The 2005 ford ranger's3.0l srx cylinder engine requires the use of 4.5 quarts of sae 5w-20 full synthetic motor oil. this is the same oil type as the smaller 2.3l four cylinder, but notably different from the larger 4.0l engine's sae 5w-30. however, in a bind, it's still possible to use sae 5w-30 in your 3.0l, but it's use is not recommended, especially over the longer term. this is due largely to the latter oil's thicker consistency, as evidenced by its higher weight. the thicker the oil, the more friction it will introduce into your engine's operation. more friction means more premature wear and tear, which can eventually lead to early engine failure. therefore, you'll want to use the manufacturer's recommended oil -- in this case, sae 5w-20 full synthetic -- whenever possible.
The oil capacity of a 2005 ford ranger 3.0 is 4.0 quarts.