Simple one - I've heard different stories about running a petrol engine on diesel being safe (but smokey) while running a diesel engine on petrol (or a mix of petrol & diesel) is rather catastrophic. Some people tell me this is true, while some insist that the reverse (running a petrol engine on diesel) is the dangerous one.

Can anyone enlighten me, and would this opportunity to blow vehicles up conduct a suitable experiment in the name of science interest someone?

Running either engine on the other fuel 100% is impossible.

A petrol engine does not have the compression ratio necessary to ignite diesel.

A diesel engine would ignite the petrol mixture way before the piston had reached TDC and push it back the wrong way.

However, a small percentage of each fuel will work in the other.
A petrol engine will burn a petrol/diesel mixture up to about 5% but will smoke and possibly damage the catalytic converter as the management system would not be calibrated for the diesel.

A modern diesel engine however will run reasonably well on up to 40% petrol. I know this to be true because i accidentally put petrol into our company van along with the diesel already in the tank and the only difficulty was it didn't like starting, but once going it didn't appear to bother it in the slightest.

Lorry drivers used to add a couple of gallons of petrol to their diesel in winter to stop in waxing. Modern diesel shouldn't because of the additives.

quote:

A modern diesel engine however will run reasonably well on up to 40% petrol. I know this to be true because i accidentally put petrol into our company van along with the diesel already in the tank and the only difficulty was it didn't like starting, but once going it didn't appear to bother it in the slightest.

My experience is slightly different. I once put about 5 litres of petrol in my diesel car by mistake, and then filled the rest of the tank with 45 litres of diesel. The engine seemed to run fine, but there were a few problems.

The unburned diesel that came from the exhaust condensed onto the rear of the car, making it rather dirty and waxy. This in turn degraded the rubber in my rear windscreen wiper. Worse however is that the rubber in the fuel lines also degraded, and eventually it started leaking. The engine didn't start very well, because some it its fuel was leaking out over the engine. This would then start to smoke, and the smell would come into the cabin.

All in all it is not something I would recommend.

Our company van is probably not the most technologically advanced engine on the planet (it's a Mercedes Sprinter 4 years old), but it didn't seem to bother it unduly when i half filled it with petrol. The only problem was getting it started as the compression was obviously making the engine kick back, but as soon as i sprayed some 'easy-start' (methanol based additive) into the air inlet it fired up and ran o.k.
It may be my imagination but i would have said it ran better - certainly felt a bit more energetic than usual.

I can't understand how the fuel lines would not like petrol but cope with diesel. Diesel is used as a penetrant in many applications because of it's very 'searching' nature, so if any leaks were going to be evident the diesel should find them anyway, and both fuels are produced from the same base material.

Just had a £500 bill to clean up my diesel engine after putting petrol in it. It ran for over 30 miles before I got it to a garage. One of the thing they said was that because the petrol is less dense, then the petrol goes to the top of the fuel tank and so the mixture was Diesel rich which allowed the engine to continue to work.

Sparko says: With it being so easy to put in the wrong fuel, what can be done to prevent it happening... make it impossible to put in the wrong fuel... the potential damage to done by making a split second wrong decision at the pumps should be made impossible rather than undesirable. Prevention must be the only solution. Ideas please on how to achieve this at the pumps.

quote:

Sparko says: With it being so easy to put in the wrong fuel, what can be done to prevent it happening... Ideas please on how to achieve this at the pumps.

In Europe it is already the case that diesel pumps have a bigger nozzle than petrol pumps. The diesel nozzle does not fit into the smaller tank opening of petrol cars. This at least prevents the worst mixup from occurring (diesel in petrol engine) but does not hinder the reverse (petrol in diesel engine).

quote:

In Europe it is already the case that diesel pumps have a bigger nozzle than petrol pumps. The diesel nozzle does not fit into the smaller tank opening of petrol cars.

Not true in the UK, I killed a Ford Orion by putting diesel in it.

The only sure way of preventing it would be to have totally separate pumps for petrol & diesel.

A few points to clear up:

Just because lorry drivers put petrol in diesel all those years ago doesn't mean its ok now, different fuel systems etc.

Try getting a pair of latex gloves drop one in diesel and one in petrol, you'll see what happens. Due to manufacturing cost etc fuel pipes and components for petrol and diesel may well be made of different materials. So the wrong fuel may well damage the pipes and seals.

