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My Neighbor's 35 MPG Jeep Diesel Conversion

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Nolen Hart writes about buying and maintaining cars, among other things.

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Why a Diesel Jeep?

I myself own a 1997 Jeep Wrangler with a four-cylinder gas engine and five-speed manual transmission.

Around town it gets about 16 mpg and on the highway about 20. While this isn't as bad as a Hummer, I think it should do better, especially for such a light vehicle.

Jeeps are fun and versatile vehicles but one thing they don't have going for them in terms of fuel mileage is their boxy shape. Jeeps are aerodynamically like a brick. They have to push a lot of air aside and this really eats up gas mileage.

How can a Jeep get better mileage? You might lower one down a bit (though I shudder at the thought; I mean why have a Jeep then?). Or you could change out the engine as my neighbor Jim recently did.

Diesel engines are a much more efficient way of using fuel. That is why they are the engine of choice in most of the cars on the road in Europe, where fuel costs three times or more what it does here in the US. New technologies are available which can reduce particulate emissions from diesel engines, yet most automakers are now more focused on moving toward the EV market. Four-wheel drive Jeeps are made for use off road, and since there are no EV charging stations "out there", internal combustion engines are still the best choice at this point for off-road vehicles.

My Neighbor's Jeep

Jim has the kind of shop that I envy, a twenty by forty-foot domed barn with a rolling lift that he can use to remove engines with. His shop has the works, air compressors, lots of tools, and even body work equipment.

His latest project was to take the engine out of a 2002 diesel Jetta and put it in his Jeep Wrangler. Over the course of a year I visited with my friend as he took out the original engine and meticulously reinstalled it with the diesel engine, removed it again to change out part of the transmission and finally ride with him on the Jeep's maiden voyage.

I'm not 100% up on all of the details involved, but one of the reasons he had to remove the new engine was to modify the transfer case because of differences in the torque of the diesel compared to the old gas engine.

The Jetta engine fits inside the Jeep's engine compartment just fine, with some room to spare, on newly modified motor mounts. The fuel tank, flushed and cleaned is the same one as the Jeep had before. I drove around in it with him and it sounded almost the same, with a little throatier diesel growl on hills, which it crawled up like a champ.

Jim claims that he has checked it numerous times by dividing the number of miles driven by the amount needed to top off the tank and he is getting at least 35 MPG on the highway, sometimes more, and around 30 MPG city.

Here in our area diesel is costing about 70 cents more than gas per gallon, but even at that rate the increase in fuel economy is still a big improvement, not to mention the extended cruising range, which can come in handy if Jeeping in remote areas. Jim claims that the diesel Jetta Wrangler conversion handles hills in four-wheel drive much better thanks to improved low-end torque versus the old gasoline engine.

I think Jim just may be on to something with his Jeep - Jetta diesel conversion. He is talking about starting a diesel Jeep conversion company and I might just be his first customer.

An Update

My friend and neighbor passed a way a while back, a few months after I wrote this article. His son drives his old converted diesel Jeep now. I really think my friend was on to something good. It is too bad that too many states have such tough laws against converting a vehicle to diesel. I would advise anyone who wants to do a similar diesel Jeep conversion to first find out what the state laws, as well as federal emission laws are regarding that subject and if this might pose any problems for vehicle licensing later down the road.

Update: Finally, a Diesel Option

Jeep is now finally offering the option of a V6 EcoDiesel, an upgrade available on 2021 models costing $4,000. This engine upgrade also requires an eight-speed automatic that adds another $2,000 to the sticker price. Early reviews from this package so far have been very good, as low end torque produced by the EcoDiesel is very high and fuel economy is reportedly excellent.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

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