We have met some concern about the use of synthetic oils, in that they have been attributed to causing low engine oil pressure when hot. We would like to clarify the situation. To this end, we have contacted Castrol (UK) Ltd. for their advice and this is their response:
Oil pressure is directly related to viscosity and it is therefore not the difference between synthetic and non-synthetic oils that causes the difference in pressure, more the fact that modern synthetic oils are of a lower viscosity than the A series engine was originally designed for.
Modern, new generation, engines are being designed to run on lighter viscosity oils to aid lubricant flow when cold and provide less viscous drag when hot thereby aiding fuel economy. The lubrication system in older engines is designed to cater for larger working clearances on crankshaft and camshaft bearing journals, valve gear and other moving parts, plus oil galleries will be larger and the oil pump will be of a suitable design to pump oils of a heavier viscosity irrespective of their base oil type.
Synthetic oils are designed to give greater film strength and higher levels of lubricity together with increased thermal stability and better resistance to oxidation. They are also able to maintain their properties when used under arduous or extreme conditions. These special properties also enable lighter viscosity, energy efficient oils to be used whilst offering an enhanced level of protection and performance.
Whilst the lower viscosity of some synthetic oils may lead to reduced oil pressure, it does not necessarily mean reduced protection. However, owners who are nervous of a reduction in pressure should consider using Castrol Formula RS 10W-60 which will give rapid circulation when cold but will retain a substantial viscosity when up to its full working temperature.
We would like to thank Castrol (UK) Ltd. for their kind assistance.