[JohnM 855 T5R]

Mobil 1 5W50 will be absolutely fine in your C70. My old C70 was run on Mobil 1 0W/50 (it started life at that viscosity) then 5W50 when it changed, for its whole life (400k+ miles) from new.

I refer you to another thread currently active (98 V70R oil) which discusses oils to which I have posted fuller discussion and a link to a useful document about the technical aspects of oil.

Seemingly, the main reason semi-synthetics were produced was to give an oil of superior performance over straight mineral oils at a price to consumers who were resistant to the much higher cost of full synthetics. Once you get to grips with the chemistry of full synthetics it's pretty clear that semi-synthetics are just a cost issue.

Having said that, not all cars will benefit or tolerate full synthetics - I'm talking now of pre 1970's cars where issues may occur with oil seals although if replacement seals of modern materials have been fitted then this is no longer a problem. Also, very early gearbox in sump cars like the A-series engined Mini, Austin and Morris 1100/1300, etc, do better on mineral but later ones were factory recommended to use semi-synthetics.

Regards
John



Regards
John