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How to make your own fuelHow to make a simple heat exchanger
How can I know if my engine will run on Straight Vegetable Oil?If my engine runs on SVO, then can I burn WVO?

Can I burn straight vegetable fat in my diesel engine?
(This is quite a large page and may take several minutes to download)

Yes you can,  BUT you have to modify the fuel slightly, or modify the fuel system in the vehicle to heat the vegetable oil before it reaches the injector pump.  Some engines adapt more easily than others. Some engines seem to run on straight vegetable oil without any need for adaptation at all, for example Mercedes 123 and 124 series.

My VW Passat 1,600 Turbo Estate ran on SVO and on Modified Used Vegetable Oil (MUVO) without any problems.   I have also used MUVO in our Renault Traffic van, and in a VW Golf and VW 1.9 Transporter van, and in our Mercedes123 series estate.  I have about 100 local customers who I supply with MUVO fuel.

It may be that VW engines generally are more tolerant to vegetable oils, and I have been exceptionally lucky to have the VW Passat.  (I also happen to like this very economical vehicle, but other people may consider it under powered by to-days standards).  But, it did splutter when I fed it with waste vegetable oil which was contained a lot of animal fats.  The stearine fats (lard) clogged the standard fuel filter, and starved the engine of fuel.  However this did not damage the engine itself.  Cleaning out the fuel delivery pipe from the tank to the engine had to be achieved by pumping with hot kerosene - not the safest task!

our 'A' reg, VW Passat 1600 turbo estate
did over 210,000 miles, and was still going strong!
(I then blew the head gasket when driving it hard on super power bio-fuel,
and we took the head of to find it was perfectly clean)

Mercedes engines are probably the best at running on straight vegetable oil, and I know of a taxi driver in Germany who has been running his unmodified Mercedes on unmodified straight vegetable oil for a long time.  I have also run our Mercedes 123 series on duck dripping which being semi-solid, does not attract Excise Duty in the UK.    In Germany there is no Excise Duty on any non-mineral oils used as a road fuel, other than VAT.  Other engines may be equally accepting of unmodified vegetable oil.  It is a matter of trying it, initially in a way that anticipates and minimises the risks.

What problems may I encounter?

There are several potential problems:
     1). The fat will not flow through the fuel supply pipes
     2). The fat clogs in the fuel filter
     3). The fat forms an emulsion in the return pipe
     4). The fat will not burn effectively
     5). The engine will not want to start on the fuel from cold

All of these problems can be overcome.  You can do this by modifying the vehicle fuel supply, or modifying the engine itself or by modifying the fuel.  Increasingly, I find the best solution is often a combination of all three.

MODIFYING THE FUEL SUPPLY

Lets look at each problem in a bit more detail....

1). The fat will not flow through the fuel supply pipes
Vegetable oil is considerably thicker (more viscid) than mineral diesel.  The fuel pipes running from the tank at the rear of the vehicle to the fuel filter and the engine are quite narrow.  When the temperature drops vegetable fat gets much thicker.  At normal summer temperatures rape seed oil is thin enough to flow through standard fuel pies, but in winter conditions it turns into a jelly, and the injector pump will not be able to suck it through the pipes from the tank.  This also happens when using Derv, and some lorry drivers put a small amount of petrol into their diesel when conditions are exceptionally cold to reduce the risk of fuel supply starvation.  However, petrol is an Octane fuel that requires to be ignited by a flame, so adding petrol to diesel will reduce the Cetane value.  Therefore petrol should only be added to diesel in very small amounts if the weather is very cold as a way to reduce jelling.  One litre petrol to 500 litres Derv is probably sufficient.

If you suspect problems with blockage in the fuel supply pipes then look for little bubbles of air in the transparent sections of the fuel pipe connecting the fuel filter to the injector pump.  The occurrence of these little bubbles may suggest that the effort needed to suck up the jelly-like fuel is creating air bubbles in the pipes.  The effort required to suck a thick fuel through the narrow fuel delivery pipes and through the fuel filter places an extra strain upon the injector pump that it is not designed for, and it also wastes energy.

