2001 4.0 to 2003 5.9 Magnum V8 swap

AlaskanTJ · Jul 1, 2026

Made some more progress today. I've had the engine side of the motor mounts just loosely bolted on, so I got around to tightening those up. The Advance Adapters installation instructions mention needing two spacers for the driver's side mount, but they didn't mention that the passenger side also needs a spacer. The kit only comes with two, so I had to make do with some washers to make up the extra gap on the driver side mount.

A couple days ago I checked the clearance to the radiator with the Dodge fan clutch and found that it didn't have any, so today I tried again with the 4.0 fan clutch. The depth was good, but it looks like I'll have to move the shroud down a bit to get it to line up. Does anyone know of any reason why the 4.0 fan clutch wouldn't work with the 5.9? It threaded on just fine, and the fans are the same size, so if I can use it that's one less thing I need to buy.

I also got my transmission mount adapter plate template finished today, now I just need to copy the design onto a thicker piece of steel I picked up.

AlaskanTJ · Jul 3, 2026

Adapter plate is finished

Wildman · Jul 3, 2026

AlaskanTJ said:
Made some more progress today. I've had the engine side of the motor mounts just loosely bolted on, so I got around to tightening those up. The Advance Adapters installation instructions mention needing two spacers for the driver's side mount, but they didn't mention that the passenger side also needs a spacer. The kit only comes with two, so I had to make do with some washers to make up the extra gap on the driver side mount.

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A couple days ago I checked the clearance to the radiator with the Dodge fan clutch and found that it didn't have any, so today I tried again with the 4.0 fan clutch. The depth was good, but it looks like I'll have to move the shroud down a bit to get it to line up. Does anyone know of any reason why the 4.0 fan clutch wouldn't work with the 5.9? It threaded on just fine, and the fans are the same size, so if I can use it that's one less thing I need to buy.

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I also got my transmission mount adapter plate template finished today, now I just need to copy the design onto a thicker piece of steel I picked up.

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That's interesting that your MM's don't fit properly. It must be a 03 thing? My 98 5.2 block fit and then my 98 5.9 I needed the spacers on the one side. Here's the pictures I've got from my 98 5.9 block...

Transmission adapter plate looks good.

AlaskanTJ · Jul 3, 2026

Wildman said:
That's interesting that your MM's don't fit properly. It must be a 03 thing? My 98 5.2 block fit and then my 98 5.9 I needed the spacers on the one side. Here's the pictures I've got from my 98 5.9 block...

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Transmission adapter plate looks good.

I guess it's just another thing that's different because my donor is a 3rd gen Ram.

Did you have any thoughts on the fan clutch and shroud setup? I've seen people mention using a ZJ fan setup, but that doesn't look like it'd be much different than just reusing the 4.0 fan and clutch.

Wildman · Jul 3, 2026

AlaskanTJ said:
I guess it's just another thing that's different because my donor is a 3rd gen Ram.

It always seems like it never ends...

AlaskanTJ said:
Did you have any thoughts on the fan clutch and shroud setup? I've seen people mention using a ZJ fan setup, but that doesn't look like it'd be much different than just reusing the 4.0 fan and clutch.

I'd just run the TJ setup... As long as it cools your engine and you won't know that until you get it running and work it hard.

AlaskanTJ · Jul 5, 2026

Got the shroud on fitted around the fan today. I had to cut quite a bit off on the bottom to clear the lower hose outlet and the power steering lines, but now it clears the fan with enough room to spare. The pictures aren't great, but I'll take some better ones when I take the engine back out to paint the frame and the mounts. I've got the shroud held on with self-tapping screws, and I'll still have to take it back off when I put the replacement radiator in. For now I'm going to use the stock radiator so I don't damage the new one while I'm checking fitment.

AlaskanTJ · Jul 7, 2026

Got the motor mounts and the transmission adapter plate painted today. I also mostly put the transfer case back together. Also got another picture of the shroud cut.

AlaskanTJ · Jul 10, 2026

Got a bunch more done of the last couple of days. Yesterday I got the transfer case shifter brackets installed and filled up the engine, transmission, and transfer case with their respective fluids. With everything filled up I was able to test my starter wiring, and it turned over without issue.

Today I kept at it, and got the fuel lines figured out, the wiring harness hooked up to the engine, and bolted on and hooked up the new ZJ power steering pump. I had to route the power steering lines under the steering shaft to get them away from the exhaust manifold. For the fuel line I ended up reusing the stock flexible fuel line from the Dodge, I just had to shorten the Jeep's hard line on the frame since the Dodge line is longer than the TJ one. The union I used to rejoin the barbed end of the hard line with the rest of it doesn't seem to be biting in, so I can still pull the lines apart. Oddly enough it's still sealing, but I'll have to figure out a better union later. I'm planning on setting the body back on tomorrow so I can start it, and I made sure to disconnect the SKIM today so I wouldn't forget about it. I'm still planning on wrapping the harness up, but I want to make sure everything works first before I do.

