I put petrol into my diesel X5 - PLEASE HELP!!!

[JCL]

Originally Posted by supersteve

Putting Deisel into a Gas/Petrol vehicle is deadly to a gas/petrol engine. Deisel is made to detonate. This is why the engines are so heavily built. The nock of a deisel engine is the fuel detonating. That much detonation in a gas/petrol engine will make part go there separate ways rather quickly.

Well, if we want to be precise, diesel fuel is meant to ignite, the same as petrol, and not detonate. Detonation is, strictly speaking, an explosion that creates a shock wave.

Diesel engines are more heavily built because they have higher compression ratios, not because of the fuel. We should differentiate between the diesel cycle (compression ignition) and diesel fuel (or plain old #2).

Diesel fuel has a lower octane rating (AKI) IIRC, so it is harder to light up. Since it has less resistance to pre-ignition, it won't work very well in a petrol engine, as you rightly point out. I like your phrase about the parts going their separate ways. Best phrase I ever heard for that was in Australia; the colloquial expression was 'kicking a leg out of bed' in reference to a connection rod protruding through a crankcase.

[supersteve]

JCL,

We are saying roughly the same thing. I do disagree with the reason for deisels being built heavliy though. The compression pressures are required to ignite the fuel. What came first, the chicken or the egg.

There is no spark plugs in deisel engines. To start the engine glow plugs are used; but, after starting they are no longer powered by the battery. Some engines use flame chambers and some use the glow plug which continues to glow from the previous burn in the combustion chamber. Most of todays engines use the heat in the engine combined with high compression to "ignite" the fuel. As a result, the fuel does detonate. This is the reason deisel engines have there characterisict knock. Also why, when a very poorly tuned gas/petrol engine (almost unheard of today) runs after shutting off the key. It's called deiseling. The fuel is burning without the spark plug lighting it.

Deisel fuel has much more energy in it than gas/petrol. This is the reason for being able to turn the engine so much slower and still be able to produce so much torque. The resultant lower RPM and high torque is where the much greater mileage comes from.

Turbine engines use kerosene, IE deisel fuel, jet fuel, JP1,2,3. Because of the energy level in the fuel. Gas/petrol, IE avgas, can be run in aircraft turbine engines but the inspections are more often and the power output is reduced. It takes more gas to produce the same power resulting in higher temps in the engine. I could go on. . .blah, blah, blah.

End result. . .gas/petrol in your deisel engine will be ok short term. Deisel in your gas/petrol engine will be deadly to you engine.

[JCL]

Supersteve

I think we are fairly close. A couple of clarifications:

The compression pressure doesn't ignite the fuel in a diesel cycle, the compressed intake air does. It is a matter of timing. The air is hot because of the compression process, but the fuel is injected after the air is hot, so the compression stroke doesn't actually ignite the fuel.

Diesel fuel doesn't normally detonate in a diesel cycle engine, it burns. That burn is a controlled process, with a predictable flame front. In a diesel cycle, that process includes lean, stoichiometric, and rich burn phases. Detonation is an explosion, with an unpredictable flame front. The detonation noise (rattle) is caused by the shock wave from the flame front. In a diesel engine, the knocking noise is generally caused by the high compression. While there may be detonation, it is an exception and not the intention.

Dieseling after turning the engine off refers to self-ignition, as opposed to spark ignition. Agreed. That is in reference to the diesel cycle, though, as contrasted with diesel fuel. Two completely different things. Diesel fuel is a fuel we commonly use in Diesel cycle engines, but it can also be used in other engine designs, notably turbines.

#2 fuel oil is commonly referred to as diesel, and is also used for home heating oil. It is not the same as the various categories of jet fuel, which are generally closer to Kerosene (#1 fuel oil). Let's leave turbine fuels out of it, we have enough here with the Otto cycle and Diesel cycle.

We do agree that diesel fuel in an Otto cycle engine is a bad thing

[supersteve]

Originally Posted by JCL

We do agree that diesel fuel in an Otto cycle engine is a bad thing

Absolutely

[x5z]

once i burn al the fuel by drivng, do i just fill it up with diesel again or is there a cleaner i need to put in the tank?

also will i need to change the fuel filter or anything else?

[PompeyGirl]

I accidently once filled up with petrol into a Jeep Grand Cherokee (2.5ltr TDi) i had. I only had a few gallons of Diesel in at the time and run it until it started to make horrible noises and eventually stopped.

The AA chap said the following to me:

1) Its far worse putting diesel into a petrol engine
2) You must drain the tank fully in either senario
3) You must change the fuel filter
4) Petrol in a diesel engine will eventually wear out many rubber seals and gaskets, hence why BMW claim a min of £2k from insurance companies because they change and swap out most of the fuel system components apparently.

I paid for the tank to be drained, fuel filter change and rubber gaskets here and there and sold the car a month later.....

[Windermere]

I did the same - about 30 litres on top of a quarter tank of remaining diesel. I switched on and moved the vehicle about 100 yards before I realized what I had done.

Then a tow to a friendly neighbourhood garage, and the tank drained (through the pipe under the hood) and re-filled.

The engine seems fine (so far) and we continued on our way.

The important thing to note is that the tank won't drain unless you turn the ignition key sufficiently to activate the pump - but this seemed to do no harm.

So.... a relatively inexpensive re-start and I consider myself dead lucky

[TrickerZ]

Originally Posted by supersteve

JCL,

I do disagree with the reason for deisels being built heavliy though. The compression pressures are required to ignite the fuel. What came first, the chicken or the egg.

Compression is required, and a strong block is required to hold that pressure without warping cylinders. It's the same reason boosted petro and high compression direct injection motors have thicker sleeves and beefier blocks.

The compression causes the fuel to mix with the air more evenly and also produces more heat for ignition.

Back on topic, as long as the car still ran ok, there was not enough petro in the motor to do any damage. Seals will dry out over extended exposure to petro, so a full tank of petro would be a concern, but the ratio you had was low enough it shouldn't cause any issues. I would change out the fuel filter after filling up with diesel a couple times and that's it. All the other stuff they would do is a "just in case."

[318i318is328i645i745ix5]

I did this recently and hope my experience will be useful....

I filled up an almost empty tank of diesel with unleaded petrol. Luckily we drove only about 50 meters and parked up idling while we devoured some pizza. The car was idling for about 5 minutes and then started shake.

I was still unaware and i started to drive and realized its shaking quite a lot....i switched of the engine and started again....It continued shaking...it then dawned on me that i had put the wrong fuel so i turned it off.

We had the car towed to the nearest bmw...they drained the fuel tank and changed the fuel filter....and luckily the car is absolutely fine.

[X5Sport]

I think you can count yourself extremely lucky. Petrol in a Diesel BMW frequently results in not only a new engine, but a new fuel injection system too. A friend of ours did this recently do a E46 330D and it cost him well over £10k plus fitting. He got about 1/2 mile before it all stopped.

If you do inadvertantly repeat the misfuelling and put 100% petrol in, the official advice is do not turn the key. Even with the engine stopped, the fuel pump activates at Pos 2 and will pump the petrol though the system and cause irreperable damage to the seals in the injection system and that will be that.

I'm thinking of putting one the the more widely available anti-misfuelling devices into the filler of the tank. They only open with the wider diesel nozzle in place as the narrow petrol nozzle will not open the valve so you can't misfuel. Now we only have diesel BMWs in the stable it's less of a worry, but still an easy thing to do. I always double check what the nozzle says before squeezing the trigger - especially at night when I'm tired.