What oil grade do most small engine manufacturers recommend for temperatures below 40 degrees?

Most small engine manufacturers recommend using SAE 5W-30 for temperatures below 40 degrees because this oil provides optimal flow and protection in lower temperatures. The "5W" indicates that the oil has a low viscosity at cold temperatures, allowing it to pump quickly and lubricate engine components efficiently even when the engine is first started. This is essential for avoiding wear during startup when the engine oil may not yet be fully circulated.

Using a higher viscosity oil, such as SAE 10W-30 or SAE 10W-40, could lead to sluggish oil flow in cold weather. This delay could increase the risk of engine wear and damage as parts may not receive adequate lubrication quickly enough. SAE 30, which is a straight grade oil, does not have the same low-temperature properties and would not be suitable for use in temperatures below 40 degrees, as it would be too thick to provide effective lubrication during cold starts. Therefore, SAE 5W-30 is the optimal choice for maintaining engine performance and longevity in such conditions.