Hi l have a 20 year old toyota camry, it recently had an oil leak which was repaired. l always used 5w 30w synthetic engine oil that the manual recommended for this car but but the mechanic put in 15w 40w mineral engine oil because he said a thicker oil will help it burn less oil because its an old car thats burning more oil then normal. l am worried that this thicker oil might not be good for the engine and do harm . l read thicker oil on start up doesnt flow as well to the parts and could harm them, but the mechanic said theres nothing to worry about. l am not sure if l should keep the current 15w 40w oil or should l ask to change it to a thinner oil. Also as its a mineral oil is that not good for the car, would synthetic oil be better.ALso l am in Australia, l dont know if we use different oils here