Reader Rides: A 1992 Jeep Wrangler Diesel Conversion

2012-08-23This story was written by Tom Hansen and sent in to us. Want to share your own alt-fuel conversion with the world? Click the “Contact Us” button at the top right-hand corner of the page.

When the guy selling 92 YJ to me said, “You sure you don’t want to talk to the price down lower?” I should have known something was up. But I wanted it, it was lifted with oversize tires and a rhino lined interior. My 17-year-old inexperienced self had no idea of the problems associated with buying a Jeep that was already beat up.

Then I decided to convert it to diesel.

I started the long process of getting the 4-cylinder, 1992 Jeep Wrangler up and runnin I had fixed and replaced most everything on it except its blown 4-cylinder. Originally I wanted to bore and rebuild it, but after all that work it still wouldn’t have been anything special. I wanted my Jeep to be unique, as a true Jeep should be. With the guidance of my father, a professional mechanic, and the resources available to young Mechanical Engineering students, like myself, I knew I could tackle a challenging build.

The easiest way to do this is to just take it all apart.

Until I saw my first diesel Jeep at a show in PA I had never considered diesel because of its lack of throttle and the obvious difficulty of the conversion. But driving home that day I had a brain-blast; the diesel cycle is awesome and the effort is totally worth it. Not only could I save money with better mileage and possibly even get free fuel from businesses, but I would have more power at low rpm where the Jeep most needed it.

With a little research, I found the Mercedes OM617 turbodiesel engine was a perfect match. This motor uses indirect injection (a must for running straight vegetable oil), has a strong vacuum pump for power steering, and has no computer to program. Additionally, it has a cast iron head and block, similar max rpm and peak horsepower to the 4-clyinder, and it would outlast the rest of the car by tens of thousands of miles. And most importantly, it would fit in the engine bay perfectly. There was information all over the internet for troubleshooting this engine as well as running it off veggie oil so my confidence in the feasibility of this project grew.

As the research went on I found photos from a number of OM617 transplant projects. I knew if they could do it- I could do it. To make the long and complicated project short, I bought an 85’ Mercedes 300D out of a junkyard for $800, ripped out the motor and rebuilt it. Then I bought a bigger transmission from another junkyard, rebuilt it, and pulled an engine out of an ’95 Dodge Dakota in yet another junkyard to get to the bell housing (the Dakota housing had the starter in a location where I would no longer be next to the turbo).

A clean fit.
The Mercedes motor looks right at home in the Jeep.

I worked countless hours at school designing and machining the adapting parts to get the asymmetric 6 bolt flywheel to fit the symmetric 12 bolt crankshaft and V8 size bell mount to the inline 5 block; made engine mounts. I bolted the motor in and got it started with WD-40 and ether, fully rewired the Jeep like the hot rod it, made custom transmission mount and cross member and did a whole bunch of other stuff. Then I got to the fun part; I drove it.

As for veggie conversion, this project needs nothing besides extra filters and good oil (not old, water content low, and no additional waste). The Jeep is more fun to drive than ever. I can chug up mild grades in 2nd gear no throttle and sound like a badass doing it. Not only is it easier for the tire to turn but it gets almost double the original fuel mileage (originally 14mpg on regular gas, now gets mid 20s).

It will be many years before the conversion makes financial sense but the education I gained and the people I met already made the conversion worth every penny, and now my Jeep is truly unique.

Christopher DeMorro

A writer and gearhead who loves all things automotive, from hybrids to HEMIs, can be found wrenching or writing- or else, he's running, because he's one of those crazy people who gets enjoyment from running insane distances.