There are four possible cures:
   a).   modify the fuel
   b).   replace the pipes with wider pipes
   c).   fit a new form of connecting pipe with a smaller pipe inside a larger pipe so the hot return oil helps to warm up the flow pipe
   d).   fit a small heater in the fuel tank
   e).   fit an additional pressure sensitive fuel delivery pump (for example from an old Mini)

I have not experienced this problem myself on a vehicle, but I have tried all of these solutions where big engines have been converted to run on semi-sold fats to generate electricity.  For my own vehicles I prefer to modify the vegetable oil, and this is explained at the end of this section.

2). The vegetable oil clogs in the fuel filter
This is the only problem I have ever experienced, and I was really asking for it by trying to burn waste vegetable oil that had a high contamination by animal fats.  This fat smelled of vomit, was totally opaque, and was unpleasant in every other way (be warned!).  I had removed surplus water and filtered the fat when heated, but heating animal fats even slightly will enable them to pass through a filter.  But once in the car tank the remaining animal fats will start to solidify and will then collect together in globules.  These fatty lumps can be seen as a crusty surface on the inside of the fuel tank, and they may block the fuel supply pipes. They will most certainly collect in any standard un-heated fuel filter and eventually form a solid lump of gray white lard.  When I experienced this problem I changed the filter and the car immediately ran normally.  So I then opened up the old filter with a hacksaw, and found it to be blocked solid with lard.  I put the whole filter on a tray in the oven, and the lard melted immediately, and the kitchen smelled quite bad too!

The cure is to fit a heated fuel filter.  Excellent water heated fuel filters are fitted as standard on Peugeot cars, and a visit to a scrap merchant should find you one for £15.00.  Old ones are in three sections, the upper block contains the fuel connections, a hand operated priming pump, and a mounting. The middle section is the filter itself (they cost about half the price of normal canister type filters), and the lower section is the water heater.  You will have to strip the unit and remove the internal thermostat inside the water circuit.  It is also worth cleaning out the messy gunge left by the former engine's coolant water.  I fit a Peugeot heated fuel filter on to the bulkhead next to the standard fuel filter, and I connect the water into the water pipes that provide immediate heat to the car interior, using normal 15mm copper 'Yorkshire' plumbing connections, and jubilee clips.  Always carry at least one spare filter cartridge in any vehicle used for fuel experiments, and the tools needed to exchange them.

More modern Peugeot fuel filters are still water heated but they are designed into the pipe that takes the coolant water from the engine to the radiator.  These can equally well be used as a fuel heating system.

3). The fat forms an emulsion in the return pipe
When the fuel is compressed by the injector pump, not all the fuel escapes past the injector nozzle into the engine cylinders.  Most of the fuel returns along the jumper pipes and is then pumped back to the fuel tank.  This helps to warm up the fuel in the fuel tank slightly which also helps to overcome problem 1).  However, when any liquid is compressed and then decompressed it forms little bubbles (just like when you shake a coke bottle and then open it quickly, it squirts every where with foaming sticky liquid).  Well, the same happens with vegetable oil fuel, but the bubbles are much smaller.  If the fuel is at all gloopy these bubbles do not disperse so quickly, and the fuel looks like dirty milk.  This bubble filled return fuel is much lighter than normal fuel so it does not mix in the fuel tank but instead floats on the top of the fuel.   This does have the advantage that it will help to dissolve any fatty surface on the inside of the fuel tank, but it does not mix well with the fuel in the tank, and can form a solid layer.  This can become a problem if the tank is less than 1/4 full, but I have not experienced the problem myself (yet).  It is a problem that has been reported to me by others.

There are possible cures...
   a).   keep the fuel tank more than 1/4 full especially in colder conditions,
   b).   return the white return fuel to the fuel supply to the injector pump.  This problem is only noticed when starting, and after about 10 minutes of running all the pipes should be so warm that the bubbles disperse almost immediately,
   c)    provide a small electric heater to the fuel tank.

