I own a 1998 Camry with 72,000 miles. This is one of the engines that has the potential sludge problem, but I have not seen any evidence of sludge in my engine. I have been reading here for about a month and have made the decision to switch to synthetic based on the advice I got here. My desire is to avoid the sludge problem. I have used dino up to this point with oil and filter changed at every 5,000 mile. I could have extended it to 7,500 miles per Toyota, but was not comfortable with that. I intend to clean the engine, probably with AutoRx, then switch to synthetic and do either 4,000 or 5,000 mile changes (not sure which yet). I know I can go further, but do not want to take a chance. Toyota recommends 5W-30 for my car, with their second choice being 10W-30. In looking and comparing, I noticed that most of the synthetic manufactures say the 5W-30 is recommended for "newer cars". The 10W-30 is recommended for "high mileage vehicles" (over 75,000 miles). The weather here gets in the 90's in the summer, and rarely below 10 in the winter. So which is best for me and my Camry?