Spark plugs
Spark plugs are constantly subjected to extensive operation and exposed to very high temperatures. As such, their efficiency and spark intensity gradually weaken. In general, normal spark plugs (not platinum plugs) should be replaced every 40,000km.

By replacing the spark plug at the recommended mileage, the spark plug's efficiency is sustained and this provides good fuel economy. Faulty spark plugs may result in engine misfiring and jerky drive feel.

Automatic transmission fluid (ATF-Diaqueen SP III)
An automatic transmission provides comfort and minimises stress to the driver. By the time the vehicle has covered 40,000km, the condition of the ATF would have deteriorated and it needs to be drained. This happens as a result of the multiple engagement and disengagement that took place during the 40,000km coverage.

When the transmission is subjected to frequent overloading and uphill driving, the ATF is easily heated up and becomes thinner. Another situation where the ATF is likely to heat up is when the selector lever is left in D position in a bad traffic jam or in a prolonged stop-and-go situation. In the above conditions, the ATF temperature around the torque converter tends to rise since the turbine is held at most of the time while the impellor is rotating at the same speed as the engine.

In such situations, the ATF is thinner and the protection they provide to the brakes and clutches become insufficient. When the transmission is subjected to this kind of environment continuously, there will be an increase in the wear-and-tear of the transmission parts.

In some cases, the colour of the ATF may indicate that it has degraded. In these cases, even if the mileage covered is below 40,000km, it is advisable to replace the ATF to restore the ATF's performance. Thus, a regular ATF change will enable the transmission to go a long way.