I changed oil last night but I had to use oil that was left over from
other oil changes. It was all new oil but some was 10W-30, some was
20W-50, and the other was something else in viscosity. All was the same
oil mfg...quaker state. Is there any problem with mixing viscosities as
long as the oil is the same mfg?

-matthew, a chemist at that!