Changed my 12000 mile old oil (standard change time for a CRD). Put in 5w 40 Castrol EDGE.....usually use a 10w 40 semi synthetic but Castrols website advised a fully synthetic 5 w 40 for max protection for my engine. The choice was obviously nothing to do with being able to get it cheap!!....well maybe a little. Being a diesel the old oil was very black....usually is after a very short time to be honest. Used STP engine flush and left the sump to drain overnight. I like to do that to get as much oil stuff out as possible and I never put cold new oil into a hot engine anyway so it allows the motor to cool right down. Fitted a new WIX filter (cheapest on Ebay too!) Added my usual bottle and a half of XIR as well.....not for any claimed performance gain but as protection for my engine on cold starts and if the engine should suffer a major failure (oil pump etc) it give it half a chance of stopping it before any serious damage. The company has quite a good video of them flying a small plain with an empty sump....just relying on the X1R for protection! Im not saying whether it really works or not but its never caused my motors any harm so why not?
I have noticed (probably due to the 5w oil) that it turns over quicker from cold and picks up revs faster....feels like a warm engine from the off. The whole car just feels smoother. Hope it lasts. The only downside is that it has slightly lower oil pressure when hot and idling....but not so low to worry about.