Questions asked about oil

identify a suitable oil for one’s vehicle.
One reader indicated that his vehicle manual showed at least five grades of oil to use, which left him confused and to add on to the confusion the same manual indicated places in Europe and other countries.
These were SAE 5W30, 10W40, 10W30 and 20W40. This was for a diesel engine.
His mechanic however recommended 15W40, which does not appear on the list, so hence his request for clarification.
Our advice was that there is need to know the part played by temperature in the engine as it determines the type of oil to use.
Oils are classified into two ranges firstly, being for cold temperatures with a number before the letter “W” e.g. 0W, 5W, 10W, 15W, 20W and 25W. Those that show a number first then followed by W and the last numbers refers to multigrade oils.
These are called low temperature grades with an interval of 5. Secondly for countries such as Zimbabwe which have high temperatures there is need to use 20, 30, 40, 50 and 60 respectively.
However, we are of the opinion that 50 and 60 are more suitable to gear oils than engine oils as these are high temperature ranges.
The oils for cold temperature are known as monogrades indicating that they only work within one temperature range.
Generally the oil change for such oil is 5 000 kilometres. If the vehicle is constantly driven on dusty roads or short distances daily or under cold weather the oil change should at least be at 2 500 kilometres and this should include oil filter change.
Oil is required to lubricate all moving parts hence in the case of the monogrades it takes time for the oil to travel from the sump to travel up to the top of the piston in time to enable less friction between the moving parts.
Given the above this type of oil does not work well in high temperature engines.
However, about 25 years ago multigrade oils that had both features of the cold and hot temperatures were manufactured.
This type of oil works well at start up on cold weather as the oil travels very fast resulting in less friction. This type of oil is graded as 5W40, 10W40, 15W40, 15W50, 20W40, 20W50. The first figure(s) has the same effect as a monograde of 5AE 40 in that it can operate at the same temperature of minus 10 degrees.
The second letter denotes winter however it is accepted as a multigrade and three, the last figure of 40 means it can operate at a high temperature when that changes meaning has a twin effect.
Generally most wear and tear occur when starting the car in the morning hence this type of oil will react fast hence no major friction resulting in wear and tear.
These low temperature such as 0W which operates at -30 degrees, 5W at a temperature range of -25 degrees, yet 10W40 starts at -20 degrees to +40 degrees, 15W40 starts at -15 degrees to + 40 degrees.
20W40 starts at -10 degrees to +50 degrees almost equal to 15W40 and 25W at -5degrees.
20W50 starts the same with 20W40 but goes on to +50 degrees. Now to address the specific request of the reader, because our temperature range in Zimbabwe is almost uniform take the following principle of elimination to decide on what oil to use.
Generally any oil that operates above minus degrees is accepted. Hence 15W40 generally is the most popular range in Zimbabwe.
That is a tit bit which you can use to determine what oil to use. Let’s met again next week for more tit bits from Obel.