Why does the owner's manual for a 2000 Accord V6 call for 5w30 oil while a 2001 Accord with the same engine calls for 5w20?

Answer 1

Thinner oil gives less friction, hence improves fuel economy.

Blame for this one goes to the feds...they said "make your cars get better fuel economy right now," and everyone said "okay, run thinner oil in them and you'll GET better fuel economy."

AnswerI can't specifically explain it for an Accord. All I can offer is that there seems to be a trend by manufacturers to specify lower viscosity oils. E.g. My 1988 VW Golf recommended using 20W50 in the summer, if not straight 40 weight. My 1988 VW Golf recommended 10w30 or 10w40 in the winter. That makes sense to me: "thicker" oil when the outside temperature is hot. The normal service recommended oil change interval was 7500 miles. Engine lasted ~230,000 miles with only slight oil burning at the end.

My 1997 Ford Escort recommends 5w30, year round. When I first saw this, I found it hard to believe: Ford is saying use the same weight oil during the summer in Arizona where the ambient temperature might be 110 F, and the exact same oil in the winter in Maine when it might be -20 F? BTW the normal service recommended oil change interval is 5000 miles. At 150,000 miles, the engine is burning about 1/2 qt. of oil every 4000 miles.

Now my 2003 Mazda MPV, with a Ford engine in it, recommends 5w20. I do have concerns about engine durability/lifetime with the lower viscosity oils.

If any oil/engine guru can explain the reasons and justifications for these changes, PLEASE do!

I read somewhere said modern engine component are tighter than before, thinner oil will make it flow faster and easier. But I do have the same concern since I live in So California which summer high will be up to 105+ and 30F in the winter. And Honda recommend 5w-20 at all time. But better follow the manufacture recommended.