Lesson 1: It ain't cheap. If you're thinking about baking up a gas-to-diesel conversion at home kids, plan on having some dough. It's not as simple as changing an oil filter, so be prepared to spend a lot of your time if you're a skilled mechanic or spend a lot of your money hiring one if you're not.
Lesson 2: It ain't easy. Even transplanting a diesel engine from the same manufacturer as your vehicle (i.e. a BMW diesel going into a BMW vehicle) requires re-wiring a rat's nest of nerve endings. Not for the faint of heart.
Lesson 3: It takes longer than you think. Fabricating, locating or ordering special parts introduces weeks of delays. Tracking down fitment or wiring bugs takes even longer.
Lesson 4: Choose your mechanic carefully if you're not doing the work yourself. My first mechanic (highly recommended by others) turned out to be a dud (I'll spare you the gory details) and never completed the installation work. This necessitated a long tow truck trip to get the comatose BMW to another shop.
Read the rest of the adventure after the jump.
To begin at the beginning, the idea of a vegetable oil powered 3 Series began with my BMW 524td, a midsize diesel sedan. I appreciated its smoothness and 39 mpg highway economy, but it was hefting more weight than the engine could easily handle and it was only able to burn a B20 biodiesel blend - a "semi-alternative" fuel in my view. At 3200 lbs., it could stand to lose a few pounds in the pursuit of higher performance and I wanted to go all the way in the alternative fuel department. So I got to thinking. I used to own a sweet 1987 BMW 325e about 10 years back (yeah, I broke down and indulged myself in a gas car once in a while instead of a diesel - but I didn't inhale while I was driving it, honest). The 325e had an ideal balance of handling, performance, and economy. Hmm. Wouldn't it be a gas (pun intended) to drop a diesel into the 3 Series body and run it on straight vegetable oil? Compared to the 524td, the lighter weight and stick shift of an E30 would push the performance envelope. OK, we're not talking Corvette levels here - I mean the late-'80s diesel performance envelope. What could be simpler? Ah, fools rush in where diesel angels fear to tread. As you may have already guessed, things didn't quite go according to plan. What was supposed to take about 8 weeks in my fantasy world ended up taking 20 months in the real world. Would I do it again? < insert maniacal chuckle> Do you really have to ask? But I'm getting ahead of myself. Let's back up to the starting line.
Unbeknownst to me during my initial musings, BMW had already produced a European market diesel E30 in the late '80s, the 324td (those clever devils). In 1987 it sported 115 turbocharged diesel horses - the same power plant as the U.S. spec 524td. OK, this was auspicious. It seemed clear that a determined owner like yours truly could roll his or her own Euro 324td by judiciously dipping into the BMW factory parts bin. If BMW wasn't importing a 2007 diesel 3 series, I reckoned I could give them a hand. I'd build one out of old U.S. version parts starting with a gas E30 chassis. There is a precedent for this Frankenstein approach. In the '80s, Ford equipped the Lincoln Continental with the BMW diesel. The Vixen Motor Company of Pontiac, Michigan (1986-89) dropped the same engine into a sleek motor home body (Cd of 0.26). The Vixen 21TD would reward you with 34 mpg at 55 mph and fit neatly in your garage. This BMW diesel-powered motor coach is now a cult classic. If the BMW diesel had found a home in a motor home, why not in a U.S. spec E30 sedan?
What's the lightest possible E30 chassis? Stateside, the humble 318 circa 1984-86 tips the scales at a mere 2400 lbs. as a two door. Perfect. Here was a solid foundation. Out goes the 4-cylinder gas engine. Now things got interesting. The 6-cylinder diesel engine weighs 278 lbs. A real porker compared to the bantam 180 lbs. of the 1.8L 4-cylinder in the stock 318i. Time to avoid the bratwurst, and hit the SlimFast. I decided to toss the air conditioning compressor and condenser (shaves off 45 lbs.), dump the spare tire and jack (hey, working without a net nets a 35 lbs. savings), go with a carbon fiber hood (saves 15 lbs.), and relocate the 40 lb. battery to the trunk. If I could keep the old Bavarian beer belly from spilling over the beltline and tip the scales at 2700 lbs. or less (500 lbs. lighter than a 524td), I'd really have something. Heck, almost Mini class.