4). The fat will not burn effectively
This may be noticed by excessive carbon in the exhaust, smoking, more than normal, or poor combustion or loss of power.  It can be a sign that the fuel is causing the injector nozzles to clog and this is distorting the spray pattern.  If you experience this sort of problem then there are several possible cures...

a).  Heat the fuel.
This can be done with a simple heat exchanger made from 28mm copper pipe inserted into the hot water pipe that connects the engine to the radiator.  This pipe can have a 90 degree bend fitted at each end to help with the alignment.  Around this pipe is wound a coil of 8mm micro-bore central heating pipe.  I find eight to ten turns are adequate.  Fill the pipe with dry sieved salt before bending it or it will collapse and make an impossible mess.  Water or oil can also be used but it must then be maintained under pressure.

I strap the two ends of the micro-bore pipe with wire and run flux and solder over the whole thing to join the two pipes together thermally.  Shake out as much of the salt as you can and blow out the remaining salt with an air line taking care not to get any salt dust in your eyes!  Dissolve any left behind with with hot water.  This task takes longer than the actual bending and soldering. 

The heat exchanger can be fitted into the water pipe using jubilee clips, and the fuel pipe fitted to the 8mm micro-bore pipe with rubber sleeves. The flow of the fuel is contrary to the flow of the hot water.  The whole unit can them be wrapped within the thickest form of pipe wrap insulation, and secured with cable ties.  This will ensure the fat is hot enough to burn in almost all conditions.  I have included some pictures of such a unit in my Passat Diesel but as I said before it will also run without it.  This is the first heat exchanger I ever made, and it has more turns than are necessary.

click to enlarge

b).  Fit different injectors
Standard injectors produce a jet likened to that produced by a water pistol.  But injectors can also be bought that provide an atomized jet likened to the mist produced by a laundry or garden spray.  This atomized jet facilitates better burning of fuel, and also makes the engine run more smoothly.  The exact type of nozzle required will have to be bought from a specialist dealer like LS(uk), or Dieselsend.de in Germany.  They are generally called 12 degree jet  nozzles.   I was able to get the necessary pieces from my local LS(uk) dealer, and they came within a few days.  The dealer then fitted the new nozzles, and at the same time calibrated the injectors themselves.  This made a huge improvement in performance - even when using fossil fuels, and it made me think why is this sort of nozzle not fitted as standard in all engines?

c).  Increase the Cetane value of the fuel.
This can be done by adding a proprietary fuel additive like Miller's Diesel power plus, which has an extra Cetane boost.  Easy Start Di-ethyl ether can also be sprayed into a small sample of fuel to see if this improives running. This technique can be sued to find out if the enegine will run better with an increase in cetane value, and if this cures the problem then it is likely that fitting a heat exchanger will also solve the problem.

d).  Change the timing / injection pressure
I have not done this, so I cannot speak from personal experience.  The timing on a diesel engine is not quite the same as that on a petrol engine.  The timing on most diesels is never altered, and often it is not set correctly.  Petrol enegines are quite critical of the timing precision, and will fail to run if it is not withjin quite narrow margins.  However, diesel engines are so rugged they always seem to work if they are not set up optimally.  Slightly retarding the injection time means that the injection takes place when the pressure of the air inside the cylinders is higher.  This makes for better ignition, but there is a slight loss of power.  Its a matter of swings and round-a-bouts.  Similarly increasing the injector pressure also has the effect of retarding the timing, as the cylinder pressure has to build up more before the fuel is injected.  This pressure can be increased by ten bar by inserting a one thou spacer under the spring inside the injector.

Modern electronic injection technology does not provide this mechanical means of adjustment.  Instead it is necessary to reprogram the chip in the electronic control box.  If you have experience in making these modifications then please let me know.

Bio-power has also deeveloped a self-regulating electric fuel heater.  This is mainly used in Ford and Vauxhall engines that are nmore reluctant to start when cold.  We will soon be able to provide a kit for the conversion of most engines to burn straight vegetable oil without the need to provide a second fuel tank.

