lanmjdun's right the engine was never designed to use synthetic or semisynthetic recommended oil is mineral I use ASDA 5.99 for 4.5 litres change oil and filter every 5,000 miles. Currently run 3 range rovers 1993 3.9 classic, 2000 4.6 and 2001 4.0. all converted to dual fuel (LPG/gasoline)...