What Causes Low Engine Load?
3 Answers
Low engine load occurs when the throttle opening is small, resulting in reduced air intake and an increased proportion of residual exhaust gases in the cylinders. The carburetor needs to supply a richer air-fuel mixture for combustion, while the power consumed in overcoming engine friction resistance and driving mechanical components increases proportionally. The fundamental requirements for driving technique are: To keep the engine operating at the most fuel-efficient RPM as often as possible, drivers should appropriately utilize coasting, control vehicle speed, apply brakes correctly, and maintain proper engine temperature and economical driving speed. The reason for increased fuel consumption rate at higher RPMs is: Greater power is consumed in overcoming mechanical friction resistance and intake/exhaust processes.
When I drive myself, I often encounter situations where the engine load is light, meaning the engine is working with less effort. The most common reason is a light vehicle load, such as driving alone with an empty car and nothing in the trunk, so the engine doesn't have to pull heavy weight. Additionally, driving habits greatly influence this. If the accelerator is pressed very gently and acceleration is gradual, the engine operates much more leisurely. During long highway trips, I've noticed that on flat roads, tire resistance is low, and with cruise control engaged, the speed remains stable without frequent acceleration, naturally reducing the load. High gear and low RPM are also key factors. For example, in a manual transmission, shifting to fifth gear at 80 km/h with the RPM at just 2000 is much easier than running at lower gears with higher RPM. Moreover, when the throttle opening is small, the intake air volume is reduced, leading to smoother combustion, and the engine sound becomes milder. Actually, a light load isn't necessarily a bad thing—it can save fuel, reduce engine wear, and benefit the vehicle's lifespan.
I've been repairing cars for over a decade and have encountered many car owners asking why their engine has a light load. Simply put, it means the engine is producing less power, and there are quite a few reasons for this. For example, when driving with the accelerator pedal pressed lightly, the fuel injection volume is reduced. If the vehicle is lightly loaded, either empty or carrying little cargo, the engine bears less burden. Environmental factors also play a role, such as driving on flat roads without the resistance of climbing hills. If the transmission is in a high gear, it's like riding a bicycle with a large gear—pedaling is easier but you move faster, resulting in lower engine RPM and reduced load. Additionally, the vehicle's design itself has an impact; modern cars have lower drag coefficients and reduced tire rolling resistance, making them more efficient to drive. Under normal driving conditions, a light load is nothing to worry about and can actually improve fuel efficiency. However, if an abnormality suddenly occurs, such as the car lurching forward with just a light press of the accelerator, it's necessary to check if the throttle position sensor is malfunctioning.