AlaskanTJ · Jul 12, 2026

I got the body set on the frame and hooked everything up for a test fire this evening. At the moment it seems I'm not getting any fuel. I suspect I might have a ground issue to, because besides the lack of pressure it's also showing empty on the dash when it shouldn't be. That's a problem for tomorrow though. For now I'm just happy it runs at all.

View: https://youtube.com/shorts/0Fl51J9O6kQ

AlaskanTJ · Jul 12, 2026

It's alive! Turned out to be a bad ground to the fuel pump, so once I grounded it properly it fired right up. I'm gonna be trying to clean up the wiring today. There's some wires that need to be connected with more than just alligator clips, and I need to figure out why I'm not getting anything from the OBD port.

View: %5BURL%5Dhttps://youtube.com/shorts/j7USSBL754c[/URL]

Wildman · Jul 12, 2026

AlaskanTJ said:
It's alive! Turned out to be a bad ground to the fuel pump, so once I grounded it properly it fired right up. I'm gonna be trying to clean up the wiring today. There's some wires that need to be connected with more than just alligator clips, and I need to figure out why I'm not getting anything from the OBD port.

View: %5BURL%5D%5BURL%5Dhttps://youtube.com/shorts/j7USSBL754c[/URL][/URL]

Congrats I know how good of a feeling that is...

NDSpeed · Jul 13, 2026

just in time for some Fall wheeling, you’ve only got what 17 days of summer left.

AlaskanTJ · Jul 15, 2026

Well I seem to have broken something. I got my harness taped and loomed over the last day, and I put the body back on today to test it. Then when I went to start it today It just turned over and my gauges weren't working. I realized I hadn't hooked up the ground to the body, but I didn't think to unhook the battery or even turn off the key while bolted it back on. It sparked a bunch while I was tightening the bolt and I heard noises from inside the cab. Now I have nothing on the dash at all. No gauges, no odometer, no turn signals, no dome light, etc. The only thing still working is the starter when I turn the key. I can't find any burnt fuses in either fuse block, so I'm at a loss here.

AlaskanTJ · Jul 16, 2026

Well I'm not entirely sure what I did to fix it, but it's working again.
View: %5BURL%5Dhttps://youtu.be/VbyMVdpyNZs[/URL]

Wildman · Jul 16, 2026

AlaskanTJ said:
Well I'm not entirely sure what I did to fix it, but it's working again.
View: %5BURL%5D%5BURL%5Dhttps://youtu.be/VbyMVdpyNZs[/URL][/URL]

That is all the matters... But try to find that loose connection or ground..... They can be a PITA out on the trail..

AlaskanTJ · Jul 16, 2026

Things I got done over the past few days:

Replaced heim joints on the front upper control arms. Old ones were completely worn out
Pressed on new Power Steering Pump Pulley. Turns out the Dodge pulley doesn't fit on the ZJ pump so I had to get a new one
Attached transmission shifter cable. It's just ziptied in place at the moment, but surprisingly the throw seems to be perfect and it appears to hit all the gears without issue. Once I get my driveshafts in I can confirm that.
Fixed OBD port. Grounds weren't wired in.
Added a connector for four wires that were otherwise going to be hardwired into the fuse box
Finished taping and looming the harness
Attached the heater hoses to the core. The stock Dodge hoses seem to work just fine here
Swapped the new radiator onto the grille. Shroud still needs to be reattached, but that will take some hand fitting, and I still need to figure out what hoses to use
Reattached the hood so I could check clearance. With the air intake clocked slightly towards the back it just barely clears the center bracing on the hood. The transmission dipstick also just barely clears.

There's still plenty of small things to do, but most of the major work is done at this point. My driveshafts from Tom Woods should be here soon, so once I wrap everything else up it'll be time to take it to an exhaust shop. I'll be having them build me a new crossover pipe while they're setting up the muffler and tailpipe.

AlaskanTJ · Jul 18, 2026

View: https://youtube.com/shorts/ByBVHQ6vvf0

View: https://youtu.be/3Benss2McAg

View: https://youtu.be/GnSJClIzMMk

Got a bunch more stuff knocked out today so I could test drive it finally

Engine, transmission, and body mounts all tightened. I didn't realize until today that I'd had my motor mounts setup wrong this whole time, and once I corrected that the fan shroud actually lined up with the holes. The higher position does mean that the hood no longer clears the air intake though.

