One of the most terrifying situations a diesel car owner can encounter on the highway is a sudden turbocharger failure. Initially, a distinctive, police-siren-like whistle is heard in the cabin, followed by a thick tail of bluish-grey smoke trailing behind. If correct decisions aren’t made at this critical moment, the situation can escalate into a catastrophe – the so-called diesel engine runaway process (Engine Runaway).
What Is Engine Runaway and Why Does It Happen?
A diesel engine operates on the principle of fuel mixture self-ignition under high pressure. Unlike petrol engines, diesels don’t use spark plugs. When the turbocharger rotor shaft bearings wear out and the seals fail, the turbo’s lubricating oil, under high pressure, begins to pour directly into the intake tract and intercooler.
Once it reaches the cylinders, engine oil becomes an uncontrollable fuel source. The engine uncontrollably revs to maximum RPM, often reaching 5000–6000 RPM and far exceeding the redline. At this point, removing the ignition key won’t stop the engine, as it’s no longer drawing fuel from the tank but burning its own engine oil!
How to Mechanically Stop a ‘Runaway’ Diesel Engine?
- For cars with a manual gearbox: Depress the clutch pedal, engage the highest gear (5th or 6th), press the brake pedal all the way down with both feet, and quickly release the clutch. The immense mechanical resistance will instantly stall the engine.
- For cars with an automatic gearbox: It’s not possible to stop an automatic transmission this way (switching to P or N will only increase RPMs). The only option is to open the bonnet and block the air supply to the intake (using a thick jacket, a floor mat, or by discharging a powder fire extinguisher into the air filter). Caution: Never place your hand near an open turbo intake!
Actions After the Incident
Under no circumstances should you attempt to restart the car. The intercooler and cylinders will be full of liquid oil, and any attempt to restart will cause a hydrostatic lock. The only correct course of action is to call for assistance. Our 24/7 recovery services will ensure your vehicle is gently loaded onto a platform with a winch, and our transparent recovery service pricing will protect you from unpleasant financial surprises.