The chart below illustrates the benefits of weight control. The ersatz 324td fares well against its 1985 stable mates and even holds it own against a contemporary diesel, the Jeep Liberty CRD and a 2007 gas newcomer, the Honda Fit. Note that the output of the M21 diesel is within a whisker of the M20 gas engine's in the 325e.
Get a car. Get a diesel engine. Combine the two. Simple recipe. I located and purchased a 1985 BMW 318 two-door sedan in North Carolina. $ 1500 cash. I stumbled onto a 2.4L turbodiesel six cylinder engine that had done service in a (no kidding) diesel-engined racecar owned by a long time BMW fanatic. It was previously blessed by being raced on biodiesel fuel so I figured it was a good omen for my prospective veggie oil conversion. Sorta like having Lance Armstrong offer to donate his heart and lungs to you. I jumped on it like a pack of relatives on a Thanksgiving turkey.
As I mentioned earlier, my first mechanic failed to deliver the goods. It was an ugly divorce. Deliverance in my darkest hour came in the form of one John Negus of Larchmere Imports in Cleveland, Ohio, an independent BMW repair shop. It was a cruel twist of fate I discovered John and his minions practically in my backyard about 9 months after the E30 was in the clutches of that other guy who shall remain nameless. Timing, like a timing belt, is everything.
I'll spare you the blow-by-blow of the gas-to-diesel-to-veg-oil conversion process and give you the capsule summary of weeks of head scratching, component matching and wrench turning.
The gas engine, tranny, differential, air conditioning, stock dashboard, and rear drum brakes were gone. In their place were a turbodiesel engine, a front strut tower brace, a 5 speed out of a 325e, stiffer and lower springs (to support the extra weight of the diesel and improve handling), a 2.79 rear end, a diesel dash and instrument package, plus 260 mm rear disc brakes for stopping power. The 2.79 final drive takes advantage of the M21 engine's low torque peak of 2400 rpm. I'm turning about 1900 rpms at 60 mph. If you convert a gas car or truck to diesel, be sure to match your rear gear set to the lower rpms of the diesel engine you install. Auxiliary VDO gauges to monitor coolant temp, VO temp, vacuum/pressure (to detect blockage in the VO filter), and fuel level in the VO tank were installed in the center console. Otherwise, the interior is completely stock.
Major components for the vegetable oil fuel system came from PlantDrive, Golden Fuel Systems and VegPower Systems and Supply. An extra heated tank for the VO was bolted into the trunk between the wheel wells (the stock diesel tank was retained). A fuel filter for the VO was added, plus additional heating for the VO in the engine compartment before it's injected into the engine. A motorized valve to enable switching from regular diesel to VO and back was added to the engine compartment. It's simple, it works, and it ain't rocket science. You can use virgin oil or filtered, waste vegetable oil. Take your pick.
Rubber meets road; vegetable oil hits fan. As of this writing, I'm still breaking the engine in so the jury is out on final mileage and acceleration numbers for this 324td. Preliminary results are promising. It trumps the 39 mpg I get in the 524td by a long shot. On a recent 1,500 mile shakedown cruise, I pegged an honest 50.2 mpg overall at a steady 60 mph. High was 52.1 mpg and low 49.3 mpg. Take that, plug-in hybrids. The slightly heavier Euro 324td was supposedly good for a 11.6 second 0-60 time and 40 mpg on the highway. Haven't timed the 0-60 acceleration yet, but it definitely feels quicker than my 524td. The plant oil system performs like it should. No dramatics, just a faint aroma of cooking oil wafting down the road.
As most of you readers know, project cars are never done with a capital "D". There's always one more modification, one more adjustment, or more component swap. For now at least, the car is done with a small "d". That's done enough for me. Despite a rocky start, the project was very satisfying. Yup, I'd do again. Now if I can just get my mitts on BMW's diesel V-8 and a really BIG pry bar, I'm sure with some gentle persuasion, it could fit in.