Can you use straight 30 wt oil?

Yes, straight 30-weight oil can be used in certain engines, particularly those that require a single-grade oil for specific operating conditions. It's commonly used in older or specialized engines, such as small engines, lawn mowers, and some vintage cars. However, it's important to check the manufacturer's specifications, as many modern engines are designed to use multi-grade oils that provide better protection across a wider temperature range. Always ensure that the oil meets the necessary performance standards for your engine.