The car has 115,000 miles. Engine is a little noise idling. Lifter or some other rpm related mechanical noise.
Did the oil change today. Have been using Castrol 0-w40 European oil because two other of our vehicles spec the VW European oil. Have switched from Pennzoil synthetic to Rotella gas truck oil in two of our other vehicles. Quieten down engine noise in a Sequoia and F150. Both use 0-w20.
Well, tried the Rotella gas truck synthetic in the XJR. Used the specified 5-w30.
It was quieter after 30 seconds of running. Drove it about 10 miles and restarted. Definitely quieter on start up.
Give this Rotella for gasoline engines a try. It is like Shell claims. Best oil they make. Big improvement over the natural gas derived Pennzoil and the West German manufactured Castrol.

 

Havent seen any W. German products since the late 80s.

 

Have used the Shell Rotella 20w50 diesel oil in my bikes for years.
Diesel oil is said to have more anti wear ingredients in it.
In mine as well as many bikes, the motor oil, is also used for the trans.
Shearing the molecules in the gears, so its said.

 

I'd be inclined to say that the improvement wasn't so much to do with the make of oil but more simply because you changed the grade of oil from a 0W- to a 5W- oil which is thicker when cold. I don't think you should be using a 0W- oil unless you live where the winters are very cold, ie not Texas.

 

The Castrol Edge 0-w40 Euro oil was made in Germany until about 3 years ago. Now it lists Belgium as country of manufacture. I buy by the case.
It did not say W. Germany. Some things are hard to let go of.