What Happens if Diesel Used in Petrol Engine


What happens if you use diesel oil in a petrol car

What happens when diesel is used in petrol engines and vice versa. 

The simple answer is petrol has higher auto ignition temperature and it won’t burn at the compression ratio of a diesel engine without external help. So, the engine won’t run. 

Whereas when you use diesel in petrol engine, it’s dangerous. Diesel burns with more power and it may damage the engine partly or completely.

Now Brief Answer, Let me give you a more logical and factual answer than theoretical one which others have given.

Let me define two terms

(1) Flash point: temperature at which a flammable liquid can convert into vapor. 

Petrol: 42 °C

Diesel: 52 °C

(2) Auto-ignition temperature:
The temperature at which a fuel will auto-ignite and doesn’t need a spark.

Petrol: 280 °C

Diesel: 245 °C

Keeping above points in to mind let’s assume

If petrol accidentally gets into a diesel engine

If you put petrol in a diesel car there are two possible consequences

1) The engine won’t start at all, you’ll have to empty the system, clean through the fuel line, injectors, and spark plugs, and then flush the same way you do with a diesel in a petrol engine. 

Then refill with diesel and take for a longer drive to re-lubricate the system and burn off any remaining petrol residue this is not too much of a problem.

2) Now
if the engine is hot, it can produce temperature high enough to cause
auto-ignition of petrol. 

If the engine starts, the fuel pump which is usually lubricated by means of diesel fuel, is filled with petrol, acts as a solvent, and removes any lubrication the cause of excessive wear and stress. 

The fuel then travels through the delivery system, through the injectors and into the cylinders, but since petrol will ignite far more easily than diesel, compression will most likely cause the fuel mixture to ignite past top dead center. 

This results in sudden jerks as the engine momentarily works against itself. This would put an excessive amount of stress on the crankshaft as it would be forced in opposite directions.

It can also seriously damage cylinder liners and valves. Further damage may include pistons coming into contact with the intake/exhaust valves and raising them completely.

Usually lubricating components seize up because petrol does not contain lubricant like diesel. The cylinder head gasket may protrude along with many other gaskets. 

If the engine continues to run, the engine will overheat very quickly and any seals around the fuel pump etc. will most likely be damaged due to incompatibility with petrol. Overall, the engine will be completely damaged.

If diesel accidentally gets into a petrol engine

will not be able to form vapor in carburetor. This will not allow a
mixture of diesel vapor with air to form. 

So there will be no air-fuel
mixture. There will be only air going in cylinder with no fuel so there
will be no combustion at all.

what if you are running the engine for a long distance? 

Let’s assume
that the car has been running for 100 km . So now the whole engine is
very hot. Now if you put diesel in such a hot engine system, then
temperature of the whole system would be greater than 50 °C. 

This allows
diesel to evaporate, so there will be air-fuel mixture.

will run very poorly, make a lot of smoke and will continue to do so
until you’ve gotten though most of that tank and refilled with proper

performance would not be as desirable because the engine was designed
for petrol and not for Diesel. 

Wrong fueling is like food poisoning for your vehicle. Be careful.

That’s why you can see some people saying
that diesel can work in petrol engine.

However, safety measures are in place at most fuel stations to prevent such an incident. 

It is also unlikely that the engine will continue to run long enough for all of the above damage to occur. 


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