MODIFYING THE FUEL

So far I have explained how to solve the problems by modifying the fuel supply system within the vehicle.  However, my view is that most if not all of these problems can be overcome by modifying the fuel itself.  The vegetable oil suitable for this can be collected from most catering establishments that use vegetable oil for cooking chips.  The oil must be in a liquid form, and not the solid pasty type of fat generally used in traditional British Fish & Chip shops which is made from Palm oil.  New oil sold at a grocers shop or supermarket can be used but it does not make such a good fuel, and using food grade oil simply puts up the price of an essential commodity.  I strongly recomend that you find a local supply of used runny vegetable oil if you seek an economicaly viable 'green fuel' solution. 

I call this form of fuel MUVO (Modified Used Vegetable Oil).  I do not recommend the use of oil that has been heavily contaminated by animal fats. Reject any oil that smells of vomit as it will contain water which has become septic.  The used vegetable fat should be translucent, and runny, with an amber or light brown colour.  I allow the collected oil to settle in a 200 litre drum for about 2 weeks before processing. 

The settled oil can be prepared for use firstly by heating to about 60 degrees C so that any water will form droplets at the bottom which can be removed, and the oil is then filtered to remove burnt chip pieces, and any other form of debris.  I use a 'Jay Cloth' supported in a stainless steel sieve to filter the warmed oil.  The felted floor cleaning cloths sold in Lidl folded double are also excellent, and can be used many times.

The feul we make for commercial sale has water added, so why am I suggesting you dry the oil before use as a fuel?  The answer is that beginners should work with dry oil before learning how to work with water in their fuel.  This technology is dealt with in our Bio-power Seminars.

The simple modification then consists of adding a natural solvent to the fat in the proportion ranging from 10% to 30% by volume.  I find 10% to 20% adequate in North Wales, the larger proportion being in the colder months.  This solvent serves two purposes.  Firstly it thins the fat making it less likely to clog in the fuel supply pipes, and secondly it acts as a detonator or Cetane improver by exploding slightly quicker than the raw vegetable oil.

Many different materials can be used as a solvent, and they have various advantages and disadvantages...

There are many other materials that can be added to the fuel to improve the performance and keep your injectors clean including water (but not simply poured into the oil).  Proprietory fuel improvers like Reddex Diesel Additive, Stanadyne diesel additive and Miller's Diesel Power plus, provide many of these materials that are expected as liquid engineering by modern diesel engines.  These proprietary additives and others can be found in a local motor accessory shop, and must be used as instructed in very low proportions - as little as one part in one thousand parts. 

The addition of solvent can also facilitate the further settlement of the stearine fats.  It may take some time, but if modified fuel is allowed to stand and is then examined it will be noticed that the top levels are clear and bright, but the bottom is white and opaque.  If you are careful when pouring the vegetable fat into your vehicle then you can prevent this precipitated white fat from being used.  A better technique is to store the fat plus solvent for about 6 weeks then rack it off like racking a wine or beer must for bottling with a plastic siphon tube.  A second filtering after about 6 weeks of sedimentation at room temperature may be adequate to improve the fuel considerably.  The finished fuel should be perfectly translucent like a good beer or whiskey - with no trace of a sediment!

Before using this fuel I strongly suggest you fit a clear plastic in-line fuel filter in advance of your normal fuel filter.  These can be obtained from your local motor accessory shop.  This filter will monitor the quality of your fuel making, and it will trap any remaining animal fats or suspended crystalline fats that would otherwise block up in your fuel filter - causing fuel starvation.  Because this filter is translucent you can easily see what sort of gunge if any accumulates.  Replacing the translucent filter costs about £1 to £2,  but the normal filter in a steel container will cost many times that amount and you can't see what is happening inside.

I also suggest you buy a can of 'Easy Start' di-ethyl ether, (a form of alcohol) that can be squirted into the air intake port only if your engine is reluctant to start on a cold morning.  Once the engine is started you will find it will run all day.  The trick in using Easy Start or any other form of gas like Butane or Camping Gaz, is to use as little as possible. 

If experimenting with home made bio-fuels then you should also ensure you have a good battery and good battery connections.  Also, check you oil levels regularly and watch out for any increase in oil level which could suggest that vegetable oil is getting past the piston rings and into the sump.  Mixing vegetable oil into hot mineral engine oil can cause polymerization, and this will turn your engine oil into a gum.  It is then no longer able to provide the necessary lubrication and this can lead to engine ceasing.  If you suspect your engine oil is sticky then add an oil cleaning agent and allow the engine to run for 15 to 20 minutes to circulate the oil adequately and then allow the old oil to drain out and fill with new oil.  Miller's Oils (Brighouse, Yorkshire) provide an excellent free service of testing you old engine oil and they will report if you should have changed your oil earlier.

