Mercedes SUV's Diesel Engine Runs Out Of Control, Truck Drivers Come To Help [Video]

Imagine you are on a road trip with your expensive German car and at some point in time, it starts behaving weirdly. You see the RPMs rise beyond control and white smoke coming out of the exhaust. Thankfully the car is parked and doors are open. You are left clueless as to what the issue is...

Well, this happened to someone recently, the video of which has now surfaced online. Interestingly, passing truck drivers showed up with help. This unfortunate incident happened in Coorg, Karnataka. In the video, we see a Red Mercedes Benz GLA parked to the left side of what looks like a Ghat road.

The doors and tailgate are all open. The engine is running beyond recommended rpms. Thick White fumes can be seen coming from the exhausts. The driver clearly has no control over the engine or its rpm.

The driver is seen taking something from the cabin - probably valuables, as he could be foreseeing a fire. Later in the video, we see a truck being parked nearby and its driver and crew getting out. The driver has a fire extinguisher in his hand.

They rush to help the Mercedes Benz driver out. In this clip, we see the GLA's hood open. The truck driver is seen using the extinguisher into the engine. Soon, the engine is brought to a halt and hopefully saved from complete self-destruction.

What Happened Here?

This seems to be a case of what is known as 'Diesel engine runaway'. It is indeed a diesel owner's nightmare, as the engine essentially enters the self-destruct mode and no insurance is going to cover it! It used to be a common issue in the bygone era.

It is, however, a rare occurrence in modern diesel engines and this Mercedes owner just happened to be extremely unlucky! In most diesel engines of our time, Electronic Control Modules (ECMs) can monitor fuel accurately and possibly prevent this from happening.

Before going deeper into the issue, let's take a look at how a diesel engine functions. A petrol engine uses spark plugs to ignite the air-fuel mixture. When it comes to diesels, pressure plays a key role as well. These use compression-ignition and glow plugs that are constantly heated.

The air-fuel mixture falls into the combustion chamber and not into ports as they would in a petrol engine. Petrol engines usually use a 8-12:1 compression ratio. For most of the modern diesels, it is at least 14:1 (could go up to 23:1)! Modern diesel engines use direct injection and throttle the fuel going into the cylinders- it isn't upon butterflies to regulate the process.

Diesel Engine Runaway: What Is It And Why?

In simple terms, it is a diesel engine that spins at the maximum possible rpm and one which would not stop even if you turn the ignition off! It draws excessive fuel from an unintended source and continues to spin until a catastrophic mechanical failure is achieved.

Poor maintenance, age and neglect could lead to this condition. Pumps that tend to meter too much fuel, oil seal failure, overfilling the crankcase, broken or damaged internal fuel pipes, incorrectly assembled or faulty linkages can all be possible causes of a runaway. It could also happen if the vehicle happens to be in an environment contaminated with hazardous vapours or hydrocarbons.

How To Stop A Runaway Diesel?

As mentioned earlier, switching off the ignition is not an option! Remember, the engine is in a self-powered mode, when in runaway. It has ample (read 'excess') fuel to feed on, unrestricted airflow, and unhindered compression ignition.

The only way to stop it is by removing any of these facilitators. The only possible thing to remove would be the airflow. Smother the engine by closing the air intakes, till it comes to a stop. A CO2 extinguisher can be used for this purpose, like the truck driver did in this case. Yes, getting to the intake of a vehicle undergoing runaway could be tricky...