Diesel Swap??

im looking into doing a diesel swap, maybe a 4bt, the Mercedes 5cyl, or maybe the renault 2.1 that xj's got.. my question sits more in with how will diesel cope with working much lower gears? im running 5.13's with 37's and im looking to go diesel for better fuel economy as well as more power and so on... but im not very experienced with diesel and im curious of what I should be looking for in the diesel engine for my jeep... i know the 4bt is pretty common, any other ideas?

Mpeckham22 said:

im looking into doing a diesel swap, maybe a 4bt, the Mercedes 5cyl, or maybe the renault 2.1 that xj's got.. my question sits more in with how will diesel cope with working much lower gears? im running 5.13's with 37's and im looking to go diesel for better fuel economy as well as more power and so on... but im not very experienced with diesel and im curious of what I should be looking for in the diesel engine for my jeep... i know the 4bt is pretty common, any other ideas?

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what kind of fuel economy are you getting now? i'm not doing the math to figure your final drive ratio, but what RPM range are you using in your day to day driving? is it revving easily or are you lugging the engine as it accelerates? dont be afraid to let the 4.0L rev a bit. my 90 XJ 4.0L AX-15 rig improved the fuel economy when i went with the lift, 33s and 4.56s. RPMs around 3000 at highway speeds and it breathed easily.
the expense of swapping your drive train will far exceed the $$ savings at the pump. maybe you need deeper gears or a set of smaller street tires to get some mileage back?
adjust your driving style or buy a Corolla for DD stuff.

Typically Mercedes cars with diesel engines have more "normal" gearing than other diesel setups. The Mercedes engine was designed to rev and behave like a gas engine.

Check out the red lines of the engines that you are considering.

Also, consider what RPM range you normally cruise at and see if that works with the engine you are considering. Most diesel engines like to be in the 1600-1800 rpm range for cruising, the Merc maybe a touch more like 2200-2400.

These numbers are from memory so verify before you commit money.

Also, if you are doing the diesel because you like diesels and/or you need a new engine anyway then keep going. If you are chasing fuel economy to save money at the pump then don't bother.

2¢

sidriptide said:

dont be afraid to let the 4.0L rev a bit.

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I agree, that's what the rev limiter is for. My engine sees frequent 20-30 second redline runs in the sand during desert season and it does very well.

The 2.1 doesnt have much power and if you put a newer mb motor in the cost of the swap would not be worth effort. You definitely dont want any old NA diesel motors. If you truly wanted the 4bt the best option, there is sum options you have to get in the 150 to 200hp range with minimal effort. You could change the governor springs to up your redline to about 3.8k but it would still be happiest cruising at 2 to 2200rpm.

4bt. Loudest rattling heaviest slowest thing possible. I can't wait to put one in black jeep!!! Oh yeah, hoodstack too

could always go with bigger gas tank. or ls1-2-3

2.1 renault... underpowered, rare, and hard to find parts for, from what I hear.

4BT... too tall and heavy to really be worth putting in an XJ without a stupid amount of lift. Not saying this from experience because I haven't done it, but that's why I wouldn't.

OM615 series merc... kinda underpowered I hear. But I know a guy who has one in his CJ and likes it. Oh, and I know where there is one, complete (at least as of a few weeks ago, it was still there Saturday when I looked but I didn't check closely) under the hood of a donor car somewhere near here, in a junkyard that's gonna be doing a 50% off sale Sunday. Wanna go pull an engine? It's naturally aspirated... so you're gonna have to swap a turbo onto it. But you can probably grab the whole engine package for under 250 bucks.

VW TDI... at least IMO they are a bit underpowered for a jeep, in stock form. Can be tuned up though. Nice motors, good fuel economy, well built.

Cummins A2300 series... smallish, more similarly sized to the 4.0, I have almost no info on them but it's something to look into. Kinda gutless. 4cyl, a 6cyl version would be cool but I have no idea if they make them.