[Mgs] Oil viscosity for 3.5 V8 engine

[PaulHunt73]

As Hammill says the Rover V8 engine is a low pressure, high flow engine 
because of the additional places for oil to exit pressurised areas and 
get back to the sump not least the hydraulic tappets.  The pressures 
quoted are optimal if not optimistic, you can get a lot lower hot idle 
than that on older engines - barely registering on the gauge.  It 
depends on what you mean by 15W 50 being 'a bit high', the factory 
specified the same oil viscosities for the V8 as it did for the 
4-cylinder, i.e. for all temperatures above -10 C (10F) 10W 40 being the 
minimum and 20W 50 the maximum.  Because the lower viscosities do result 
in lower pressures I've always run 20W 50 in mine which is on its third 
time round the clock, albeit with a rebore and regrind a couple of years 
ago.

You can't compare it with oil for modern cars, which can cause harm in 
our engines.

PaulH.