What to do in a runaway diesel situation?
If a diesel engine runaway occurs when one is driving, the accelerator pedal should be lifted, and the brakes applied. Do not pull the key out of the ignition while moving (see more below). The car should then be pulled over as soon as possible. You will want to carefully use the brakes and control the steering to the best of your capabilities. Try to gain as much control of the car as possible, and once the vehicle is in a safe and secure place, you want to shut off the engine.
The following are just simple suggestions for dealing with a diesel engine runaway. This will not be effective for every diesel engine as all machines are different, and what can work for one may not work for another.
- Release the accelerator: If the runaway is not strong, taking your foot off the accelerator can cut off the fuel supply to the engine and halt the runaway situation. Since the engine needs fuel to run, this should slow the engine, but if the runaway is already continuously feeding off an unintended source, e.g., its own engine oil, this will not cause the engine to stop on its own.
- Shift to neutral: In cases where taking your foot off the accelerator does not slow the engine, shift the vehicle into neutral. This will hopefully stop any further acceleration.
- Block the air intake: Physical blockage of the air intake can be done with a piece of cloth, a cover, or a plug. This starves the engine of the air needed to sustain combustion, and hence the runaway stops. Or use a fire extinguisher to smother the engine. If a C02 fire extinguisher is available, then it should be sprayed towards the air inlet. This feeds C02 into the combustion cylinder leading to a stop of the combustion.
- Operating the decompressor: If the engine is the engine is fitted with a decompressor, you can stop the runaway diesel engine by operating the decompressor.
- Engage in a higher gear: From diesel engines that operate on a manual transmission, you can often stop the engine when you shift to a higher gear. Keep the foot brake and parking brake fully applied and let out the clutch fast, which should slow the engine RPM to a stop. This causes the engine to stall out, but you must make sure you are pressing the brake.
- Important: When still rolling, refrain from pulling the key out due to the steering wheel lock mechanism. Many people have the impulse to remove the key out of the ignition in the event of a runaway diesel engine because they believe this will cut all power off to the engine and cause it to stop instantly. Runaway diesel engines don't work that way. Even if the key is out of the ignition, the vehicle can still accelerate since it runs off its engine oil. Most diesel cars are equipped with a steering wheel lock mechanism when the key is taken out of the ignition, so doing this in the case of a runaway engine scenario takes away your control of the vehicle. The steering wheel will look, but the engine will still run, and you will have no way of turning or steering the car.
In an instance of a runaway diesel engine, it is most important to remain calm and regain control of the vehicle. In the occurrence of a runaway engine, the engine is already destroyed, and you should never risk your life or another's to help salvage the engine.