The letter 'W' means both varieties are suitable for cold temperatures. ... So, 0W20 means the oil's viscosity is 0 in cold temperatures and 20 at the operating temperature. The 5W20 oil is the same except for a viscosity of 5 in cold temperatures. Both oils are designed to use in cold-weather regions.
My owners manual specifies 5W-20 or 0W-20 oil. Do I really need to use 5W-20 or 0W-20 oil and why did my 2000 model year vehicle require a 5W-30 oil, while the exact same engine in my 2001, 2002 and newer engines "requires" a 5W-20 or 0W-20 oil?
Answer: NO! You do not need to use a 5W-20 or 0W-20 oil. Do not let your dealer scare you by telling you that you have to use 5W-20 oil for your warranty. That is a tactic that some dealerships use to scare customers. Once you know the facts and the Federal Magnusson Moss Act law, you will be much better informed to protect your rights and use the type of fluids you want to use.
The main reason 5W-20 or 0W-20 oil was specified for your engine is to increase the CAFE (Corporate Average Fuel Economy) reported to the Federal Government. CAFE is the combined average fuel economy of all of a vehicle manufacturers product line. Minimum CAFE levels are specified by the Federal Government. In order for a vehicle manufacturer to continue selling profitable large trucks and SUV's, which typically have poor fuel mileage ratings, as compared to smaller cars, and still meet mandated CAFE requirements, they must also sell enough of the smaller cars which have much better fuel economy ratings to offset the poor fuel economy ratings of the larger vehicles. For model year 2001, the change to a 5W-20 oil will allow Honda and Ford's overall CAFE to increase by a very small amount, typically in the tenths of a mile per gallon range. 5W-20 oil is a lighter viscosity than a 5W-30 oil and therefore has less internal engine frictional losses, or less drag on the crankshaft, pistons and valvetrain, which in turn promotes increased fuel economy. This increased fuel economy is virtually undetectable to the average motorist without the use of specialized engine monitoring and testing equipment under strictly controlled test track driving when compared to a 5W-30, 10W-30 or a 0W-30 viscosity motor oil.
