How Many Minutes Does It Take to Clear Carbon Deposits by High-Speed Driving?
4 Answers
On the highway, use an appropriate gear to keep the engine running above 3500 RPM for a certain period, such as driving at 110 km/h in 3rd gear or 140 km/h in 4th gear. For automatic transmission vehicles, use the forced gear mode to prevent gear shifting, and maintain this for 15 to 20 minutes. Below are the details about clearing carbon deposits through high-speed driving: 1. Detail One: Incomplete fuel combustion produces various substances, such as gums and carbon particles. However, the primary byproducts of fuel combustion are water vapor and carbon dioxide, and combustion also requires a significant amount of air. The car's air filter meets the ≥PM2.5 standard, but the air entering the engine still contains some impurities. 2. Detail Two: Every cold start of a car generates carbon deposits during the warm-up process. During operation, the engine reaches very high temperatures, causing the gums to harden under high heat and their adhesion to increase significantly. At this stage, carbon deposits become as stubborn as "sticking plaster" and are difficult to remove. More importantly, they accumulate over time.
I've been running an auto repair shop for twelve years, and this question comes up often. Clearing carbon deposits by high-speed driving isn't about timing—it depends on engine conditions. For small-displacement cars to burn off deposits behind valves, you need at least half an hour of sustained driving. Keep the throttle at around 4000 RPM to raise exhaust temperatures enough to burn off carbon buildup. The key is maintaining high-RPM driving without stop-and-go. But I often tell customers, with today's direct injection engines, carbon mainly builds up behind intake valves where high-speed driving has little effect—walnut shell blasting is still needed. If you hear engine knocking on the road, it means carbon deposits are too stubborn and require professional treatment.
Last year, my car's malfunction light came on, and the 4S shop said there was too much carbon buildup, suggesting I take it on the highway. I tried driving at 80 km/h in third gear on the ring road for a full 40 minutes, but the fuel consumption skyrocketed to 15 liters per 100 km. Later, I asked an engineer friend and learned that driving at high speeds has minimal effect on intake valve carbon deposits in direct injection engines and can even damage the catalytic converter. Their factory conducted tests showing that running at 4000 rpm for 20 minutes can remove surface carbon deposits on the piston top, but stubborn carbon layers require soaking with fuel additives. Now, I use PEA-based additives, adding one bottle per tank to slowly dissolve the deposits, which is much safer.
Veterans in the tuning scene know that carbon cleaning varies by model. Naturally aspirated engines do benefit from highway runs, but you need to maintain near-redline RPM for 15 minutes. When I drove a manual Fit, I'd do five-minute overpass runs in second gear at 5,000 RPM weekly - kept the throttle body spotless. But never try this with GPF-equipped new cars, you'll clog the particulate filter. A colleague's Civic ruined its GPF this way, costing over 8,000 RMB in repairs. The safest method is using diagnostic tools to monitor air-fuel ratio - highway pulls only work when the mixture is too rich, otherwise it's just wasted fuel.
