oil compatability?

[mickey]

gonna do the oil change in the morning,been running on gtd magnatec 10/40,i'm assuming its a synthetic brew?...anyways,although i dont begrudge the beast a healthy drink,i cant help but wonder if i aint shovelling diamonds on a coal fire?...it seems a semi-synthetic 10/40 would be as suitable,but more economical?...i am a little wary though,regarding the inter-changeability,ie,there will be traces of the old stuff in the system,does semi and fully synthetics mix?...i'm paying £21.00 for 4.5 litres of the stuff.looking at the other castrol in the black container,i cant remember if it said suitable for turbo diesels,whereas the magnatec i've been using definatly does.

[Gamedawn]

I think most people tend to use semi-synthetic. I use Comma 10-40 Semi and change it and the filter at least every 4500 miles. In my opinion fully synthetic is only really necessary in highly stressed engines.