I browsed several topics and tried a search but was not able to locate an answer to my questions. Please help out a new person trying to learn about oil. Based upon my needs I have decided upon using Chevron Supreme dino for both of my Hondas. A 2002 CRV-EX which recommends 5W-20 and a 2000 Accord SE which recommends 5W-30. I currently have 5W-30 in the CRV and 10W-30 in the Accord. Will I do any harm to either engine running 5W-30 or 10W-30 over the long term. My weather is in the 90's several months a year and usually have 2-3 months of temperatures in the teens during the winter. Both cars are garage kept. The Accord has a twice daily commute of under 5 miles each way. I am not concerned about gas mileage and not too worried about warranty (the Accord will be out of warranty in 4K miles anyway). I currently change the oil as recommended by severe maintenance schedule (every 3,750 miles for the Accord and every 5,000 miles for the CRV). Replacing with Champion SuperTech filter at every oil change. It is time to change the oil in the CRV and I plan to send off the Chevron off for lab analysis and will post the results here since I saw several people interested in seeing how this $1 oil holds up in the real world. What are the ramifications and differences of using 5W-30 instead of the 5W-20 recommended by Honda? What would happen if I used the 10W-30? I just want to use whichever is most likely to give me longterm engine protection. I appreciate your feedback since I am not nearly as knowledgable as most of the members on this site.