Why Does the Engine Shake When the Cooling Fan is Running?
3 Answers
When the cooling fan is running, the engine shaking phenomenon occurs due to a dirty throttle body. The following is an introduction to the throttle body: Function: The throttle body is a controllable valve that regulates the air entering the engine. After the air enters the intake pipe, it mixes with gasoline to form a combustible mixture, which then burns to generate power. It connects to the air filter at the top and the engine block at the bottom, and is referred to as the throat of the car engine. Classification: The throttle body is one of the most critical components in today's fuel-injected engine systems. There are two types of throttle bodies: the traditional cable-operated type and the electronic throttle type. In traditional engines, the throttle control mechanism operates via a cable or rod connected at one end to the accelerator pedal and at the other end to the throttle linkage plate. The electronic throttle primarily uses a throttle position sensor to adjust the throttle opening angle based on the engine's energy requirements, thereby regulating the amount of air intake.
I remember encountering a similar situation during my last car repair—when the cooling fan kicked in, the engine shook violently. There could be several reasons: an unbalanced fan transmitting vibrations to the engine block, or the fan's high power draw upon startup causing voltage fluctuations that interfere with the ignition system. Sometimes, damaged or loose fan blades directly induce engine vibrations. Additionally, worn engine mounts may fail to absorb the extra vibrations. This issue is particularly annoying—I've experienced it multiple times during summer road trips, where the car would slightly wobble when the fan activated, most noticeably at idle during red lights. It's crucial to promptly check if the fan mounting screws are tight, clean dust and debris from the blades, or have a professional shop test for abnormal signals in the engine control unit. Long-term neglect could escalate into more severe problems.
When driving, I feel the engine starts to shake as soon as the cooling fan kicks in, such as when the air conditioning is fully on and the fan spins at high speed. I think it's mainly related to the increased load from the fan. When the fan starts, it draws some power away from the engine, especially noticeable in smaller displacement vehicles, causing a momentary drop and fluctuation in RPM. Another common issue is electrical interference; the fan motor generates electromagnetic fluctuations that interfere with the spark plug ignition, leading to unstable operation in some cylinders. In older cars, worn-out fan bearings can produce abnormal noises along with vibrations. I experienced this last year during hot weather—when the fan was running, the steering wheel would slightly tremble, and it improved when stationary. It's advisable to regularly clean the engine bay to prevent excessive dust buildup. Promptly check the balance and mounting of the fan assembly, and replace or repair it if necessary to avoid potential hazards.
