I just purchased a 86 XJ6. it has 110K on it. Runs great.
Anyone have any recommendations as to what motor oil to use? What weight? I am in a mild California.

 

If you just bought it and you don't know what oil was used previously, I would go with factory recommended.
There are many schools of thought on using synthetic from new but not when the engine has miles on it.
Choice is yours, but I have good luck with the factory recommendations.

 

A local mechanic recommended 20w50 Valvoline Turbo oil.
He claimed it has better additives for the valve train & cams.
Any truth or a myth?

 

I use Castrol 'high mileage' 5w30 in my 1986 sovereign, at least in the winter. Just don't put synthetic in it, or you'll likely start seeing oil leaks appear.

 

These are wonderfully old, sloppy engines. Go with a thicker oil then today's low tolerance cars. Jag Tech is right, go with the oil the previous owner used if you know what that is. If you don't, just decide on a good name brand and stick with it. The oil debate is a real can of worms and if you ask 10 people you will get 12 different answers. Go name brand and stick to the change intervals.