WVO 101: Waste Vegetable Oil Vehicle Basics

Our truck is a 1991 Ford F-250 that has been converted to run on waste vegetable oil (WVO). A WVO vehicle is also called a “grease car” and runs on used cooking oil from restaurants, which would otherwise be a waste product. We converted the truck because it has a smaller environmental impact than using a diesel or gasoline truck. Although we do still have to use a small amount of diesel, the WVO conversion gets us much closer to our goal of being fossil-free.


What is waste vegetable oil?

Waste vegetable oil is the oil from restaurant fryers that has been discarded.

How do we find WVO?

We ask restaurants if we can take their discarded fryer/cooking oil. Majority of the time restaurants already have a contract with a biodiesel company to have their waste vegetable oil picked up. While this isn’t great news for us, because it means we aren’t allowed to get the used oil, it’s great to see that this waste product is being converted to something useful rather than being thrown away. Getting WVO isn’t as easy as we thought it would be because of the above-mentioned contracts. If we were living in one place then we could build a relationship with a restaurant or two, but being on the move we are always starting the conversation over.

How do we physically get the WVO?

 Sometimes restaurants pour their used oil back into the 4.5-gallon plastic containers (referred to as cubies) that the oil originally came in. With those we just take the cubies with us. For oil that’s been discarded into barrels, we use an electric pump. The pump is powered by the truck’s batteries and has two hoses connected to it. We insert one hose into an oil drum to collect the WVO and the other hose fills up an empty container with the collected grease.


How is the collected WVO stored?

Pre-filtered oil is usually collected into reused cubies, and sometimes 5-gallon plastic buckets.


It's very rare for us to get this much WVO at one time.


Can the WVO be used straight from the restaurant?

WVO has to be filtered first to remove any bits of food.  The truck’s engine requires fuel with no particles larger than 10 microns in it or else it will be damaged. We did add a fuel filter in the truck for the WVO, but its job is only to protect the engine in case something makes it past our pre-filtering. If we relied on that filter to clean the raw WVO it would clog up in a couple minutes.

Where do we filter the WVO?

Initially we filtered the WVO we collected in the restaurant parking lot. But we don’t filter on-site anymore because filtering is time-consuming and messy. We now bring the unfiltered grease back to the RV and filter it there.


We're not usually this messy but our solar charge controller had to be switched out.


How do we filter WVO?

The contaminants in used oil vary in size from source to source, and if you find high quality oil, there will be much less to filter out.  It’s best to use multiple stages of filters, because if you ran all the oil through just the finest filter, it would clog right away. We use tall sock filters that varies from 75-micron down to 1-micron to filter the grease. The sock filters sit in one another and are placed in a 5-gallon bucket with the bottom cut out. Underneath that bucket is another 5-gallon bucket that catches the filtered oil. We pour the filtered oil into the WVO tank that sits in the bed of the truck.


This is our collection (left) and filter system. 


Is WVO free?


Does that mean we don't spend any money on fuel?

Yes and no. Yes because we don’t pay for the WVO that we collect. No because we use a variety of materials to filter the WVO and maintain the truck.  Sometimes we eat at the restaurants we get grease from as a thank you. And there’s still a need for diesel (next question explains why).

Why is diesel still used in a WVO vehicle?

WVO can only work in a diesel vehicle after it’s been heated up and its viscosity has been thinned to a consistency like diesel. So diesel is used to start our truck and warm it up so the coolant (which is hot after it goes through the engine) can be used to heat the WVO.  For us, this takes between ½ mile and 5 miles of driving, depending on how hard the truck is working (uphill, towing, etc.).  Diesel needs to be run through all the WVO lines in the engine before the car is turned off so the WVO doesn’t coagulate the lines and filter (especially in cool weather). Diesel also needs to be left in the fuel lines closest to the engine so it’s ready to be used for the next start-up.

Why don't we convert WVO to biodiesel?

To convert WVO to biodiesel requires equipment, chemicals ($), and precision. Living on the road with a limited amount of space makes it hard for us to carry chemicals and the necessary equipment (our filtering setup is pretty compact).  Also, we would still have to filter the WVO first before making it into biodiesel. Also, the biodiesel-making process takes longer than simply filtering WVO, which makes it harder to do while mobile.

How does a diesel vehicle burn WVO?

