Straight Veg Conversion

There are several ways to convert a diesel engine to run on straight vegetable oil (SVO). Most information on the Internet is reliable and this technology has been tested for nearly a decade now and many vehicle have run over 50k miles, perhaps even 100k. However none of this is tested at the level of a professional motor engineer, so make sure you cross reference everything.

The theory is that diesel engines simply run on oil and that they have been optimized to run on a particular oil as characterized by it’s viscocity and cetane number (CN) which is a quantitative value of how well it burns. Another important quality of oil is it’s energy density and has an effect the way a motor runs, mainly in the mileage efficiency. Vegetable oil is more viscous at ambient temperature and has lower CN, so in theory heat and a CN boost additive does the trick.

To boost the CN, a study was once reported on Journey to Forever that diesel fuel has a CN of 45 on average, vegetable oil has 40-50, and biodiesel has 45-65. Additionally, on the AMSoil CN boost additive it is noted diesel engines perform best with a fuel that has a cetane number greater than 50. So blending with a bunch of biodiesel or a few splashes of diesel fuel additive is required. I use Power Service Diesel Kleen as it boosts the CN the most – 8 points (AMSoil is also really good – 7 points).

There are 2 ways to heat the oil: electric boosters and coolant. Both means are usually taken advantage of. In colder climates, like here in Colorado, emphasis tends to be on the coolant requiring a complete warm up, while in SoCal the trend seems to be more electric centered. When it is very cold outside, I find my coolant only system is not enough and either an electric heater wrap or an in-line electric heater just before the filer is necessary.

More about viscocity can be found regarding how my SVO hybrid uses less petroleum than electric hybrids.

Theoretically it should work, but there are a couple things in practice to be aware of, the filter rating in particular. This summer I took my low-geared, 4-speed, 1982 Ford F250 on a road trip over a thousand miles through the desert with only an electric heater on the stock filter and could not get it to run on even 20% veggie / 80% diesel. It was 2x100W heaters and as you can see in the image below, they even slightly discolored the filter’s paint.

All we can figure is that the 6 micron filter was too tight for the WVO. I clogged 4 filters on the trip – this was the last one and it took the longest as the fuel was thinned to 20%$ WVO. I made this blend in my rear tank, changed the filter, looped the return, ran the truck for half an hour before switching. After 10 gallons of this blend (less than 200 miles), I could not even drive on the flat without blowing white exhaust and loosing power. Switching to straight petro diesel cleared it up.

A looped the return is accomplished by plumbing the return line into the source thus feeding warm fuel into the filter. In the image below the open valve accomplishes this. The valve shown as shut stops all the return from going to the tank. This killed the truck going downhill so it was only half cocked during the experiment described above.

Most coolant heated filter housings have filters rated for 10 microns, and the filters themselves are larger than the stock WIX 33811 on my truck.

Other issues to be aware of when converting a vehicle to run on SVO are manufacture dependent. The Chevy Duramax has never run well, the Dodge Cummins always has, but has external components that fail. Mercedes and Volkswagon made their injection system too precise. Here is a list of when these changes occurred:

1998 1/2: Dodge Cummins (temp sensor often fails)

2000: Mercedes-Benz (common rail injection)

2004: Volkswagon / Ford International (injection system)

2007: Dodge Cummins (expensive exhaust system clogs)