The answer is the same as why you should brush your teeth every day!
Let’s be honest, none of us enjoy getting out car serviced, brushing our teeth isn’t very fun either, but we still need to do it. If we don’t brush our teeth eventually your teeth will start to gum up and break down, this will always lead to further damage. Oil over time oil will also break down, deteriorate and gum up and become less efficient at providing good lubrication and protection for your engine. The chemical compound of oils these days serve and protect to a high standard, but deteriorate just as quick at the end of their life.
So how often should I change my oil? Most vehicle manufacturers have a recommended service period either based on kilometres travelled or a specific time period. Rule of thumb is normally every 10-15 thousand km’s or every 6months whichever one comes first.
Theses are the two main reasons to have your oil changed every 10,000kms or 6 months, whatever comes first.
1. To remove the contaminants that degrades the oil such as:
a) Moisture (condensation).
b) Un-burnt fuel (fuel dilution).
c) Soot (by product of combustion, especially in diesels).
d) Oxidation and Nitration By-products such as acids.
2. To refresh the oil, as additives in the oil deteriorate over time, for example:
a) Detergents that help keep the engine clean become less effective.
b) Dispersants, that hold contaminants in the oil become saturated and can no longer retain contaminants.
c) Anti-wear additives need to be replaced such as ZINC which is sacrificial.
d) VI Improvers are sheared by the engine and hence oil loses its viscosity lowering operating protection.
The cheapest thing most people will ever do to keep their vehicle running and lasting the distance will be to change the oil and filter on a regular service basis.