This article is written by guest writer Ricky Nietubicz on his experience with a Mercedes powered by vegetable oil.

Over the years, I’ve always gazed somewhat longingly at BMW and Mercedes vehicles from the 1980s and early 1990s. I don’t know what it is about them, but they just seem to have gotten it right. My mom has a fantastic E30 325i that is exceedingly well kept, and drives like a charm, about as close to a four-door Miata as one can get. The E30 sure has the sporty end of things licked.

You’d never guess this Mercedes could run on used veggie oil, would you?

Alas, there has always been a bit of a draw, at least to me, of the older diesel-powered Mercedes cars. Maybe it’s the ridiculous fuel economy, maybe it’s how they cruise on the highway so well, maybe it’s how they just absorb every bump in the road, quite the opposite of the Miata. Maybe it’s how quiet they are on the inside, maybe it’s how long overbuilt and low-revving diesel engines last. Then again, maybe it’s that, in terms of dollars and/or cents per mile, they can achieve infinite fuel economy via vegetable oil power.

The thing is, as the price of a gallon of gasoline has risen, so has the price of diesel-powered vehicles, compared to their gasoline-powered counterparts. So you have to do a LOT of driving to save any money. The number of companies selling veggie-oil conversion kits has also increased.

One day I was over at a local Miata guy’s shop staring at a popped motor, and another Miata guy (building a 302-powered Miata in the same shop) dropped by in a diesel Mercedes, silver with red leather. It was borrowed, but it was for sale. 1986 190D, 2.5L 5-cylinder non-turbo, automatic. And, it already had a veggie oil kit on it. At $1500 (a comparable kit is $1000 or so, and “only” 175,000 miles- nothing for a diesel like that.

It has some quirks and some issues- HVAC works, just not in the “traditional” way- it involves some manual switching to overcome busted controls- some rocker rust, this here, that there- typical 20+ year old car issues. To be expected, not the end of the world. But it’s got a veggie oil kit on it.

Did I mention that the car had a veggie oil kit on it? The kit on this particular car is a two-tank version. The diesel tank remains, and a 13-gallon veggie oil tank, with its own fuel pump, fuel filter and piping has been added in the trunk. Since veggie oil does not like to flow as well as diesel at low temperatures, there is a coolant line running from the radiator, zip tied to the fuel line, into the veggie oil tank, and then back to the radiator. The veggie oil filter is also electrically heated.

The veggie oil line attached to a coolant line.

In warm temperatures (say, 50-degrees plus) it’s no big deal to just fire it up on veggie oil. There is a switch on the dash to switch between the two tanks, as well as a secondary fuel gauge, although there are some issues with the senders failing in the veggie oil. If all else fails, there is a sight tube on the tank to visually check how much remains.

Secondary Fuel Gauge for Veggie Oil Level

When it is cold outside, the car must be fired and warmed up on diesel, and then switched to veggie oil. It does come up to temperature reasonably quickly when driven, but don’t expect it to do much if it’s just idling. Because of this, a two-tank conversion system will not save you very much in short trips in cold climates where it must be run on diesel a lot.

A single-tank conversion is somewhat more complex, but all around a better solution- the guy selling this car had recently completed a single-tank conversion on a newer Mercedes and was thus dumping the older one. A single-tank conversion relies upon hotter glow plugs that glow longer, different fuel injectors, and electrically heating the veggie oil to get it moving. These kits tend to be pricier, but I can completely understand why people opt for them- they are much better for how the average person uses a car- tooling around town.

It is important to note that we’re not talking about “biodiesel” here. “Biodiesel” is a refined product that can be substituted, one for one, with regular diesel fuel, no conversion required. Instead of investing in a conversion kit on the car, one can invest in the equipment to make biodiesel at home, a relatively straightforward process. The only thing in common is the starting point- used vegetable oil being discarded by restaurants- most have to pay to get rid of it, they’ll give it away for free. The hard part is picking it up and hauling it home to “refuel”- it can get heavy, fast.

What we are talking about is known in the industry as “straight vegetable oil,” (SVO) or, more specifically, “waste vegetable oil” (WVO). You just pick up the vegetable oil, run it through a filter to get rid of the bits of fries, chicken nuggets, fingers, whatever, and dump it into the tank. For easiest (and cleanest) refueling, the tank can (and should) be unbolted from the trunk and put on the ground- again, the biggest issue here is lifting it back into the trunk. I’m considering adding a secondary filler neck so that I can simply refuel the veggie oil as I would traditionally refuel a vehicle, albeit with a hand pump, since electric pumps can get pricey, fast.

The Veggie Oil Fuel Cell

Yes, the car does smell like McDonalds, the exhaust really does have a “French fry” smell to it. How does it run? Great. I actually think that the car runs more smoothly and quietly when on veggie oil rather than diesel- although this could be related to the fact that diesels run rough cold, and it’s run on veggie oil when warm and diesel when cold, I would still swear that the thing feels better on veggie oil than diesel, even when on diesel warm.

Now, this car sure isn’t for everyone. For starters, it’s slow. Really slow. That comes with the territory of a relatively heavy, non-turbo diesel sedan from the 1980s. It makes a 1.6L Miata feel faster than it should. The veggie oil system requires occasional tinkering, and since veggie oil tends not to be as clean as diesel, some periodic cleaning and more frequent fuel filter changes. In single-tank conversions, some of this can be mitigated by running some tanks of diesel through here and there to do some flushing.

So I’d highly recommend a single tank conversion to those who can afford it and use their car around town most of the time. However, for those with longer commutes or who will otherwise use the car for longer trips, the single-tank can save you some money. Remember, when in doubt, you can always call it a day and fill up with diesel, and you’ll still get some pretty good fuel economy. My dad compared this car on his commute to the other cars he drives (mostly a ’94 Suzuki Sidekick JLX and the 325i occasionally) and even with the higher price of diesel, the higher fuel economy puts the cost of commuting 15-20% lower than the other vehicles.

So it’s not a sporty car- if you want a sports sedan, opt for the BMW of the same vintage. It’s a rock-solid commuter car, though. And before you start complaining about parts prices- parts aren’t particularly expensive for this car. All of the accessories, body panels and the like are common across the 190-class line, which was far from a limited edition- they’re everywhere. The fact that the diesels sold well in Europe (and, to a lesser extent, here) means that poking around the internet finds you whatever part you need for a reasonable price.

While I don’t think the 2-tank conversion is an ideal solution, it’s more than good enough for my purposes, and I think it’s a fantastic bugger to have around, even if only ever run on diesel. There are a bunch of them out there with turbos and manual transmissions- these models are a bit sportier than the non-turbo automatic, but don’t expect wonders. I would be more than happy to chat anybody’s ear off about diesels and being powered by veggies- just let me know.