High mileage spec oils - yay or nay?

[Green Whale]

I've been told by a friend who deals in vintage cars that oils such as Castrol GTX 15w 40 and other classic car higher viscosity oils are preferable for vehicles over a certain age or mileage.

I was wondering if anyone on here deviates from the normal manufacturers spec and what experiences they've had?

[jamesy12345]

20W/50 valvoline in my OHV renault 5, any decent 10W/40 in RX7 & S70.....mineral oil in the Mazda & semi-synthetic in the Volvo if I'm feeling rich. S70 has hydraulic tappets & no VVT so I guess that is just about the same as an 850...I try to follow manufacturer's recommendations unless good evidence to deviate

[500tie]

Have to agree with jamesy on this one, I always go by the manufacturer recommendations unless there is good evidence to prove otherwise.

[Green Whale]

Fair enough.

I suppose the logic with the Castrol 15w 40 is it's slightly thicker so will give a better pressure on high mileage engines where wear has increased tolerances etc.

I'll stick with 10w 40 semi synth for now then.

[martin_r_smith]

I use shell helix ultra 5w40 (great deal with opie) in my 210k diesel, It's a good price and the oil performs very well.

[jamesy12345]

I think unless it's burning/leaking loads of oil nothing to worry about. 10W/40 and 15W/40 is the same viscosity anyway when the engine is hot