The 2008 ford taurus came equipped with a 3.5l v6 engine across all models and there was no option available for any other motor in this vehicle. you're going to need to use 5w-20 synthetic oil. ford recommends using their own motorcraft brand. many owners prefer this too as this oil was made for these engines so you're going to receive increase performance when using it. the capacity will be 5.5 us quarts when the filter is included. you'll need to change out the oil every 7,500 to 10,000 miles for this engine. the oil drain plug is going to have a head size of 15mm and require about 25 ft-lbs of torque to remove it.
To protect the 2008 ford taurus engine's warranty, it is recommended to use motorcraft sae 5w-20 or an equivalent sae 5w-20 oil meeting ford specification wss-m2c930-a.