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.

 

Live in Wisconsin, USA but only drive my XJ6C S2 in warm weather. Using 20W50 Castrol GTX, but thinking of switching to Mobil 1 20W50. Thoughts from experienced owners appreciated.

 

I used 15W40 in my 1980 XJ6, and this was the recommended oil as I recall. When the XK engine came out in 1948, it was produced on secondhand machinery bought from the Standard Motor Company. Originally used to make the pushrod engines it carried on in use almost for ever !! There was a high degree of selective assembly in the production. The recommended olils and the change interval gradually changed over the years as oils improved, and also, don't forget, the oil filters. If I were still running that XJ (sold in 2002), I'd be using the 15W40 today. I don't think it's a good idea to move drastically away from original specs, unless, of course the spec is no longer available.

 

I would use the lowest first number you can get, and the second number use whatever the manufacturer recommends. Often that turns out to be a 0W-30 or 0W40.

The reason for the 0 is that is the cold viscosity which is present at startup. You want the oil to flow as fast as possible, as around 90% of engine wear occurs at startup because there is minimal lubrication. So get the oil up into the engine as fast as possible. The second number is the hot viscosity, match that to what is reccomended.

Note that the two numbers are measured at different temperatures, so the actual viscosity is different. at their measured conditions, a 40W hot is actually a lower viscosity than a 0W cold. For example, for a 0W it's viscosity at 40° is 80 cSt, and a 40W at 100°C it is 15 cSt.

 

I use Castrol Classic 20/50

Jeff H.