Not changing car engine oil for a long time can lead to multiple negative effects. First, the lubrication function decreases significantly. After the oil deteriorates, it cannot form an effective oil film on the surface of metal engine components, which intensifies the friction and wear of precision parts such as pistons and cylinders, thereby shortening the engine's service life. Oxidized and deteriorated oil has reduced thermal conductivity, which may cause the engine to overheat, leading to a drop in power or abnormal vibration. In severe cases, it can cause engine failure, with repair costs possibly reaching thousands or even tens of thousands of ringgit. The loss of the oil's sealing performance will also lead to insufficient cylinder pressure and incomplete fuel combustion, increasing fuel consumption by 10%-15%. To determine whether the oil needs to be changed, you can observe its condition (such as turning black, abnormal viscosity, or having an acidic odor), but it is more recommended to follow the cycle standards in the manufacturer's maintenance manual: mineral oil is usually changed every 5,000 kilometres, semi-synthetic oil every 7,500 kilometres, and fully synthetic oil can last up to 10,000 kilometres. Even if the mileage is not reached, the oil that has been opened will expire due to oxidation within 6-12 months, so it needs to be replaced regularly to ensure the engine's optimal performance.
