The winter season is behind us. For several months, motorists have been navigating snowy yards, enduring lengthy morning traffic jams daily, and warming up their cars for extended periods using remote start. With the arrival of spring, as roads dry out and the opportunity to hit the highway arises, many suddenly notice changes: the car has become less responsive, dynamics have deteriorated, and fuel consumption seems to be stuck at winter levels.
In such cases, a familiar piece of advice from experienced garage neighbors often surfaces: the engine, they say, has become "coked up" in traffic and needs to "breathe" on the highway—to be given a load so that the valves can be cleaned. Some drivers are skeptical of such recommendations, considering them a relic of the past and preferring to pour specialized automotive chemicals into the tank. However, engine specialists confirm that there is indeed a real physical process underlying this advice, although it is implemented differently in modern engines than before. It is important to understand why the engine needs such a load and how to perform the procedure without harming the unit.
The reason lies in the design features of modern injection systems. In older engines with distributed injection (MPI), the injectors were located in the intake manifold. Fuel was supplied directly to the intake valves, performing not only the function of supply but also the role of a solvent—it constantly washed the valves, preventing the accumulation of contaminants.
In modern power units, including German TSIs, Korean GDIs, SkyActiv family engines, and the vast majority of Chinese turbo engines, direct injection is used. Here, the injector is already installed in the combustion chamber. As a result, the intake valves are completely deprived of contact with gasoline—the fuel does not clean them.
However, other substances settle on their surface. Oil mist enters the intake through the crankcase ventilation system, and soot particles enter through the exhaust gas recirculation system. In winter, when the engine often runs at idle and with an enriched mixture, this mixture actively accumulates on the valves. Over time, a dense layer of carbon deposits forms, which narrows the air channels. As a result, the filling of the cylinders deteriorates, and the engine literally begins to experience a shortage of air.
A logical question arises: if gasoline no longer cleans the valves, how does driving at high revs help? The answer is related to thermodynamic processes. During calm city driving at low revs—around 1500–2000 rpm—the temperature in the intake system remains insufficient to break down deposits. The carbon deposits only become denser and turn into hard coke.
A different situation arises with prolonged load on the highway. At increased revs, the temperature of the exhaust gases and the heating of the valves themselves increase significantly. When the temperature reaches a range of approximately 350–400 °C, the accumulated oil-soot layer begins to burn out and break down. Particles of exfoliated carbon deposits are removed along with the exhaust gases. Thus, there is no "gasoline flushing"—the engine is actually cleaned due to the high-temperature regime, similar to the self-cleaning function in a household oven.
However, it is important to understand how to perform this procedure correctly. A common misconception is that you just need to accelerate to a high speed. In practice, speed is not the key factor—engine revs and the load created are important.
The optimal algorithm is as follows. It is necessary to choose a free section of the highway, switch the automatic transmission to manual mode, and fix the gear—usually third or fourth. Then, you should drive at the permitted speed of about 90–100 km/h, maintaining engine revs in the range of 3500–4500 rpm. In this mode, you need to spend at least 15–20 minutes, which corresponds to approximately 20–30 kilometers of travel. During this time, the engine reaches the required temperature regime: the spark plugs are cleaned of deposits, part of the carbon deposits in the combustion chamber burns out, and the catalytic converter warms up to an effective temperature.
At the same time, there is an important limitation that cannot be ignored. Performing such a load on worn or used engine oil is extremely dangerous. In winter, a significant amount of unburned fuel and moisture enters the oil due to frequent cold starts. As a result, it thins out and loses its protective properties. If you subject the engine to high revs in this state of lubrication, the oil film may break down, which will lead to serious damage, up to and including the turning of the crankshaft bearings.