I dont think i'll add anything new but here is what i know:
I use Mobil 1 full synthetic oil, this oil when for ordinary use (no offroading or racing) is fine for 10,000 km ... in my case i use my jeep for offroading mainly (% of the time is offroad) so i change oil every 5000km ... so it all depends on your use and driving style.
i'd say go for Mobil 1 and change the oil every 5000 km if the car is used for offraoding only, but if its an everyday car and you offroad during the weekends then change the oil every 7000 km (approx) as megamoe said ... and at the end it depends on your driving style ...
one more peice of info, you have to change the oil after 3 months regardless ... i mean if the car is just sitting you still have to change the oil after 3 months from the oil change even if it didnt move. my car during the summer doesnt usually move alot so it covers like 2000km in 3 months during the summer.. so i go along and change the oil. i hope you got the idea ...
Good Luck Man
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