Modifying a Diesel Fuel System

In this section we will cover some basic vocabulary and techniques for modifying or converting a diesel.

Difference between Biodiesel and Straight Vegetable Oil(SVO):

Biodiesel – Biodiesel is basically refined vegetable oil.   Biodiesel has the consistency of regular diesel, requires little vehicle modification to use it.  Refining is typically done by combining WVO with methanol, lye, and heat in a distillation process.  Out comes Biodiesel and glycerin.    One of the drawbacks with biodiesel are that it is caustic, and will possibly eat away paint, rubber, hoses and seals as it passes through your fuel system.  Another issue is having to deal with chemicals in the refining process.  We like to say that Biodiesel is best for those more inclined to Chemistry, while SVO is more appealing to the mechanical folks.

How does an engine run on straight vegetable oil or SVO?  Well with biodiesel you refine the fuel, with SVO you refine the fuel system with heaters, pumps, hoses, filters etc.  Many like to call this a “conversion” but we like to say a fuel system modification.

Conversion – this is term commonly used for changing your fuel system around to accommodate WVO(Waste Vegetable Oil) or SVO(Straight Vegetable Oil).  WVO is also commonly called Veg, vegetable oil, oil, waste oil, garbage oil, grease, or liquid gold.

160 degrees F – This is the magic temperature which WVO will have a viscosity close to diesel.  It also happens to be the approximate temperature that your engine coolant is maintained at.

The ambient outside temp. isn’t close 160(yet) and WVO won’t flow well,  so a primary modification needed is the application of heat throughout the fuel system, from tank to engine, so that the oil will flow like diesel.  The oil doesn’t have to be 160 until just before it enters the engine/pumps/injectors.  Thus, you only need to apply enough heat is added for fuel to flow well.  Then, special focus and resources are spent on components that get the oil exactly to 160 right before entrance into the engine or engine components.

For instance, many people wrap the WVO fuel lines that run from the back to the front of the car with additional coolant lines.  This warms the fuel lines and WVO enough for flow.  The final and precise heating is done close to the engine with highly efficient heat exchangers.

Common components needed are:

Heaters or heat exchangers – This is what will do the primary heating of the vegetable to make it viscous enough for proper combustion in your engine.  Heat Exchangers are metal and heat up when the hot coolant flows through them.  This then heats the oil.   There are also electric(12v) heat exchangers and even some that use exhaust.

Filters – Separate or additional fuel filters for vegetable oil.  These protect your engine from water and anything that you miss during pre-filtering of your oil

Valves – These direct the fuel flow and allow you to switch the type of fuel being used and are controlled electronically

Pumps – Many vehicles will need a secondary fuel pump to move the WVO from the tank to the engine

Gauges – Gauges not only look cool but are important in monitoring coolant temp, fuel pressure or vacuum and the auxiliary fuel tank level. makes some nice gauges.

Tanks – These are needed to store the WVO fuel on the vehicle.  They typically have heat exchangers built in or added for better fuel flow.

Switches – These will not make your vehicle bounce and low-ride but will allow you to switch between diesel and WVO.

Good news: There are a variety of components out there, with many options for each vehicle.  It is nice to have a selection of solutions to choose from.  There are solutions for any budget and skill level, making fuel system mods. accesible and attractive to us all.

Bad news: There are a variety of components out there, with many options for each vehicle.  It can be confusing and befuddling to choose the right product.


Kits are a collection of components, which are just about enough to completely modify a fuel system.  The vendors will say they are complete, but many of them are missing important elements like mounting hardware or heat exchangers.  Be discerning when buying a kit.

Kits are a good solution if you can afford them and you don’t have the time or knowledge to assemble your own collection of parts.  One nice thing about purchasing a kit is that they usually come with tech. support.

Factors in purchasing a kit:

Budget – Kits range from $500 to $5000.  There are many factors which go into selecting a kit.  Cost is one of them.  Kits vary in terms of durability and quality along with functionality.

Cost of Car – It does not make sense to put a $2000 kit in a $1500 vehicle.  However, if you have significant investment in your vehicle, then it pays to have a quality kit that was designed for your vehicle.

Ease of installation – single tank kits are easier to install than dual tank kits

Ease of maintenance – Some kits allow for easy, quick and clean filter changes than others.

Installers nearby – Are there local installers for the kit you want or are they experienced enough to install it?

