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Benz Veggie Conversion: The Nuts and Bolts


With the domestic auto industry collapsing around us (and keeping bloggers typing away madly), I've had little time to report on the host of mechanical changes I've been making to the 1982 Mercedes 300TD Wagon I'll be driving to L.A. in December. I've been underneath the oily old diesel every weekend making mechanical updates and preparing for my cross-country trek.

First up were fixes to get the 330,000-mile stalwart wagon operating at its best before setting sail from Atlanta to Los Angeles. Tightening the steering box eliminated most of the steering play and made the car much more pleasant on the highway. Replacing one of the rear struts on the self-leveling suspension eliminated a loud clunking from the right rear (and ensured proper self-leveling operation). And removing the dash, replacing the heater core, rewiring the HVAC controls, and ensuring proper vacuum to the entire system (and then putting it all back together--ugh) gave me heat and ventilation for the first time since buying the car in 2006.

Making the car run on used vegetable oil is remarkably simple. Pictured and described below are the six main mechanical items needed to turn my ride from a petroleum-fueled vehicle into one that will run on waste vegetable oil (WVO), biodiesel, or traditional diesel fuel.

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Colin Veg Conversion #4

Colin Veg Conversion #4

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#1) 16-plate brazed copper heat exchanger. Vegetable oil only needs to be heated to be burned in a diesel engine. It is too viscous at room temperature to be properly vaporized by the injectors, so heating it to about 180 degrees Fahrenheit does the trick to make it thin enough for proper burning in the engine. The unit above takes hot coolant from the Benz's radiator, cycles it through a metal matrix of tiny passageways, and returns the coolant to the radiator. Pressed right next to the hot coolant passages is another matrix of passageways, these with vegetable oil flowing through. Heat is transferred from coolant to vegetable oil, heating it quickly and preparing it for duty as fuel for the turbodiesel inline five.

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Colin Veg Conversion #6

Colin Veg Conversion #6

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#2) Heat Exchanger + Fuel Filter. Right before feeding it to the engine's injection pump, it is wise to heat the vegetable oil once more to ensure full atomization in the combustion chambers. Additionally, filtering the oil again ensures that no impurities enter the engine. The unit above functions similarly to the 16-plate heat exchanger above (#1), but features a smaller heat exchanger and a large-capacity, 4-micron oil filter that filters any impurities out of the oil. Engine coolant from the radiator is again used in the lower metallic chamber, and vegetable oil enters and departs at the base of the unit through the two copper fittings. After passing through this unit, the waste vegetable oil is ready for combustion.

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Colin Veg Conversion #5

Colin Veg Conversion #5

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#3) Fuel and Coolant Hose. To route vegetable oil from the gas tank, through both heat exchangers, and on to the injection pump, a 3/8-inch fuel hose (smaller spool in the middle) is used along with hose clamps to ensure the system is sealed. All coolant to and from both heat exchangers is routed through 5/8-inch coolant hoses (the larger hose on the outside).

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Colin Veg Conversion #1

Colin Veg Conversion #1

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#4) Continuous Duty Solenoid. A purge tank system is used so that the engine may be started and shut down on diesel or biodiesel. As the radiator is not hot upon startup, diesel or biodiesel must be used on a cold start until the radiator is sufficiently warm enough to heat the vegetable oil through the heat exchangers. This solenoid is triggered by a dashboard switch operated by the driver. When the switch is flipped on, the solenoid sends power to two fuel switchover valves that route fuel from the main fuel tank where the waste vegetable oil is stored. When the switch is turned off, the valves route fuel instead from a purge tank that has approximately two gallons of diesel fuel or biodiesel.

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Comments (7)
  1. With gas below $1.50 in several states already, I'm sure many will go thru that lengthy nightmare to convert their Mercedeses into an insect-infested truly grease-monkey!
    NOT!
     
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  2. Yeah, perhaps not Ed, but $0.00 per gallon still beats $1.50 in my book. And it's only a lengthy nightmare to the non-mechanically-inclined. It's a fun saturday project for a die-hard car communist like myself ;-)
     
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  3. I haven't seen diesel for $1.50 anywhere (and I'm sure I never will), so it's time to kick the habit before that stuff eats through your brain, Eddie...
    Great project btw. Will you be begging Taco Bells to spare you some oil in the middle of nowhere or are you taking a big drum full of vegetable oil with you?
     
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  4. thanks JKD - actually, I just got a donation of 90 gallons of waste vegetable oil from a local greasy spoon. That should get me about 2,500 miles by my calculator, and yes I'll be toting it all in the back of the wagon in plastic drums. The load-leveling hydraulic suspension shrugs off the extra weight, about 650 pounds. I'd rather get my oil across the country as I think it's a better story, but restaurant owners give you a pretty weird look when you ask them for their old oil...why, do you know any restaurateurs on old US-80?
     
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  5. It makes sense to take it with you. I recall a similar drive/project where a guy converted his RAM and had drums and drums of this stuff sitting in the back of the pickup.
    Would you call this "biodiesel"? It is/was huge in Germany for many years but they're departing from it and reducing the amount of it in regular diesel now since it does have negative long-term effects in newer cars but your Benz will just eat this stuff up with gusto I'm sure.
    650 lbs. sounds like Ed's mother-in-law, so the weight is not going to be a problem :-)
    Can you put regular diesel in case of emergency on the fly if needed?
     
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  6. I wrote, CLEARLY,
    "With gas (NOT DIESEL!!!!!!!!!) below $1.50 in several states already, "
    And I was 100.00% CORRECT,, and you can prove it for yourselves on GASPRICE WATCH.COM, RIGHT HAND TOP CORNER, NATION-WIDE Minimum gas price was $1.47 and FALLING in INDEPENDENCE MO, when I CORRECTLY wrote my piece.
    But you can COUNT on a 100%, USDA choice moron like JERKD to not understand it.
    Colin, give the idiot some more kudos.... they may help him obtain some self-esteem.
    And what is that about a grease monkey being a... communist, Colin? HELLO????
     
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  7. Ed - I believe you may not be accordsforall after all - you're much dumber than that guy though I could have sworn he hit the bottom :-)
    Let's analyze your comment:
    "With gas below $1.50 in several states already, I’m sure many will go thru that lengthy nightmare to convert their Mercedeses into an insect-infested truly grease-monkey!
    NOT!"
    A person has an old Merc diesel (or any diesel) and wants to save money (or save the planet) by converting it the way Colin did... Then they see the prices of gas dropping down to buck fifty and reconsider??? How's that for a reasoning of a two-year old? Has the acid done that much damage already?
    Get back on the topic or get lost. Hi-jacking every thread with your pro-Honda or anti-domestic or anti-anything comments needs to get you kicked out, foo'
     
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