Pressing forward: The hidden dangers of skipping downshifts
Drivers sometimes make a basic mistake: they press the gas pedal hard during acceleration without first changing gears. This may stem from a lack of knowledge, inattention, or laziness. Such a practice fails to produce the desired results and can damage the engine. Here's why.
When learning to drive, we're taught that downshifting is essential before overtaking. Switching to a lower gear offers greater power and engine torque, resulting in better and more dynamic acceleration. Modern turbocharged engines produce significant torque at low RPMs, and when road conditions permit, drivers often skip downshifting, which is a mistake.
This method of accelerating takes longer and causes more energy loss in the form of heat. Worse still, companies like Toyota and Denso have found that it can lead to premature ignition. This means the fuel mixture ignites before the piston fully compresses it. How does this happen?
This is a typical situation of high engine load with insufficient power. Without the appropriate torque, the engine tries to "rescue" itself by adjusting the injection parameters. It increases the fuel dose because it's the only way to generate higher power, especially at low RPMs.
Adding fuel to the fire
Excess fuel makes the mixture rich, making it impossible to burn completely. The engine experiences an unexpected power surge, causing significant strain on friction nodes and potentially leading to the breakdown of the oil film. It's like fueling the fire; while the benefits are temporary, the consequences worsen the situation over time.
Excess fuel also has other effects. Residual unburned fuel reaches the crankcase through the cylinder walls, where it mixes with the oil. Vapours of these substances reach the breather and then return to the combustion chambers along with gases from the crankcase.
In such a scenario, residual oil and fuel accumulate in the combustion chamber, which is flammable and not properly removed with the exhaust gases. This causes the mixture to ignite before the spark plug initiates it in subsequent compression cycles, completely automatically. This leads to uncontrolled micro-explosions, which deliver a powerful "blow" to the pistons, connecting rods and bearings on the crankshaft.
Toyota and Denso have confirmed that the higher the engine RPM, the lower the risk of premature ignition. The article below explains this mechanism in more detail.
Premature ignition can be extremely harmful. The engine is then exposed to enormous forces, which, in the best-case scenario, lead to wear of the spark plugs. In the worst case, it can result in cracked pistons, bent connecting rods, and the need for a major engine overhaul. Moreover, the more the auto-ignition phenomenon intensifies, the more frequently it occurs over time.
