 swap would start with a Rubicon. Because it already has a stronger transfer case and D44 axles. Starting with an X makes it more expensive.

I always get a kick out of buying a "new" car & joining a new forum to learn about it and in the process discover I bought exactly the wrong model to do the things needed to make it right.

 

[Dirty Dog]

Any way to tell from the VIN or stickers on/in the vehicle? Right now it's sitting in a foot of snow and the nearest facility with a lift or jack stands is 1.5 hours away....

Yes and no. You can run the VIN, and there is usually a metal tag on the differential that indicates what the OEM gears were, but you cannot be sure that you have OEM gears.

 

[Dirty Dog]

Yup.....

I always get a kick out of buying a "new" car & joining a new forum to learn about it and in the process discover I bought exactly the wrong model to do the things needed to make it right.

You did, if you bought that as a hardcore off roader or with the intention of doing a V8 swap. If you just plan on driving it, then it sounds like you just need to regear and rebuild your transmission. And the regearing is mostly an issue for highway driving. If you're intended use is city speeds, you can probably get away without the gear swap. At least for now.