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5110 Days of genuine trouble-free motoring on veg oil from 18th June 2008 to 16th June 2022 - read more

Painful Lesson Learned

WARNING - There are drawbacks to running a vehicle on vegetable oil

Probably the biggest problem and drawback associated with converting your car to run on vegetable oil is the cold start problem, something I discovered only too well within a couple of months of converting. Put simply, because I forgot to flip a little switch one afternoon, the following morning I couldn't start my car. I'll explain more about this below, but first a few pertinent questions:

  • Why is it important to use a two-stage system?
  • Why is it important to start using diesel?
  • Why is it important to remember to switch back to diesel near the end of the journey?
  • What happens when you don't switch back to diesel?
  • How do you start a cold engine full of vegetable oil?

There's a lot of question above and they're there for a reason. All of them are answered in what follows and may be of use to someone else browsing this site for information.

So, let's look at the problem...

Forgetting to switch back to ordinary Diesel

As I said above, simply because I forgot to switch from Vegetable Oil to Ordinary Diesel two minutes before the end of my day's journey, the following day I couldn't start my car because the engine was full of vegetable oil.

Vegetable Oil and Cold Starting

Because vegetable oil is viscous, it has trouble squeezing through all those necessary parts that make your diesel engine run, and most particularly through the injectors. Hot vegetable oil has little trouble because it's nice and liquefied, but the colder the vegetable oil, the thicker and more viscous it becomes, and the harder it gets to start an engine.

Not all cars are the same. Older vehicles with more basic diesel engines tend to be fine with pure vegetable oil, even on cold days, though they may have to crank a while to start. However, modern diesel engines, such as that found in my car, just can't cope.

When I came to start my car it was a cool summers morning, around 7.30am with a temperature of just 14°C. I sat down, turned the key and listened to the sound of an engine that just wasn't going to start. I must have sat there five minutes trying and trying again, but there was no way that cold vegetable oil was going to start my engine - and the engine and fuel pipes were full of it.

Understanding the Two-Stage System

If I haven't made this clear elsewhere, this is how a two-stage vegetable oil conversion system works.

  • Start Up - at the start of the day, the engine uses diesel to start.
  • Turn On - the system is turned on (from 0 to 1) but nothing seems to happen yet
  • Warming Up - as the car travel, the engine warms up but still runs on ordinary diesel.
  • Veg Oil - once the system detects that the engine has reached a critical temperature, the fuel is switched automatically from ordinary diesel to vegetable oil.
  • Green Running - the vehicle now happily travels on this natural, biodegradable, fuel.
  • Journey End - two minutes before reaching your final destination, i.e. one where the vehicle will sit long enough to get cold, the system must be switched off. This Purges the fuel lines and engine so that it can start more easily on ordinary diesel.
  • Turn Off - with diesel in the engine, the engine can be turned off.

As you can see from the above, ordinary diesel is still very much a part of the two-stage process, but it's use is significantly reduced. From my personal experience, I've found I use somewhere like 75 to 85% less ordinary diesel, which is kinder to my pocket and the planet.

The Importance of the Two-Stage System

It should be clear from this why a two-stage system is critical to the modern diesel engine. Without that initial run on ordinary diesel, most modern engines simply wouldn't start. Furthermore they are prone to wear and damage.

My Mistake - The Consequences

By failing to switch off the system, I failed to provide my engine with enough diesel in the engine and fuel pipes to get it started. If it had been a hot summers day, maybe I would have stood a chance, but that was not to be. Consequently I needed to find out how to start on engine full of cold vegetable oil.

DieselVeg To The Rescue

Credit where it's due, I telephoned the guys at DieselVeg (DieselVeg no longer trade - click here for other fitters) who fitted my system and told them the story. It's one they've heard many times before. I guess everyone running this system makes this mistake sooner or later.

Thankfully the solution didn't involve anything too mechanical otherwise my meager talents may have caused me problems.

How To Start A Cold Engine Full Of Vegetable Oil

The answer to the problem lay in a two strange places, the kitchen and my wife's dressing table.

After guiding words from DieselVeg, I removed the large protective cover from my engine, located the common rail (or to the technically minded like myself - the metal bit with lots of metal pipes coming from it on the side of the engine block). From there I set about heating this up with a combination of hot water (being careful to avoid electrics) and my wife's hairdryer.

Sure enough, after several minutes the metal became hot and, presumably, the oil within it became more viscous.

After some more noisy cranking of the engine, it finally caught and started. I didn't hang around and took it out for a quick run to get things moving again.

Lesson Learned

So will I make the same mistake again? I'm bound to. But at least I know the solution now.

However, the solution is timely and awkward, so clearly it's better not to have to use this if it can be avoided. So please, learn from my mistakes - not yours.

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