Petrol in a diesel engine

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ed2288 | 00:13 Fri 07th Jul 2006 | Motoring
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Hi. Will putting 0.75 litres of unleaded petrol in a diesel car before realising the error and then filling up with 35 litres of diesel cause a problem?


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Oh the shame ........ I put a couple of pounds worth in a totally empty tank that cost about forty five to fill. There is a cut of ratio of around five( ish ) per cent. I was told to NOT start the engine but to carry on filling with diesel , as much as it was humanly possible to squeeze in , and to top up as frequently as possible. I have to say bmw still fine, but above this ratio the advice would have been to stay put. Do NOT start engine and await recovery - cheaper than new engine!
I found this:

Don;t worry, it will be fine. You may use upto 15% petrol in the diesel in
the winter months to prevent waxing (of summer grade diesel) and improve the
cold start performance anyhow.

Aparrently it is a favourite trick of black cab drivers to keep their vehicles running.

No need to worry at all. Thats a very small ratio and not worth even thinking about. I have often put a gallon of petrol in my diesel to clean out the fuel pipes and give it a little "perk up".
They did an experiment on this once on fifth gear and completley filled a diesel with petrol and it ran fine, but then wouldnt restart until they put more diesel in!
try it the other way round and you'll find you've got big problems.
It�s worth looking at the differences between petrol and diesel to understand the effect the wrong fuel will have on an engine. Firstly, diesels are correctly known as Compression Ignition Engines. That means they use the heat generated by compressing the air in the cylinders to ignite the fuel when it is injected. Diesels compress only air in their cylinders as opposed to petrol engines that compress a mixture of both air and fuel and use a sparkplug to ignite the mixture.

The fuels themselves are also quite different. The most common measure of fuel quality for petrol is its octane number, a measure of its ability to resist �knocking� or self-combustion. On the other hand, diesel�s quality is specified by its cetane number, which is a measure of its ignition properties. Simply, one is a measure of how resistant the fuel is to self-ignition and the other is a measure of how well it ignites.

In addition the timing of injection in a diesel engine takes into account the combustion characteristics of the fuel. For instance the time it takes from the point of injection to when the fuel actually begins to burn is important in selecting optimum injection timing. Too early and the piston will still be on its way up and too late will mean that some combustion energy will be wasted. As you can imagine introducing a fuel with the wrong combustion characteristics will have a major impact on performance, and could potentially damage the engine.

Diesel fuel injection equipment relies on the fuel for lubrication. Diesel fuel has lubricating properties but petrol is a solvent that can strip lubricant from moving parts allowing metal-to-metal contact and damage to the very precisely machined (and very expensive) components.


But while an older style diesel engine may tolerate a small amount of petrol (although it definitely isn�t recommended) without too much damage, the newer Common Rail Diesels are unlikely to tolerate any level of petrol without damage. Australia has only recently begun to receive these new engines, but in Europe, where diesel engines are common in passenger cars and where Common Rail diesel engines have been in use for some time, the problems associated with mis-fuelling are well known. In fact it has been reported that vehicle manufacturers are providing their European dealers with detailed instructions about the corrective actions needed in the event of a mis-fuel.

Obviously the extent of the work required to rectify a mis-fuel will depend on the type of vehicle and how long it has operated on the wrong fuel. But in the worst case expect a bill for several thousand dollars as rectification could require repair or replacement of much of the fuel system as well as repairs to the engine itself if it has suffered damage. The best case, where the fuel has been put in the tank but the engine wasn�t started, will involve draining the tank, adding the correct fuel and bleeding the system of air.

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Petrol in a diesel engine

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