…specifically people running Rover V8's and other older engines. Snazzy modern oils are designed for snazzy modern engines with tight tolerances, tiny bearings, and carefully designed cooling and lubrication systems, these oils will do your engine no good at all and may harm it.

Older Rover V8's (pre-Range Rover P38-era) were designed to run on nice thick oil at relatively low pressure, and as such all the bits in the engine are designed with this in mind - from the oil pump to the big end clearances. Putting £100 worth of 0W30 Mobil 1 into an old V8 is most likely to lead to the oil pump being unable to even suck it out of the sump, never mind push it around the engine without it all just running out of the gaps like water. I know this because I made the mistake myself many years ago - I lost oil pressure whilst off-roading and the system just couldn't re-prime itself with the hot, runny synthetic oil.

Even P38-era don't really want very thin oil, although they do have a better oil pump and the manual specs lower viscosity oil than the older type engines.

What you need is…

The Rover V8 is a simple old hector - the advice is always to buy reasonable quality, cheap 20w50 or 15W40 and filters in bulk, change both regularly and your V8 will be far happier than long intervals on posh oil.

For comparison, here's the official oil specs for the modern BMW M47 engine, known as the TD4 in the Freelander 1:

And here's the same for the Range Rover P38 with its big dumb old Rover V8:

And here's a handy chart I found on the internet: