Why is 5w30 better than a 10w40 in cars above 100000 I have got a 99 accord V6 with 165000 been running 10w40 it's whole life still strong?

Answer 1

Modern engines are designed with very close tolerances. These close tolerances require a light weight oil at startup to ensure the components are properly lubricated. They also require a 30 weight oil after the engine reaches proper operating temperature to make sure the engine is lubricated as it should be. 2003 and up Honda engines recommend you use 5w20 oil, due to the extremely tight fit of all components. Luckily you do not own a 2003 or newer Honda or you would have done damage. You are assuming that the engine will wear enough to require the use of a heavier weight oil after it reaches 100,000 miles. This is not necessarily so, on modern engines. They are built so good as to not wear signiicantly if you follow the manufactures recommendations and perform maintence according to their schedule. Why in the world would you ignore the recommendations of the engineers who designed and built your Honda engine and use 10w40 oil. You think heavier is better? That is a weight that has not been used in over a decade. Do you think you know more than the people who designed and built the engine? Now if the engine was actually burning oil then you might want to use a heavier oil to help stop some oil burning. All I can say is that your Honda has been an excellent car to still be running strong even though it's owner ignored the recommendations of the manufacture and has been using the wrong weight oil for 9 years. That is one well made engine. Answer 2: 5w30 and 5w20 weight oils are mainly for CAFE requirements. Also, clearance does not mean the same as tolerance. Engines have tight clearances, a tolerance is an accepted or maximum variation in a given measurement. Thicker oils typically do not harm engines, unless you go extremely thick or use thick oil in a cold climate. Many European cars spec an Xw40 oil, not just cars built in Europe but cars that are imported into Europe.