The Problems with Mixing - Why You Should Convert Instead
We are finding more and more that potential veg oil users are being given misinformation on exactly what they should and should not do to properly achieve their goal, to run their vehicles on vegetable oil. Consequently we've provided information below which we hope will help.
Mixing Vegetable Oil and Diesel
We have been asked so many times “what mix of veg oil would suit my vehicle”, “cant I just throw it in the tank” or “my mate has been running pure veg oil with no problems”, many people state “my mate says”, its funny how many “mates” are experts isn’t it? We have always answered this type of question with a shortened version of the contents below.
First of all let’s get down to the basics of running diesels on veg oil. SVO (straight vegetable oil) is many times thicker than diesel at ambient temperatures, the lower the temperature i.e. in winter, the thicker the SVO, in summer, the thinner it is, but even then it is still many times thicker than Diesel.
The mechanics for successful combustion for SVO is very simple, once it is heated to normal engine temperatures around 80°C + it burns similarly to Diesel. But it really is no use heating veg oil and squirting it into a cold unmodified engine, the net effect is cold start problems as outlined in the following paragraph. Everything, the engine and the SVO going into that engine must be at a similar hot temperature.
There are many common misconceptions about running diesels on veg oil, just because the vehicle appears to start and run okay with a mix on an unmodified engine, then it must be OK? WRONG. It must be stressed at this stage that the following should be read in conjunction with our section on injection pumps.
Vegetable oil ONLY burns cleanly when hot, so when mixing, most of all potential damage will be caused when starting from cold, when the fuel is forced through injectors, the fuel is thicker thereby putting tremendous unnecessary strain on the fuel system pump and injectors, at least shortening their life, the cold veg oil part of the mix does not fully atomize, you need a fine atomized spray of fuel for clean combustion, larger droplets than intended will form, when they are larger they become incombustible, now large droplets of incombustible fuel have to go somewhere, some will be thrown out of the exhaust causing unnecessary pollution and acrid smell, some accumulates on the internals of the engine running the risk of carbon build up which can stick piston rings into their grooves and can damage surfaces on bores. The remainder will find its way down the bores into the engine oil causing greater engine oil contamination than normal.
ALL diesel engines have a certain amount of fuel to engine oil contamination to a greater or lesser extent dependant upon many things, pre-combustion chambered engines tend to suffer less than direct injection engines. This is why, on any diesel, when engine oil is changed it immediately appears black again, this is soot / carbon deposits amongst other contaminates. When diesel contaminates engine oil it thins it out then most evaporates, when veg oil contaminates it thickens due to polymerisation and there is no evaporation. When engines are started from cold on SVO or a mix this ingress can be greatly accelerated. If you find that the dipstick level is rising the sump is filling up, it is a sure sign that your engine oil is being contaminated with veg oil, if left unchecked an overfull sump can cause damage. A simple test for polymerisation is to dip then get sample oil between thumb and forefinger, if it is sticky, CHANGE THE OIL, with converted engines in good condition this does not usually happen until normal service mileage is due, if at all. With converted engines we recommend engine oil changes every 5000 to 6000 miles, a good mineral based oil or semi synthetic oil is okay for some engines but a high spec plant based engine oil such as Plantomot 5w40 is even better as these oils resist polymerization well, conserve energy and are rapidly biodegradable. We advise use of these oils especially on higher powered engines and direct injection types. In extreme cases where the engine has gone way over its service interval and/or engine is not in good repair the engine oil can turn to sludge. BE WARNED.
This all usually happens gradually over time so is not immediately noticeable, it is the false sense of security in which “my mate says” everything is hunky dory. Because there is usually no real noticeable difference except for maybe more smoke out of the exhaust than would be normal but of course “my mate” isn’t bothered is he? He’s at the front driving and the exhaust’s at the back in some other drivers face, of course this is where it really detracts and puts other road users off, and gives us a bad name, because they really do smell strongly of burning cooking oil, or should I say unburned cooking oil, there is a vast difference in the smell of veg oil when it is being burned properly, the faint smell of a barbeque with no more smoke than when running on Diesel is what it should be like.
The above scenario will be lesser or greater in proportion to the amount of veg oil mixed, the ambient temperatures at which it is used and the tolerance to veg oil of the particular engine, generally older pre-combustion type engines will be more forgiving, for instance the older type Mercedes pre-combustion engines are the most tolerant due to their particular unique design than the more modern direct injection engines. With common rail and equivalent PD type engines and those with in-tank lift pumps (some in-tank lift pumps are barely capable of pumping diesel let alone SVO!) and engines with Lucas type distributor injection pumps you can really get into trouble very quickly.
