2014 Thunderbird Commander Oil

Can't help I'm afraid but hopefully someone will pipe up soon enough, however from what I understand 10w50 is slightly thicker when up to temperature so if you're in hotter climates I might be tempted with that (no real knowledge though)

 

I would suspect that 40 viscosity is actually recommended, and I would think more like 30 is the makers' recommendation, all using higher viscosity will achieve is to slightly increase oil pressure and higher loads on the oil pump and its drive, It can be beneficial on a very high mileage engine with increased clearances and low oil pressure but on a good motor its really not needed, if you're using a synthetic oil then it will handle high temps anyway.

 

10/40 semi synthetic is what I've used in all of my three Thunderbirds to date.