Neither oil is better or worse They are different from each other, certainly, and will react differently as well, but it would be a complete injustice to call one better than the other As we have just seen, both 10W30 and 10W40 have winter SAE oil grades of 10WThe newest push mower I purchased last summer, with a Briggs 675, has an engine manual included that says below 40 degrees 30W may cause hard starting, but that weight may be used up to and over 104 degrees, and 10W30 can be used in temperatures as low as zero, but use in temperatures about 80 degrees may cause increased oil consumption, with a ceiling illustrated of a naximum of about 98I did an oil change to 10W30 that night! Castrol Gtx 160 Fl Oz 10w 40 Motor Oil 159e The Home Depot 10w 30 vs 10w 40 oil