Here are a string of attachments that list fluid specs for Land Rover vehicles.

NOTE : A coolant specification change has been made for Range Rover vehicles. The 2005 specification "G48" fluid is to be used for every FLUID CHANGE situation. The original Texaco AFC coolant fluid may be used and topped up until a coolant change is required. Mixing Texaco AFC and BASF G48 for top-up purposes is permitted CAUTION : Mixing of the BASF G48 with Texaco XLC coolant used in LR3, Freelander, Discovery Series II and late Range Rover 4.0/4.6 can result in premature erosion of the cylinder heads or other cooling system deterioration. Unapproved blending of coolants is to be avoided. Warranty coverage could be affected by the use of unapproved coolants or the incorrect blending of fluids.
Failure to use specified fluids could lead to component failure. If component failures are found to be caused by use of improper fluids, warranty charge-backs could be impose

 

One last one...

 

 

So how come the RAVE lists 20W50 as an acceptable viscosity in warm weather use?

 

I don't know. Write to Land Rover and ask them.