许多人在刚购买新车时会发现，油耗相对较低，足以成为炫耀的资本。然而，随着车辆使用年限的增长和行驶里程的累积，油耗逐渐攀升。一辆原本每百公里耗油7升的汽车可能增至8升甚至9升。这究竟是何原因？许多人认为这是车辆老化的正常现象，因此并不采取任何检查或维修措施。然而，车辆老化只是其中一小部分原因，最主要的还是因为保养不当。以下是四个常见原因：

1. The air filter has not been replaced for a long time

Many people focus on oil changes and neglect other maintenance aspects, such as air cleaners. Some experienced drivers may inspect the filter and if it doesn't look too dirty, they will simply reinstall it and rarely replace it. In fact, modern air cleaners filter well and absorb most of the dirt. Although it may not seem dirty on the surface, it may be blocked on the inside.

当空气滤芯变脏时，会影响空气流通，减少进入气缸的空气量。这将导致燃油和空气的混合比例失衡，使混合气过浓。结果是燃烧不完全，动力降低。只要燃烧不完全，就说明汽油的能量没有完全释放，从而导致油耗增加。据数据显示，当空气滤芯阻塞时，油耗可增加10%-15%。原本每百公里耗油7升的汽车，受此影响可能增至8升。我们可以将空气滤芯比作口罩，如果口罩上积满灰尘并阻塞，我们的呼吸将会不畅。缺乏足够的氧气可能导致头晕眼花等问题。

2. The tire pressure is too low

骑自行车的人都知道，如果车胎气压不足，骑行将变得十分困难，尤其是在上坡时。而充足气的自行车会感觉更轻便，平路上骑行也不费力。汽车也是同样的道理，如果胎压过低，轮胎与地面的接触面积增大，摩擦力变大，行驶阻力也随之增加。为了克服这种增加的摩擦力，车辆需要消耗更多的燃油。有数据表明，如果胎压低于标准胎压的30%，每百公里油耗将上升1-2升。胎压越低，油耗越高。仅胎压一项，就可能使每百公里油耗增加2升，足以看出其对油耗的影响之大。

3. Vehicle carbon deposits

对于燃油车来说，积碳问题是不可避免的，只是产生的速度快慢不同。有些车辆两万公里就积累大量积碳，而有些六万公里才出现。这与驾驶习惯和路况有很大关系。积碳可能出现在节气门、进气道、喷油嘴和活塞顶部等处。节气门积碳会影响进气效率和时机，导致进气量减少。喷油嘴积碳则会导致喷出的汽油雾化不良，甚至喷油量不足。车辆一旦积碳，最终都会导致燃烧不完全或时机不准确，从而浪费能量。这样，行驶相同距离就需要更多燃油，油耗自然增加。

4. The spark plug has not been replaced for a long time

Spark plugs are an accessory that is often overlooked. Some experienced drivers believe that as long as the vehicle is running smoothly and there is no jitter or lack of power, there is no need to replace the spark plug. However, as the mileage increases, the ignition capacity of the spark plug gradually decreases. When the ignition ability is weakened, it will lead to a deviation in the ignition timing. The mixture, which was supposed to be ignited immediately, was now postponed due to lack of energy. The mixture is ignited only when the piston has already started to descend, resulting in the inability to maximize the use of the energy generated by combustion to push the piston forward, resulting in wasted energy and increased fuel consumption. The manufacturer's maintenance manual also clearly indicates the replacement cycle of the spark plug, which should be replaced in time after reaching a certain mileage.

The above four points are the most common causes of high fuel consumption, and they are also the most easily ignored problems by car owners. Therefore, when an old car has high fuel consumption, these four basic and most likely problems should be checked first. If there is no improvement, other further tests are done.