Converting diesel Mercedes to run on grease

My son just bought a 92 Mercedes diesel that he intends to convert to run on grease. Like from fast food places. The car has about 100,000 miles on it and is in really great shape. He commutes about 180 miles a day and figures he can save a bundle on gas, because the grease is free. What are your thoughts about this? Has anyone ever done this? Is it really workable? Thanks

Geasels have their own loyal following…Don’t assume you will get the fry-oil for free. it needs to be processed before it can be used as diesel fuel. Sometimes there is a local Geasel nut with a back-yard refinery that has some extra grease to sell. I would do my homework before I embarked on this project…

Wow, we had an HHO generator question and now a grease-car question-- is gas going back up?

Flippancy aside, the grease-cars can be workable with some important caveats.

One, the statement “grease is free”-- be sure about this. In areas where grease cars got really popular there were enough people competing for used veggie oil that it started to get competitive and near the height of the high fuel prices, it wasn’t really cheap enough to justify the extra work of proccessing it. Even if you’re not in a high-grease demand area, it’s still not a matter of pulling up behind the Burger King and fillin’ her up-- you’ve got to have a pre-arranged grease connection.

Along these same lines, processing the grease yourself is almost inavoidably a huge mess (he doesn’t live at home does he?) and you end up with a lot of really dirty sludgy stuff you need to dispose of. In some places you can buy pre-processed veggie oil, but this usually ends up being about the same price as diesel.

Secondly, mechanically how workable it is depends on climate. The pour point of veggie oil is a lot higher than #2 diesel and so when it’s even a little brisk out, the veggie oil won’t flow through your fuel lines. If you live somewhere where it never, ever gets below 40 degrees or so, you can maybe get away with just running grease on a mostly unmodified car. But otherwise you need a second fuel tank with heat exchangers that you run coolant through. So you start the car on diesel and then when the engine warms up, it warms the veggie oil to point that it will flow. This adds a great deal of complexity to the project and plus if you’re somewhere cold, you end up burning a lot of diesel anyways (although with a 180 mile commute that might be less of an issue).

I know a lot of people who were really into the grease car thing a few years ago, but most of them have really come to the conclusion that it’s not worth the effort. Especially when you factor in that you have to drive around some ancient diesel car that’s expensive to run (a '92 Benz is not going to be cheap to run, grease or no), it really makes more economic sense to just find a newer fuel-efficient gas burner.

…figures he can save a bundle on gas.

He shouldn’t be spending ANY money on gas. This vehicle uses diesel fuel, not gas.

When you drive a diesel, you don’t stop for gas, you stop for fuel.

Now that we have the terminology down, if I had to harvest and refine my own fuel, and convert my car to run on the stuff, I would not have the time to do all the other important things in my life. I just don’t have that kind of time on my hands, and neither does someone who commutes 180 miles per day.

You can also use #2 fuel oil, but it may be illegal as you are not paying federal and state road taxes which are built into the cost of diesel fuel. What’s your time worth? Even if waste grease was free, you have to haul it home (truck, tank, pump, etc.), process it then put it in your car’s tank. Considering the time, effort and equipment necessary he may not be “saving a bundle” compared to filling at the station.


Collecting used fry-oil is an INDUSTRY. The people who put those collection tanks out behind restaurants PAY the restaurant owner for that product. Don’t assume you are going to get it free, or get it at all for that matter…

I Love The Way Those “Fast Food” Diesels Smell !

I was going into a Home Depot and a guy and chick were loading stuff into an idling Ford Diesel pick-up. When I walked by it the exhaust smelled like a Chinese restaurant. I asked what they were running and was told they collect used restaurant cooking oil that went in a tank in the truck’s bed.

I could never drive one. I’d be hungry all the time. I left Home Depot and went right to Burger King ( I don’t like Chinese food).


Buy the latest Car and Driver, they’re doing a conversion on a van. To do it right costs $$$. You need to add a separate tank for the vegetable oil, pumps, plumbing, etc. You start on regular diesel, then switch over for driving, then switch back before shutting off.

I think some folks confuse this with ‘biodiesel’, a 5% or more blend of regular diesel with diesel made from soybeans. Totally different.

I’m sure there are lots of ‘greaser’ forums out there, he’ll need to understand exactly what to do.

Far from ‘free’, though.

Someone who commutes 180 miles a day doesn’t have time for stuff like this…

Yeah, imagine having to round up that much old grease every week! And there’s nothing like the smell of old grease…

Grease burning aside, the 1992 Mercedes diesel engine is the 3.5 liter inline six that is famous for bending connecting rods. Google and read.

A 1985 or earlier five cylinder 3.0 liter 123 chassis 300D is a MUCH(for MikenNH) better choice.