[Ray32825]

I hope you guys are changing the oil filter every time you do an oil change. Not doing so would be synonymous to wearing the same undergarments after taking a shower/bath.
An indication of a well-maintained engine is no varnish on the dipstick and inside the valve cover. Check your PCV valve to make sure that your engine is breathing properly this will help in maintaining a clean throttle body as well.
Also check your air filter and spark plug wires - no point in having expensive spark plugs if you wires and unable to deliver the high voltage necessary for a strong spark. I would change the spark plug wires every 50,000 kms preferably with the NGK blue wires.

[Nahid]

I am from Bangladesh and my car is Toyota Vitz. It's a JDM car and it's known as Yaris hatchback in European market. AFAIK this model is not available in India. It has a 1.3L engine which is made by Daihatsu (not VVTI engine). I am not a car expert so pardon my naiveness.

I previously knew that for Bangladeshi weather (which is similar to India) 10w-40 engine oil is applicable since the temperature in winter is about 10 degree and in summer it's about 40 degree. Then I googled before changing the engine oil for the first time and came to know that it's not about temperature it's about viscosity.

I changed the engine oil about three months back according to the suggestion of a renowned service center of Dhaka. They said that the recommended engine oil for this car is SAE 0w-20. I also found the same on the car's manual. So I used Revenol SAE 0w-20. It's full synthetic oil and the garage men said it will run about 5000 km. So far the engine oil is good after running 2000 km.

But some of my friends are saying that 0w-20 is not appropriate for our weather even though it's written on the manual. They say I should have been take 0w-30 or 40. Should I hear them or should I go by the book?