WHAT ????
YOU HAVE THAT BACKWARDS
30 is 30
10w 30 10w 40
5w30
it is a 30 w until the temp starts falling
below the 32^
then it stats to act like thinner
wieght for easier starts in winter
i used to spec out oil for trucking companies
desil oil have certain properties to help in sludge/ breakdown additives and soot control