By Charlie Haigh
Keeping your oil clean is important to the life of your vehicle. This is because it not only lubricates but also cleans and cools the moving parts. The oil transfers heat from the block to the oil pan as well as holding any dirt it picks up in suspension. The oil also gets thicker as it is used because the lighter molecules or more volatile parts of the oil get hot and turn into vapor. This combination causes the oil to transfer less heat and lubricate less.
This is where synthetic oils really start to have a benefit to the engine. Because synthetic oils don't have any variation in molecular size or volatility they don't vaporize off or get thicker. This allows the oil to lubricate better at low temperatures and as the oil gets dirtier. The synthetic oils also have less problem with viscosity break down at higher temperatures because of their stability.
Regardless of what type of oil you use, you should change it and the filter regularly, using a good quality oil filter. This is the least expensive long term maintenance you can do for your Land Rover.