Diesel fuel systems rely on the "oilyness" of diesel to lubricate them. Petrol often has been used for its degreasing properties. So the more petrol the less oily the fuel.

Although modern fuel systems are somewhat forgiving, there's always some damage done however slight. I suppose the thing is risk factor. Put wrong fuel in your £100 runabout, what can go wrong, the garage bill would probably be more than the car is worth. Half fill your 4 month old car that cost £19,000+ on finance with the wrong fuel, turn the key and you've got a big bill (not covered under warranty).

Best advise overall: Don't do it. If you do by mistake seak advise.



About the fuel pump nozels, hey remember the toy as child where you had the box with the different shaped holes and you had you match the shapes to the hole. Well YOU CANT GET A SQUARE IN A TRIANGLE HOLE CAN YOU (sorry for shouting). Can't the fuel pump manufacturers develop different shaped nozzles. Seams easy to me .

it has long bee known that a common rail diesel engine will run on Nut oil and I believe that it what the first diesels were designed to do.
a good quality veggie oil is a great substitute for diesel oil and I do not understand why the mythbusters didnt explore this one further.
in the summer months when temperatures are above 10 degrees C It is possiable to run my diesel citroen on veggie oil ( pure rapeseed oil)with a return of around 80 miles per gallon long distance at 70mph the milage gained is so significant that I believe the UK goverment will not endorse the use of pure veggie oil for burnning in diesels because it lasts so long.
my vechicle a citroen 1.9 turbo diesel with a stanadyne fuel heater inline with the heated fuel filter runs great but as I said only in the summer can you use this oil neat, in the winter it is Not advisable to use more than a 50/50 mix of diesel and veggie oil, the taxation system for the honest person is a little screwey to say the least at present you only declare what you use so you only pay tax currently around 30 pence per litre on what you burn it is not as yet based on milage.
If you want to declare only half your useage you can do. there are certain engine requirements some fuel pumps won't accept veggie oil and the shafts break leaving you with an extreemly expensive bill to payfor repairs, if you want to try it out don't do it with a new car because the manufacturers will void your warrenty if they find any oil in your fuel. use an older car a peugeot diesel or renault diesel but make sure you have the correct fuel pump before you commit to experimenting, I could tell you whichnpumps are best but if i do there will be no veggie oil on the shop shelves tommorrow and I will be grounded, use the net/web and have a look around you will find the answers.
A word about people putting petrol/gas into diesel cars and vice versa the uk pumps used to warn people with a recorded message when they picked up a diesel nozzel now they don't for some strange reason simple technology and effective I would have thought.

one final word on burnning veggie oil in your common rail diesel engine.
never put veggie oil in an HDi High pressure diesel injection engine the fuel injection nozzels are not designed to take anything thicker than diesel fuel.
There are one or two companies doing conversions at the moment costing around £1500.00 to convert your diesel to run on neat veggie oil all year round if you have lots of money you might consider this as an option but there are cheaper ways around it and there are some reasonably priced kits comming out of Austrailia at the moment for about £500.00 where you have a small diesel tank in you boot and your main tank holds the veggie oil there is a two way valve in the kit with a switch that you mount in your dashboard when you start your car on diesel you warm up the engine and switch over to veggie oil but you also need to swith back to diesel before you stop you engine to clear the fuel lines of veggie oil.
it is much easier to add a little oil to the main tank and mix it with diesel fuel in the winter running higher strengths in the summer.

A WORD ON CATALYTIC CONVERTERS
my s reg diesel had a catalytic converter fitted when I bought it, I researched the possability of replacing the catalytic converter with a standard exaust pipe and low and behold I found out that diesels do not need catalytic converters mine has passed four MOTs without the catalytic converter and my exaust costs have dropped from £350.00 to £90.00
petrol engines on the other hand must have a catalytic converter to pass UK emmissions tests.
if you own a diesel it is worth exploring the previous models to see if any of them have exaust systems without a cat that will fit your car, it is a requirement of the manufacturer to fit catalytic converters to all cars including diesels not the customers responsibility, I believe there are many people who remove their petrol engine catalytic converters and box them up only to put them back on the vechicle at MOT time ensuring that the cat lasts a very long time without having to replace it at unecessary expense.

quote:

petrol engines on the other hand must have a catalytic converter to pass UK emmissions tests.

There is no requirement within the current MOT test for a car to be fitted with a catalyst. Some petrol cars will pass the emissions without one and some won't. Just to clear that up.