Another problem is that most diesel filters are either inadequately heated or not heated at all causing veg oil to wax up and hinder or stop fuel flow.
Mixing a small amount of veg oil to an unmodified diesel is, however, undoubtedly beneficial. Five percent would probably not hinder combustion and would aid fuel system lubrication. There would also be an improvement in emissions, similar to that of the same biodiesel mix which is widely sold at the pump. We reason that why go to the extraordinary bother of making biodiesel with all the nasty chemical processes that go with a loss system only to mix it with 95% Diesel? May as well just add 5% Pure Cold Pressed Rapeseed Oil but that’s another story!
Taking what common sense tells us into consideration, I am sure that many of you will have come across some great claims on the net, on eBay etc so we will just take a little more time to explain a few further points.
There are many claims by “fly by night manufacturers” of spuriously designed gizmos, “fit this widget and you can start on SVO no problem”. We say you cannot cold start on SVO without some detriment in an unmodified engine period. For instance take the lesson from above, now many so called engineers seem to think that firing up a glow plug in the fuel line will aid starting, this simply is a wildly inadequate modification. Worst still many believe this drivel. How is this even remotely possible? You have several kilograms of cold metal, tubing and fuel and a 150 watt glow plug is instantly going to set the scene for a successful start up? No way, it is just enough to un-wax a filter, granted it may be better than nothing but glow plugs are designed to glow almost white hot for short periods of time, they are not designed for fuel to run over them constantly, this is why you will find that they will fail regularly, also with such high temperatures the risk of carbon build up and break off is very high, whatever you do do not put one of these in front of your injection pump without a high temperature filter to catch any debris (please don't get confused with ATG's diesel-therm which is specially designed for fuel to flow over them, they are built to ATG's specification by glow plug manufacturers, they cannot be bought anywhere in the world other than from ATG or their approved dealers, we are their UK agents, they are used as part of a kit along with a 2500w or more rated coolant heat exchanger). We have made very simple calculations and to be able to do what these makers claim even a small engine will need somewhere in the region of 2,500 watts of power for a clean start if used in the right areas. So 16 glow plugs in a line? Don’t think so, that’s over 200 amps on a 12v system! That’s not forgetting of course the cold veg oil still in the high pressure lines, the cold injection pump, the cold piston tops, the cold bores, the cold everything else!! The only way to make a clean start other than conversion is to pre-heat the whole engine, one way is to use a “night heater” either electrical mains or diesel whereby the engine is heated via heating the vehicles cooling system, with a few tweaks this could be a very successful way to do it but in practice it really is not the preferred method, these systems are expensive and you would need maybe half an hour of heating prior to starting at each and every cold start, the energy used is pretty phenomenal considering it is largely being wasted on a stationary vehicle, for instance if you preheated your vehicle 2 times daily, once to get to work then again for the return trip you would use the equivalent of at least 10 full boiled kettles, or over 7 days lighting for an entire house in energy value EVERY DAY!
Conversion really is THE only feasible, rational answer to running veg oil successfully. Some choose to convert the fuel. We choose to convert the vehicle. With a two tank kit, you start on diesel, run as normal and only introduce veg oil at the correct time/temp, run for as long as necessary, the system is then flushed back to diesel ready for the next morning’s start-up, this completely and neatly eliminates the above problems. In some cases a single tank conversion is possible where injectors and other ancillaries are modified to better atomize veg oil. Many millions of miles have been successfully done using these tried and trusted methods in UK and by a factor of at least 20 in Germany, indeed they already have an approved fuel standard for Cold Pressed Rapeseed Oil.
It’s up to you we can only try to help you make the right decisions, you may well reason that if the vehicle was an old banger of little value then its not worth conversion as it will probably be scrap in another few thousand miles, well yes there is a point but I really would not want to be behind you in a traffic jam first thing in the morning.
We are not selling conversions for fun, it is not a gimmick it is a genuine solution offered to a growing sustainable market. If you’re going to do it and there are many reasons why you should, do it in an informed responsible manner. Do it properly.
If you have any views or comments to make on this article please email: email@example.com
Need Help? More Information?
If you require any guidance or assistance, please contact us - we're happy to help.