The one and only reason 0W is spec'd is for fuel economy. For me I don't like large spreads on the low and high viscosity numbers. Prefer to keep as tight as possible. If I was somewhere warm I would probably be rocking a 10W-30
FYI, that was on their TDV6 in the Discovery 3, which is a different engine design than the diesel available in the Discovery 4. Over on the Disco3.uk.co forums there is disagreement about this oil recommendation. The LR mechanics there stand by the 5w30 recommendation.LR Time recently had a YT video about changing the oil viscosity for the diesel LR4 engine. Part of what caught my attention was the research he had done on actual viscosity, and what was driving the pursuit of lower viscosities: emissions and mileage at the expense of engine wear.
He talked about the oil company web sites leading him wrong on what spec oil to use; not the 5W-30 part, but other relevant specs. The net result of the video was that he determined that a 5W-40 C3 oil, not the original spec of 5W-30 B1/B3. He’d looked into the HTHS specs across oils and tried to match up to what the OEM spec original oil was supposed to be. Then he added an increment to the upper viscosity number to try to get the oil pressure back to where it was supposed to be on his higher mileage engine.
It did get me wondering about the 0W-20 A1 spec oil I’m using on the SCV6, particularly when I’m going to be off-roading in Moab this summer. That oil just seems water-thin to me. But…if that’s what the manufacturer calls for, I guess best leave well enough alone.
I've always put in 8 qts. It's perfect level on the digital gauge. IIRC, get an 89mm oil filter wrench for the canister cap. It fits with less play than the normal 90.