It is a jaguar engine.
Ford used the engine design from Jaguar, and built the motors in there plant, but it still is a jaguar motor design. It still is a AJ-V8.
The 2009 Jaguar Cars with the AJ-V8 still call for 5w30.
No, actually the engine is not a Jaguar engine; it is a Ford engine which uses Jaguar architecture. Did you not read anything I wrote?
This AJ30/AJ35 is NOT used in ANY Jaguar, the block, pistons, rods and crank are ALL proprietary to this specific engine.
There is a distinct difference between taking an engine built by Jaguar and dropping it into a Ford vehicle (which is not what happened) and Ford engineers taking the architecture and layout of a Jag engine, then building it to their specs (READ: DESIGN)... which is exactly what happened.
Maybe when FORD DESIGNED the engine they opted to run bearings that contained a different Aluminum than most other engines in the series and this required a thinner oil because they expand more at operating temp.
The point here is Ford used the architecture; they did not just take a specific engine from Jaguar and put it in the LS and Thunderbird. Even the VVT used on the AJ35 is different from the VVT used by Jag.
Make an attempt to remove your head from your 5th point of contact; YOU LISTED FOUR SEPERATE OIL WEIGHTS that other engines of the series call for... again FOUR SEPERATE OIL WEIGHTS... Obviously this architecture doesn't "require" a certain oil weight if the engines found in Jaguars call for FOUR SEPERATE OIL WEIGHTS. (and for the record, correct oil weight for an engine is determined by bearing material, operating temp, expected use of the engine, clearances and the molecular make up of the materials used to make the engine and it's various parts; all of these things were determined by FORD... not Jaguar)
Ford set the specs for this particular engine... are you going to bitch about the fact that it's 3.9L instead of 4.0 or 4.2? They set the specs, they built the engine... they can put whatever the hell they want in it.
Anyway what are you trying to prove with all of this? There have been several members on here with 130,000-150,000 miles on their cars with original engines... obviously the oil is doing the job it's intended to do.
If you're an engineer at Ford and you have some sort of hard data on why Ford shouldn't be using 5w20... then please enlighten us. Otherwise, you're just another noob rattling off BS with no hard facts or information to back it up... nothing but speculation.