What actually changes
The two numbers in a grade describe different conditions. The first number with the W (winter) rating describes how the oil flows when cold, and the second number describes its thickness at full operating temperature. With 0W-20 and 5W-20, the second number is identical, so once the engine is warm both oils provide the same film thickness and the same protection. Nothing meaningful changes for high-temperature operation, towing, or hot-weather driving.
The only real difference is cold-start behavior. A 0W oil is engineered to stay thinner at very low temperatures, so it reaches moving parts slightly faster on a cold morning. That is generally a small advantage, not a drawback, because cold starts are one of the higher-wear moments in normal driving. Going from 5W-20 to 0W-20 moves you toward easier cold flow, which is usually the lower-risk direction for a viscosity change when the hot grade and specifications still match.
Before you switch
Even though the hot grade matches, treat the manual as the deciding factor. Many modern engines list both 0W-20 and 5W-20, and where both appear the swap is straightforward. If only 5W-20 is listed, check whether 0W-20 is named as an approved cold-weather alternative. Manufacturers sometimes tie warranty coverage and emissions compliance to specific approved grades, so confirming the listing protects you on both counts.
Also confirm any required oil specification or approval code printed in the manual, not just the viscosity number. The grade tells you the thickness, while the specification tells you the performance standard the oil must meet. Matching both the listed grade and the listed specification keeps you fully within the maker’s guidance.