Lubricants.

The largest amount of lubricants must be lubricants (engine oil). Even if a family car is not used, it must be maintained at least two to four times a year. The lubricant must be replaced, and the amount used each time is about 4 liters. For example, there are 5.6 million cars in Beijing, and the annual lubricant consumption exceeds 40,000 tons. There are 230 million cars in the country, and this number is even more amazing. The oil filter must also be replaced every time the maintenance is carried out, but because it is a low-cost product, the profit value is not high (the air filter can be replaced every two maintenances depending on the degree of use, and the air conditioning filter is preferably replaced twice a year).