Which oil are people using in their CDTI's, I looked at Mobil 1 but with service intervals of 15K I'm not running the car 24/7 in extreme temperatures for 25K miles therefore seems costly opposed to other fully synthetic oils.
Suppose Im always looking for value for money in my motoring.
For me I think splashing out on brand names and buying fully synthectic oils is not necessary.
I think if you stick with the viscosity rating as recommended for your car and check the oil specs listed on the container and understand what they mean,you will find many better priced oils are more than a match for brand names.
If your car is specified fully synthectic only than go with it,but I would have thought this is more to do with extended service intervals and initial warranty for newer cars.
I would use a good spec sensible price oil either mineral or semi synthectic and change oil once or maybe twice a year.
Also if your cars older and leaks abit of oil or uses oil these fully synth oils become even more expensive.