Need input on troubleshooting this oil reduction issue. There is no blue smoke or oil leakage. I am using 5W30 but the mechanic has asked to try 10W40. Car has 100k km on it. Oil reduction is like after 3000 km the oil shows at lower end of dipstick--almost end. Please advise as what tests can be done to pinpoint the issue. Feedback is appreciated. I posted the same question on yarisworld as well just to get more opinions.