Can you use 15w40 in a 4L80E transmission?

Using 15W-40 oil in a 4L80E transmission is not recommended. The 4L80E typically requires a specific type of automatic Transmission Fluid (ATF), such as Dexron III or a compatible fluid, to ensure proper lubrication and function. Using motor oil like 15W-40 can lead to poor shifting performance and potential damage to the transmission components. Always refer to the manufacturer's specifications for the correct fluid to use.