What Happens If You Start Your Car While It Running

Starting a car while it’s already running may sound like a harmless mistake, but it can actually lead to some serious issues with your vehicle. As a runner and a car enthusiast, I’ve always been curious about how different factors can impact the performance of both my body and my car. Let’s dive into the details of what happens when you start your car while it’s running, and why it’s something to be avoided at all costs.

What Happens Mechanically?

When you start your car while it’s already running, the starter motor engages and attempts to turn the engine over. This can cause strain on the starter components as they try to rotate an already running engine. The abrupt engagement can also cause damage to the flywheel and starter gear teeth, leading to costly repairs.

Impact on Engine

Starting a running engine can also result in an over-rev situation, potentially causing damage to the engine’s internal components. The sudden surge in RPM can lead to excessive wear on the engine, affecting its longevity and performance. In some cases, this can even result in a complete engine failure, necessitating a full replacement.

Effects on Electrical System

The electrical system of the car can also be impacted when you start the engine while it’s running. The sudden surge of power can put strain on the alternator and battery, leading to potential electrical system failures. This can ultimately lead to issues with various components that rely on the electrical system to function properly.

Personal Experience

I once made the mistake of attempting to start my car while it was already running, thinking it wouldn’t cause any harm. However, it resulted in a strange noise and a noticeable decrease in engine performance. After consulting with a mechanic, I learned about the potential damages and had to go through expensive repairs to fix the issues that arose from my mistake.


In conclusion, starting your car while it’s already running can have detrimental effects on various components of the vehicle, leading to potential damage and costly repairs. It’s crucial to be mindful and avoid this mistake to ensure the longevity and performance of your car. As a runner, I’ve learned the importance of proper maintenance and care for my body, and the same applies to my car. Taking the time to understand and avoid such mistakes is essential for a smooth and reliable driving experience.