2018 Acura RDX: What is the oil type and capacity?

While the 2018 Acura RDX comes in five different configurations, there's only one engine used -- the 3.5L V6. Therefore, variations are irrelevant to our discussion. You're going to need 4.5 quarts of SAE 0W-20 synthetic motor oil with a filter, or 4.2 quarts without a filter. Furthermore, You can use 5W-20 motor oil in a pinch, but it's not recommended for prolonged periods of use. In essence, an oil's weight is its viscosity at varying temperatures. The first number (0 or 5, in this case) is its viscosity at startup temp. The second (20) is its viscosity at full operating temperature. Lower numbers are better, so the SAE 0W-20 will keep Your engine running more efficiently, which will eventually lead to a longer engine life.