Figured out my radiator hose setup. For the upper I cut down the stock hose to make it fit, and for the lower I used an Autozone E72347 hose which I then cut down to the right length
Installed original Dodge serpentine belt without issue
Reattached steering shaft
Filled new power steering pump
Reattached master cylinder and bled brakes
Installed new Tom Woods rear driveshaft
Topped off transmission fluid. The transmission felt a little off on the first drive. I hadn't checked the level since I cold filled it before I started the engine the first time. After I filled it up it felt normal.
Removed throttle cable from Dodge and "installed" it in the Jeep. The firewall attachment is different and the cable is too long or the stops are setup wrong or something. For the moment I used a couple sockets as spacers to hold the cable further back from the firewall, but it doesn't have full travel.

During my second test drive I discovered that my electrical short hasn't actually gone away, and the Jeep died at a stop sign and the gauges started freaking out, which is what they were doing a couple days ago when I was having issues. I'm gonna have to do some for testing to figure where I'm getting a short. I'm also gonna have to get some rear shock mount extensions because of the increased pinion angle.

AlaskanTJ · Aug 1, 2026

No pictures to attach at the moment, but I have still been working on the swap. I've had it out and driving around to see how it behaves, and so far I've found a couple of issues that will need to be dealt with. The biggest issue is that it's developed some nasty death wobble, which it didn't have before the swap. I'm guessing the extra weight probably isn't helping things there, but I haven't looked at it closely yet.

The transmission seems to mostly be behaving, except for the 1-2 upshift at WOT. If I keep the pedal to the floor it won't upshift and just bounces off the rev limiter, but if I lift a little it will shift. I did have to replace the TV cable end at the throttle body, so maybe that changed the length slightly and I just need to adjust it back.

The last big issue I've got is with the air intake setup. I ended up getting the intake hat and tube off of a 97 5.2 Dakota at the junkyard, which I was able to clamp onto the TJ airbox. The only issue there is that with the air filter in the box the engine seems to be choking out and collapsing the tube at WOT. Without the air filter in the box it has no issues though, so maybe I need some sort of high flowing air filter? Not sure if that's a thing I can get for the TJ airbox though.
Seems like this was just because of how the airbox is bungeed in right now. When I bungeed it tighter it had no issues even with the air filter installed.

On a more positive note, I've got an appointment on Tuesday to get the exhaust system built. Once that's done I'll be putting the fenders back on and it'll start looking a lot more done.

AlaskanTJ · Aug 9, 2026

I got the TJ back from the exhaust shop yesterday, and with it back it was mad dash to put everything back together in time for its first off road trip with the new engine. I also figured out that my death wobble was caused by a very loose castle nut on the frame side of the track bar, so I replaced the whole thing and it's been smooth sailing.

The Good:

Plenty of power on the highway, no issues whatsoever with passing
Stable well in excess of 65MPH, which is a big improvement from the massive driveline vibrations I had starting at 55MPH before the swap
Engine is nice and quiet, but still has a good growl to it at trail speeds
TJ 4.0 fan and fan clutch seem to work just fine cooling the engine on the trail, but 80° is probably the hottest this thing will ever see, so YMMV there. My temp gauge stayed rock solid at 210° the whole time.

The Bad:

The transmission seems to be consuming fluid on the trail. No idea where it's going as I can't see any leaks, but after a while of driving the transmission starts acting up and when I check it the dipstick is dry. I was trying to keep it topped off today once I noticed it was happening, but that can't be good for it. No issues at all on the highway though.

J20 · Aug 17, 2026

AlaskanTJ said:
I got the TJ back from the exhaust shop yesterday, and with it back it was mad dash to put everything back together in time for its first off road trip with the new engine. I also figured out that my death wobble was caused by a very loose castle nut on the frame side of the track bar, so I replaced the whole thing and it's been smooth sailing.

The Good:

Plenty of power on the highway, no issues whatsoever with passing

Stable well in excess of 65MPH, which is a big improvement from the massive driveline vibrations I had starting at 55MPH before the swap

Engine is nice and quiet, but still has a good growl to it at trail speeds

TJ 4.0 fan and fan clutch seem to work just fine cooling the engine on the trail, but 80° is probably the hottest this thing will ever see, so YMMV there. My temp gauge stayed rock solid at 210° the whole time.

The Bad:

The transmission seems to be consuming fluid on the trail. No idea where it's going as I can't see any leaks, but after a while of driving the transmission starts acting up and when I check it the dipstick is dry. I was trying to keep it topped off today once I noticed it was happening, but that can't be good for it. No issues at all on the highway though.

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How'd you end up running you exhaust? Single pipe?

2001 4.0 to 2003 5.9 Magnum V8 swap

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