Quote:

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




You may want to do a little research before calling someone else wrong. And if you used to "spec" diesel oil why don't know how to spell "diesel". Actually, Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil

At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot. Maybe we just aren't looking at this the same way but I absolutely know that in the instance of a 20W-50 oil the base stock IS 20W and the polymer additives give it 50W properties.