it is the additives they put in the oil
Viscosity. 5W-30 is a "thinner" oil than 10W-40 is.
The 50W is not a multiviscosity.
One quart of Mobil Special 10W-40 motor oil weighs 1.8 pounds. Not all motor oils have the same density, and one gallon of motor oil will weigh between 6 and 8 pounds.
any 10W-30 Motor Oil
It is the difference of two squares which is: (6-10w)(6+10w)
The recommended temperature range are as follows 10w30: -13 F to 100 F (-25Celsius to 38Celsius) 10w40: -13 F to no limit (-25Celsius to no limit) In other words the difference between the two oils You are hesitating is, the 10w40 has same performance at low temperatures, but works well also above 38C/100F
yes
10w-40
10w 30
Yes
it needs 10w-40
Pennzoil 10W-40