Typical reasons for Oil Loss & Consumption

An engine needs oil for a long and healthy life. However, we tend to worry less about the importance of regular oil level checks. The question of oil consumption tends to take us by suprise, and usually only arises when the dipstick comes out dry "again".

Oil Dipstick

Before we can start to look for the reasons behind the loss of oil, it is first necessary to define various terms in more detail. Normally, the term "oil consumption" is always used in a very general sense. However, in the workshop it is necessary to make a distinction between the loss of oil and the actual oil consumption.

A specialist only uses the term "oil consumption" to describe the quantity of oil which enters into the combustion chamber where it is then burned or coked. The term "oil loss" is used to cover all of the oil lost through leakage throughout the entire engine.

It can be difficult to differentiate between oil leak and oil consumption if no oil spots are found on the ground under the engine. Engine leaks may only occur when engine is running or at speed.

Bigger oil leaks are always visible when looking at the engine from below. Engine components will be covered in oil and dirt. Oil leaks always go downwards and backwards, so tracing of the oil leak is done by going upward and forward until engine components are found clean and dry.

Oil consumption can be identified by looking at the spark. A good spark combined with a good combustion will result in a light brown or a greyish/white tip. A black & ashy or a wet with oil spark plug tip (and the last few spark plug threads) is proof of oil entering the combustion chamber and burning.

Primary reasons for oil loss:

1. Leaking oil seals (sealant between two mating surfaces)

2. Leaking oil radial seals (on a rotating shaft)

3. High oil pressure

Primary reasons for oil consumption:

1. Poor engine maintenance

2. Fuel injection pump (diesel engine)

However, even on modern engines a certain level of oil consumption (not oil loss) is acceptable. Typical values for acceptable oil consumption are (manufacturer's specifications may vary)

1. High load engines, such as truck engines: 1-3 litres of oil consumption for every 1000 km
2. Medium load engines, such as car engines:
   • Engines with up to 2 litres of oil: 0.5-1 litres of oil consumption for every 1000 km
   • Engines with more than 2 litres of oil: 0.5-1.5 litres of oil consumption for every 1000 km