hey i heard that if your engine requires say for example SH type oil that you can use other letter types as long as the come after your current type. for instance you can use SL and SM since L and M come after H but not SF. Is this true?

 

That is true. The letters farther in the alphabet denote a later standard, which corresponds to a stricter level of oil performance. Oil with a higher letter meets all the previous standards and can be substituted for oil with a lower letter.