What Are the Hazards of Long-Term Engine Idling?

[AmirLynn]

The hazards of long-term engine idling include: 1. Wasting fuel, which is the most direct impact; 2. Generating a certain amount of carbon deposits. Due to the low engine speed and low air intake efficiency during idling, combustion is not very complete, making it prone to carbon deposits. More importantly, the carbon deposits produced cannot be expelled and will continuously accumulate in the cylinders and intake passages, significantly accelerating the rate of carbon buildup. Idling refers to an operating state of the engine, generally when the throttle is completely released, and the engine runs naturally. Simply put, it is the operating state when no throttle is applied. The idle speed varies for each vehicle, and even for the same vehicle, the idle speed differs between cold and warm conditions. The idle speed is much higher when the engine is cold, which is controlled by the engine computer to achieve a high idle speed during cold starts. The purpose is to rapidly increase the water temperature to reach the normal operating temperature, reduce engine wear, and minimize harmful exhaust emissions.

[MacTanner]

I used to frequently let the engine idle while driving, especially in traffic jams or while waiting for someone, and found it quite harmful. First, fuel consumption increased significantly—the engine was running but the car wasn't moving, wasting fuel. My monthly fuel expenses were hundreds more than usual. Second, carbon deposits easily formed. Long-term low-speed operation led to incomplete combustion, causing residue buildup in the cylinders and on the fuel injectors, which several times resulted in engine shaking and reduced power. I also noticed insufficient lubrication, as the oil circulated slowly, accelerating wear on components like piston rings and bearings. A mechanic once told me this could lead to an earlier need for major repairs. Additionally, cooling was inadequate—staying at high temperatures for too long with poor fan efficiency once nearly caused overheating and a breakdown. Overall, developing the habit of turning off the engine during short stops can protect the engine and save money.

[Xavier]

I am concerned about environmental and practical issues, and prolonged idling poses multiple hazards. It emits large amounts of pollutants, with incomplete combustion generating more hydrocarbons, carbon monoxide, and nitrogen oxides, which pollute the air and affect atmospheric quality. I learned online that this not only exacerbates urban smog but also leads to clogged emission systems and frequent check engine light warnings. Increased fuel consumption also wastes resources—a fuel-efficient car idling for an hour may use an extra half-liter of fuel, inadvertently raising expenses. Low thermal efficiency affects overall performance, and carbon buildup on valves and throttle bodies can cause cold-start difficulties and unstable idling. It is advisable to periodically check the air filter or use additives to mitigate the impact, but avoiding prolonged idling is best.

[DiJuniper]

As a DIY car enthusiast, prolonged idling can cause significant damage to the engine internals. Friction between engine components increases, especially between cylinder walls and piston rings, with accelerated wear potentially leading to decreased cylinder pressure and oil leaks. Carbon buildup is a major headache – deposits on spark plugs and intake manifolds can easily cause ignition failures or rough idling. I've personally experienced battery drain issues where the alternator's slow rotation fails to provide sufficient charge, affecting the start-stop system too. Additionally, incomplete combustion reduces fuel efficiency, worsens vehicle condition, and sends maintenance costs soaring. Regular fuel injector cleaning and sensor checks can help mitigate these issues.