I have a A200CDI '05 and a R320CDI '07 and was wondering if I could literally pour in Veg oil in the tank with a 50:50 mix and drive away...
Or is there a catch?
Hi Rob, I'm not an expert, nor a mechanic, but I did a fair amount of research before pouring cooking oil into the fuel tank of a £25K S-class.. and I would say you would have no problems at all.
Here are the key points from my research (please note it is knowledge gathered by research - and not the knowledge of an expert !).
The 'Diesel' engine was not originally designed to run on what we call 'diesel' nowadays - it ran on oil.
Veg oil will not harm your engine at all, unless you run on 100% when you
may get some 'coking' in the engine (deposits due to incomplete combustion?) which can be blown away with a good hard 0-70 blast at full throttle now and again. A few sites I visited said you actually get better upper-cylinder lubrication with veg oil so it is actually better for your engine than diesel.
It can however harm the fuel pump due to being slightly thicker which makes it harder to pump, this is a problem in cars with a Lucas or CAV fuel pump, but as long as you have a Bosch fuel pump you are OK due to their different design and tank-like build quality (MBs have Bosch pumps).
When the oil is cold it is thicker than diesel so doesnt quite give the same spray pattern ('atomisation') from the injector, so doesnt combust quite as well (hence the coking mentioned above) which means on a cold start the engine might take longer to start .. in my experience only noticeable when I was running 100% or in the freezing winter, when the car turned over for maybe 5 seconds longer.
Because the fuel pump is phsically bolted to the side of the engine block, is soon becomes very hot when the engine is running, and because the flow of fuel is relatively slow, the oil gets warmed up while it passes through the hot pump and lines so becomes much thinner due to the high temperature. The viscosity problem is therefore only an issue on a cold engine (and only at higher concentrations).
In extremely cold weather veg oil can go thick and form a 'sludge' (my dad used to call it 'waxing' when he ran tractors with red diesel 30 years ago when diesel didn't contain additives). This is bad news as the oil effectively becomes a semi solid and you need to heat it up to get it flowing. I believe this is only a problem in the VERY cold weather and can be prevented by not going beyond 50%. It never happened to me.
Real enthusiasts install a second fuel tank with 100% veg oil, they start the car using diesel, then switch over to oil when the engine is warm, then back to diesel for 2 minutes before stopping to fill the pump and lines with diesel again ready for the next cold start. You can even run your hot radiator pipes through the tank to warm the oil (not much point though as it gets warmed when it gets to the hot fuel pump anyway).
I did get caught out once when my wife had a Fiat Bravo hire car which I filled 50% with oil. It just didn't like it and wouldn't start. I put a fan heater under the bonnet to warm up the injector pipes on top of the engine for 5 minutes ant away it went ! Just needed the oil thinning down with a little warmth. I think the Fiat diesel engines have a different invector system.
That's pretty much what I know - I hope it is helpful.
I believe you would have no problems at all using 50%. The engine certainly runs quieter (less knock) and the exhaust produces a lovely sweet 'doughnut' smell.
Best not to fill the tank right up - so that it can 'slosh around' and mix the oil and diesel together. Also put the diesel in first. Fill the tank one-third full with diesel, then take it up to two-thirds with veg oil, that leaves a good head space to allow mixing on the speed bumps ! Literally just pour it in the filler.
The 3-litre bottles are a good size, and when you've had practice you can get it in without spilling a drop. You then drain the dregs from the empty bottles by standing them upside down on top of another bottle to empty out fully (waste not want not !). Buy the cheapest 'own brand' oil - it is thinner which is good. You should use Rape Seed Oil - if you look on the label of ordinary vegetable oil it will almost certainly be rape seed oil. Sunflower oil is more expensive and thicker, but would work.
I have heard that the oil will 'clean out your tank' - possibly as it is thicker so any dirt will be suspended in the oil and carried through the system. Don't worry - that's why you have a fuel filter. A few people say you will need to change your filter after using it for a while - but I have been using it for 18 months and still haven't changed the filter.
I think at 50% you are being quite conservative and would have no problems, maybe down to 25% in freezing weather to be totally safe.
At nearly £1 per litre the savings aren't as big now - but still cheaper and it's nice to know you're saving the environment too (they claim the CO2 you produce when burning the oil is only the equivalent to the CO2 the plant removed when it was growng - so cancels it out - a zero carbon footprint !).
It has always been legal, but until July 2007 you needed to let HMRC know you were doing it and send in a return every month with a cheque for about 20p for every litre you had used. They have scrapped that system in July 2007 and you are now free to use veg oil (or any other bio fuel) without the need to notify them, as long as you don't use more than 2500 litres per year.
Please note these are only my personal findings and I can make no guarantees ! I currently run an S320 (3.2 litre 6 cylinder diesel) and a C220 Sport Coupe (2.2 litre 4 cylinder diesel) and they are both more than happy on a staple diet of 50% veg oil.
All the best.