Check out this list of installers

Build and ship time – Kit vendors have widely ranging build and ship times.  One may give you a two month delivery date, while others can have it to you in 2 weeks.  It typically takes longer than the vender will tell you.  I recommend looking at customer feedback to get historical kit delivery data

To install or have installed:


Budget:  It can cost $500-$2000 to have a kit installed

Technical know-how:  You need not be a rocket scientist, but you it is best you’ve had experience working with your hands

  1. Ability to properly strip, split and crimp electrical wiring.
  2. Basic knowledge of plumbing.  You will need to plumb into your coolant and fuel lines.
  3. Have access to an array of tool like sockets, dremmel, cutting tools, drill etc.

…or…..Have a friend that can do all of this

300sd Conversion

I did my research and had ordered my single-tank WVO kit for my Navy blue 85 Mercedes 300SD.  The kit was said to have everything I would need.  I get the kit home and go to install the first part, the heated filter.  The filter’s mounting holes were drilled such that the filter would not mount properly.  For the next hour I diligently tried to get a hold of the Kit-Manufacturer.  No-answer then or for the next 3 days of installation.  I had to make many trips to the hardware store for tools and make-shift parts.  The vendor did apologize that he can’t be accessible at all times, but I would have been stuck without some basic carpentry, plumbing and electrical skills.  Point is, if you’re not used to working with cars and don’t have much patience, then have someone install the kit for you.

Basic Fuel System Modification types:

Single Tank –

Ahhh, the single tank!  Part of the glorious thought of never having to use diesel again. Well this can happen when you run on a single tank system.

Single tank means you use the stock fuel tank for the vegetable oil.  The conversion kits generally have less parts, are cheaper and simpler to install.  People generally run 100% WVO in a single tank when the in more temperate climates where the temperatures remain above freezing.  If you live in a colder climate, single tanks won’t work well.

With the Single tank kits, the car starts and initially runs on cold oil and cold oil is left in the engine.  It works, but the engine life is thought to be reduced because of running and sitting with the cold oil.  People generally use the early 80s Mercedes to run on single tank.

More Single tank info:


Dual Tank-

Dual tank means that you have a separate tank for vegetable oil, and use the stock tank for diesel in most cases.  Dual tank modifications have more parts, cost more and require more installation skill and time than single tak.  There is a switch that you use to change the type of fuel your vehicle is burning.  So, you would start the vehicle and stop on diesel, running WVO only once the vehicle and oil have reached the right temperature ~160

This is the way to go if you care about your car.

Here are some video examples:

Powerstroke Conversion

Duramax Conversion

Jetta conversion



Ahhh tanks.  There’s something alluring and particularly attractive to tanks.  I love tanks, especially heavy duty, shiny-silver aluminum tanks with nice welds, a built in heated pickup, a fuel sender and a drain.

*Heated Pickup – provides heat for a section of the tank where the fuel comes out


*Fuel Sender – This is a float or measuring device mounted in the tank that send the electrical information of the fuel level out to the fuel gauge.

Single tank- you generally use the stock fuel tank so you wouldn’t need to buy a tank.

Dual tank – You’ll likely need to buy a tank along with your kit.  The kit manufacturer will not necessarily have the tank that meets your needs.

Tanks used are generally made of stainless steel, aluminum and plastic.  There are tanks pre-made that are plug-and-play, and there are tanks that need to be converted themselves to run on WVO.  They need additional hardware like fuel-level senders and heating elements.  The kit vendors sell tanks that have all the appropriate hardware in them.  Otherwise you can buy boat tanks(plastic), or stainless steel tanks from places like Northern Tool and convert them to work with WVO.

I had my first WVO tank specially built.  I wanted it to fit under my cross tool-box in my truck bed, but be large enough to go without refueling for some time.  I made a 3D drawing, then faxed it to the fabricator who delivered!  This 40gallong tank is L shaped and is rock solid.  I paid $900 without shipping.

Here is the tank after 3 years of use.  It has ridden in the bed of my truck along with yard of compost, rocks, flagstone and gravel.  It even had grass growing on the top of it at one point.

Here’s how it looked in my truck:

Now I can show you a 20 gallon tank that was converted after it was made.  It is a plastic marine tank that was custom fitted with a home-made heated pickup, and a fuel sender.  The tank had no mounting brackets.  It’s in the back of a 1980 Mercedes 300D


More info:


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