Words of warning

If, having read this section you are minded to try burning straight vegetable oil, then some words of warning will not be out of place:

Firstly, I do not accept any form of responsibility for any damage you may do or problems you may encounter.  I have published this section in good faith to disclose what I have learned having now run many types of engines on simple blended bio-fuels without any problems over a period of more than 6 years.

The best engines in terms of bio-fuel tollerance are Mercedes, BMW, VW, Renault long stroke engines, Peugeot, and the Japanese makes.  I have never had any difficulty working with engines with CAV Lucas injector pumps as opposed to Bosch Pumps.  It is often reported that CAV Lucas pumps are not strong enough to run with straight vegetable oil.  This is not my experience, but I am careful, and also I live very near the sea in North Wales, so we do not have extreme frosts.

If you are tempted to experiment, bear in mind that currently you must register with HM Revenue and Customs as a maker of bio-fuels, and you must provide the necessary returns for the tax due of the fuel you burn in your vehicle on a monthly basis.  This is fully explained elsewhere in this web site.  However, it is likely that the requirement to register with HM Revenue and Customs will be dropped very soon if you intend to make fuel on a small scale or for your own use. 

Finally, if you do try it out, then initially do it this way.....

Buy a new 3 litre bottle of rape seed oil, and secure it in a convenient place within the engine compartment.  Start your engine on normal diesel and let it run until it is well warmed.  Carefully remove the hard plastic fuel supply and return pipes from the rubber sections nearest to the fuel filter, and insert new sections of similar form of fuel supply pipe about 18" to 24" long.  Insert these into the top of your vegetable oil bottle, so the supply pipe reaches to the bottom and the return pipe discharges at the top.

Restart the engine in the normal way.  It may run for a time and then suck any air pockets through the injector pump.  You may see the bubbles in the transparent sections of the fuel supply pipe.  Let the engine run for a while whilst stationary.  Do not drive on the road.

Listen to the engine sound.  It should be less rattly and generally quieter than when running on Derv.  You will smell a different odor from the exhaust.  (This will become a smell you will come to love!). Try revving the engine to assess its performance.  My guess is that you will not notice any significant difference. You may see a white or yellow scum forming at the top of the rape oil bottle, and it may overflow slightly if the bottle is completely full.  This shows that the volume of the return fuel is greater than the volume drawn by the supply pipe.  The engine does not make additional fuel, it is caused by the little bubbles.  As the fuel in the bottle gets warmer, so this white cloudy mass will disperse.  This is normal.

Testing a new fuel,
the floating cloudy layer of return fuel is normal when starting.

If you are encouraged by this experiment, then get registered as a self assessing Tax Collector, and start putting the clean vegetable oil into your normal diesel tank.  (Don't forget to put all the pipes back!).  Do not burn 100% vegetable oil immediately, try say 60% derv and 40% vegetable oil, then 50% / 50%, then as you get closer to 100%.  Start by adding about 20% solvent to collected used vegetable oil.  I also suggest that you keep reverting back to normal Derv every few months. You will probably notice the Derv makes a lot more engine noise, and you may also find the vegetable oil is a much better top of cylinder lubricant than Ultra Low Sulphur Diesel.

Check you engine oil levels especially carefully, and also check the tips of the injectors for any sign of carbonization or clogging.  Watch the exhaust pipe for excessive fumes or smoke when the engine is warmed up.  All cold diesel engines smoke a bit on start-up.

Please let me have a report on your success.  We need to know which diesel engines work well on straight vegetable oil.  

How can I know if my engine will run on Straight Vegetable Oil?

If my engine runs on SVO, then can I burn WVO?

How to make your own heat exchanger

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I hope you found  the information on this site useful.  
Do not hesitate to contact us if you have any further questions.

John Nicholson   October 2002   March 2007 June 2007