Apart from extended servicing intervals to reduce on paper the T.C.O (mainly aimed at fleet buyers I guess), the thing that I feel is
potentially overlooked with say engines that have 12-18K oil intervals compared to say 6-9K is the fact the manufacturer may specify a specific oil or a specific type. By this I mean a "low ash" type expensive oil.
I've
not done the sums with this but using regular (decent) semi synth compared to uber expensive 'low ash' fully synth oil, it *may* be cheaper to change it twice as often with the cheaper oil.
Although its not exactly 'on topic' with this thread, you may recall when PSA went from 6K to 9K for diesel units and I think 9K to 12K for petrol. The only real change was the filter type at least as far as I could tell . Peugeot went from N2 to R0, I'm not sure of the 'other sides' part number. As I say, as far as I could tell there was no other change such as internal workings to engines. At the time I could not work out if the filter 'design' was to simply filter a bit less to extend its life (and therefore oil pressure) or something else.
There is a lot I could say about DPF's and things but I'd rather not.
Andy.
91 205D-Turbo, gone but still missed
02 106D, TUD5B, gone but not really missed apart from the MPG