A diesel engine is created to burn fuel that has a low flash point (the temperature at which it can be ignited in air) unlike a gasoline engine. Fuel that has a low flash point, like diesel, is considered a “fuel oil”. Gasoline is much more volatile: If you pour out diesel on the ground and try to light it, it doesn’t burn. Gasoline, however, will. WVO is similar to diesel in the sense that it also has a low flash point. A diesel engine can use “fuel oils” because it creates more compression in the cylinders than a gasoline engine. It also runs its fuel through a high-pressure injection pump, which sprays the fuel into each cylinder in a fine mist. The fine mist mixes with air and in combination with the high pressure in the cylinder, combustion occurs. Here's a cool animation that explains how a diesel engine works.

Unheated WVO is much thicker than diesel, so if it goes through the injectors, it won’t make a good mist (imagine pumping ketchup through a lawn sprinkler). It will still burn, but not completely. That leaves a bunch of junk behind inside the cylinder, which can eventually (or rapidly, if it’s really bad) completely ruin the engine.

There are numerous ways to heat WVO for use in a diesel engine. It’s still very much a matter of personal opinion which one is “best”. We use only hot engine coolant to warm the oil (as do many setups), but some use electric heaters to help. The heating starts at the hose where the oil is drawn out of the tank (but we don’t heat the whole tank).  Oil then moves through hoses to the engine compartment, where it passes through a heated filter (the safety filter), then the pump which is pulling it.  Next, it goes through a heat exchanger where it gets a final burst of heat, before heading to the diesel injection pump. A pair of remote-activated valves handles the switching between diesel and WVO.  We use a Greasecar.com “Co-Pilot” computer to monitor the temperatures and control the valves, but that could be done with manual switches and gauges instead.

What the conversion looks like under the hood.

What mileage does the truck get running on WVO?

Our truck gets 11 mpg on WVO just like it does on diesel (and the same mpg whether or not we’re towing the RV).

Does the WVO exhaust smell like French fries?

Our WVO exhaust doesn’t smell like fries because we get most of our used oil from Asian restaurants. I think it smells like food while Jerud things it just smells like a grease fire.

Can any vehicle run off WVO?

Only diesel vehicles can run off WVO. Some are better suited than others, because of the type of engine (newer ones are a bit more tricky), or just the available space under the hood. Older trucks, vans, and buses tend to be the easiest. Mercedes and VW passenger cars are also popular choices.

Can any WVO be used?

Essentially yes. The type of oil it is doesn’t affect anything (ex: whether it’s sunflower oil or soybean oil). But the quality of the used oil varies from restaurant to restaurant. Used oil from Asian restaurants is typically cleaner than other restaurants because of the type of breading used. There is usually much less crud in used Asian oil. Some discarded oil has water mixed in, either because of how the fryer is cleaned or the restaurant just doesn’t fully close the lid on their oil drums, allowing rain into the containers. Water is extremely harmful to an engine if left in the fuel, but can’t be effectively filtered.  It can be separated by settling, but that requires keeping it still for at least a week – not practical for us.

Can filtered oil be poured directly into a diesel vehicle’s fuel tanks?

Yes, filtered WVO can be pour into a car’s gas tank. But once the fuel tank has had WVO in it, that tank shouldn’t be used for diesel unless it’s cleaned out first.

How large is your WVO tank?

Our WVO tank that holds the filtered grease is 37 gallons.


Pouring filtered WVO into the WVO tank.


How much did the conversion cost?

Our conversion cost us around $2,700. We could have spent less on the conversion. But we overspent in some areas because we were in a hurry and this was our first conversion. The Greasecar computer is a luxury item that we could have skipped. Knowing what we know now, we think we can do it under $2,000. More on this in another post. 

How much does it cost to maintain a WVO vehicle?

We have about 7,000 miles on the truck using WVO and we're still on our second set of sock filters. The two sets of sock filters cost us about $24. We've replaced the truck fuel filter once and they are $27 each. But we've paid for two filters (one that's been used and the other that is currently in the truck) so that's $54 total. So far we've spent $78 in 7,000 miles which comes out to $0.01 per mile. But in reality that's the cost if everything went right with using the WVO system, which it hasn't (more on that in a different post). There is also the cost of the collection equipment that isn't included in here, but we're still experimenting with that so we don't have a final cost yet.


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