Synthetic base oils have a number of advantages over mineral base oils. The uniformity of the synthetic oil molecules improves the thermal stability and reduces oxidation of the oil. Controlled molecular structure also results in lower volatility and a more stable vicosity over the life of the oil.

Most diesel engine oils carry a higher specification rating than petrol engine oils and vehicle manufacturers often specify a diesel engine oil be used in a petrol motor. This does not work in the reverse, petrol only engine oils cannot be used in diesels. Some engine oils carry both petrol and diesel specifications.

Tap water quality can vary widley depending on your location. It is best to use deminalised or deionised water, as tap water contains chemicals and minerals which can effect the performance of the coolant.

The main drive behind the use of thinner engine oils is fuel efficiency. The thinner the oil the less drag on internal components and also results in reduced energy loss caused by the oil pump etc.

All engine oils contain detergent and dispersant additives which remove contaminant build-up inside your engine. When new oil is added to an engine these additives strip away build-up and hold the contaminant in suspension so it can be removed when the oil is drained, this does discolour the oil.