I was reading on a Duramax forum that they use 1 gal. of 2 cycle oil. I never tried it because 2 cycle oil is kinda high. My uncle told me to add a quart of ATF to tank of diesel, he said it cleans injectors and lubricates fuel system. I have tried this and it quitens my psd a little. On the Duramax forum they talked about a quart of 30 weight oil. I have never tried it either.