I decided to give the Shell oil a go. I haven't tried fully synth in my truck yet, so a drum of the stuff should be enough to be able to tell whether it makes any difference over semi-synth. I have seen that when I used Toyota oil it burned a bit of oil between changes (this was last winter). The Castrol Magnatec didn't seem to need an top ups between changes, until the weather started getting colder..? The Shell is 5W-40 rather than 10W-40 so should help a bit with cold starting (if my understanding of viscosity ratings is correct...).