Do You Need to Carbon Clean Your Engine?

When it comes to maintaining your car, the question of whether to carbon clean your engine often sparks debate. Scotty Kilmer, the seasoned mechanic with over 50 years of experience, breaks it down in his trademark no-nonsense style. Let’s dive into his insights to uncover the truth behind carbon cleaning and how it fits into the broader picture of car maintenance.

Why Carbon Cleaning Matters

For most vehicles, gasoline works double-duty: powering the engine and cleaning the intake valves. In traditional port-injected engines, gasoline flows through the intake manifold, cleaning the valves as it passes. But for gasoline direct injection (GDI) engines, it’s a different story. Fuel is sprayed directly into the combustion chamber, bypassing the intake valves entirely.

The result? Intake valves are left exposed to crankcase vapors and oil mist from the PCV (positive crankcase ventilation) system. Over time, this leads to carbon buildup—an issue GDI engines are notorious for.

A Case Study: The 2012 Kia Soul

To illustrate, Scotty looks at a 2012 Kia Soul with 150,000 miles. The car’s GDI system had accumulated carbon deposits on the intake valves, a common issue for vehicles with high mileage. While the owner got a good deal—a rebuilt engine at 85,000 miles for $3,000—it was time for some maintenance to keep the engine running smoothly.

Scotty’s verdict? Carbon cleaning is essential for GDI engines, especially if you want to avoid costly repairs down the line.

DIY Carbon Cleaning: What Works and What Doesn’t

Forget the Fuel Additives
One myth Scotty debunks is the idea that adding fuel cleaner to the gas tank will solve carbon buildup on a GDI engine. Since the fuel doesn’t pass over the intake valves, it simply can’t clean them.

Effective Methods
For significant buildup, walnut blasting is the go-to solution. This process uses walnut shells to blast away carbon deposits, but it’s costly and usually necessary for severe cases like some Volkswagens that can develop carbon layers up to half an inch thick.

For lighter buildup, Scotty demonstrates a DIY approach using spray cleaners. In the Kia Soul, he accessed the intake via the brake booster vacuum hose. By spraying cleaner directly into the intake while keeping the engine revved, he effectively dissolved and burned off the carbon deposits.

Monitoring the Results

Once the cleaning was complete, Scotty reset the car’s codes using a scan tool and went for a test drive. The Kia’s fuel trim data improved significantly, indicating a healthier air-fuel mixture and smoother engine operation.

Is Carbon Cleaning Worth It?

While Scotty emphasizes the importance of regular maintenance, he’s quick to remind viewers that not all cars require carbon cleaning. If you’re driving a traditional port-injected engine, the built-in cleaning action of gasoline will usually suffice.

For GDI engines, however, carbon cleaning becomes a critical part of long-term maintenance. Without it, carbon buildup can lead to reduced performance, rough idling, and even costly engine damage.

The Bigger Picture

The Kia Soul serves as a reminder of the importance of maintaining your car. Despite its second engine, the Soul continues to deliver reliable performance—proof that even budget-friendly cars can last when properly cared for.

But Scotty also keeps it real: don’t fall for marketing hype. Claims that certain cars last 200,000 miles without major issues should always be taken with a grain of salt.

Final Thoughts

Scotty’s advice is simple: maintain your car, and it will serve you well. Whether it’s carbon cleaning a GDI engine, changing your oil regularly, or addressing small issues before they snowball, consistent care is the key to longevity—even for a car like the Kia Soul.

Watch the Full Video

Want to see Scotty’s DIY carbon cleaning process in action? Check out the full video on his YouTube channel. Don’t forget to subscribe for more tips and tricks to keep your car running forever.