You probably don't like the thought of your truck running away from you, but it's a situation you may need to worry about if you drive an older rig. Although a runaway diesel won't take off down the road without you, it will behave in some unusual ways. Unfortunately, this behavior can also lead to lasting and expensive engine damage or even critical failures, such as fires.

On the bright side, runaway is a relatively rare condition, and it's one that you can often avoid by recognizing and repairing problems before they become too severe. Understanding why it happens and how to prevent it will help you extend your truck's life while also avoiding potentially dangerous situations.

Runaway Defined

You might recall the ideal gas law from high school chemistry. Don't worry if you don't, because the concept is relatively simple. This law states that a gas's pressure, volume, and temperature (such as the air-fuel mixture in your truck's engine) are all related. Increase the pressure, and the temperature of the mix will also increase.

Instead of using spark plugs for ignition, diesel engines rely on this relationship to create heat for combustion. As the gas and air mixture compresses, their temperature increases, ultimately igniting the whole thing. In other words, the only things your engine truly needs to keep running are a supply of fuel and air.

This design is what makes runaway possible. If extra fuel enters the combustion chamber, the engine can keep running even if you turn your truck off. The pumping action will continually draw in more air, allowing combustion to continue until the air supply becomes blocked or the diesel runs out. This situation will ultimately cause the engine to overheat, fail, or even catch fire.

How Runaway Affects Older Diesels

Modern diesel engines use computer controls to monitor fuel input, allowing them to detect and avoid most runaway conditions. However, older trucks won't necessarily have this equipment. The best options for preventing runaway in these vehicles are regular maintenance, routine inspections and repairs, and retrofitted aftermarket overspeed protection devices.

In particular, you should never ignore issues with your truck's fuel system. A faulty fuel pump or failing fuel lines can potentially create runaway, so you should repair these problems as soon as you can. Repairing an engine that suffered from runaway often involves a partial rebuild (at a minimum), so fixing problems before they progress will always be the cheapest option.

Remember that runaway conditions can be both extraordinarily damaging and dangerous. By recognizing and repairing the potential causes of these problems, you'll avoid one of the most challenging and costly situations you may face on the road. For more information, contact a diesel repair company in your area.