Land Rover list both 5w30 and 10w40 as suitable. I personally prefer to use a thicker 5w40 fully synthetic oil in the TD4.Would the crankcase breather blockage be causing white smoke from exhaust ? Also the service kit I've order comes with 5w 30 semi sythenic oil but when I went to Halfords for the litre they gave me 10 w 40 semi sythenic does it matter which one I use ? Thanks