bro there are two ways to maintain any machine either you maintain it in best way possible and perform good as new or in a way that it would just be ok.
if u wanna take the best route, here is it what i suggest you or any one else with a new car should do.
1 change oil after first 1000 km or in other words when running is complete
this would allow any metal particals that have be machined during the running in off the engine to be disposed off earlier, rather then be allowed to remain in engine. most of the time they are small enough to be missed by naked eye and at times even smaller enough to pass through filter. trust me i have seen small things pass through filter and then eventually become large enough after being deposited over and over again to have an impact. plus not to mention that toyota puts in cheapest oil in ur car to keep profit margins high. the things is you might never notice the small impacts these deposits make . but prevention is better than cure.
2 . secondly abt the oil, now most people here have a very rudimentary idea of what does oil grades mean and why a certain oil is better than other oils. the thing is oil does lubrication, cooling and cleaning of the engine. and in some engines like honda vtec it even acts as hydraulic oil for engaging vtec system, true its not relevant to corolla but just to tell that an oil does lots of jobs. a 5w50 oil is not a thicker oil then say 10w40. The first no like 5w means that how much the level of viscosity the oil will retain in colder temperature and the other number means how much will it retain when the engine is warm and the ambient temperature is hot. for e.g if say the optimum oil viscosity(thickness) required by the car is 8 then a 5w oil will maintain the value at or near 8 up till its -10 C outside and 50 means that oil will maintain the value 8 or near it when its 40+C temp outside . so bottom line is oil viscosity range defines the temp range in which the oil will holds its desired viscosity so if u look closely the manual even has a bar daigram showing temp ranges of various oil grades so that u can choose oil wrt to your environment. if u live in say muree , Islamabad where temp can go below 5 C than 20w50 isnt a good oil for u, yes it will work but its not the optimum oil. the cold temp viscosity matters cause the journal bearings or big end beaings in partcilar that rotate on crankshaft require to hydrodynamically lubricated meaning the rotation of bearings on crankshaft creats a film of oil on which the bearing rides. now during the cold start if oil viscosity is not as required then the the wear on bearings will be greater, now it doesnt mean it will break ur engine right away but it will reduce its life over period of time. remember every engine made, is made witha tolerance or safety margin. because toyota knows not everyone operating their machine would be well informed, educated or care enough. so they over design engine to take a beating. so like i said before two ways to maintain any engine. so keeping our envoirnment on view 5w30 or 5w40 are the best oils as they provide required temp range for our country. now there is a Toyota manual doing rounds on pakwheels which states 0w 20 oil for corolla . but the thing is that manual is from Toyota Canada for canada. another thing is that cleaning done by oil, now as we all know oil forms film between liner and piston too and then its wiped back evry time piston moves up and down what oil is additionally doing during this, is absorbing combination byproducts like carbon and etc. now these byproducts degarde oil chemistry because well they are basically chemicals. so oil companies add additives which neutralize and absorb these byproducts so that at first they dont create sludge and carbon deposits in the engine and dont chemically breakdown oil and its lubricating qualities. that's why better oils have longer change interval than cheaper oils .now all these grades like SN and CF that we hear basically define the standard of high quality additives add to oil to improve its cleaning and film formation capabilities. Now as these additives are expensive to blend in oil and for other reasons mostly synthetic oils grades of 5w30 and 40 especially in Pakistan have better additives and therefore are generally the optimum choice for our cars.
Now manu people here will say that they are using 20w50 for 200000kms and now issue well they might be right but you don't know their exact definition of great performance plus what envoirnment they have driven their cars. may be their oil change intervals have been less at 3000 km. the point is there are various factors that can influence opinions . best things to do is go with the science.
so summary is as follows change first oil at 1000 km always use genuine oil filter and then at 5000 km use 5w30 or 5w40 oil like shell ultra or havoline gold or liqui Moly of or above SN and CF grade.
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