QUOTE(mayalab @ Sep 11 2016, 02:56 PM)
FYI this chart is only recommended reference for start-up of the vehicle.
When the ambient temperature is 5 degree Celsius, we know 0W-20 provides a better start-up than 5W-40 of the same grade oil. When the ambience temperature is 40 degree Celsius, the start-up is not much difference between the two. I think we all know this principles well.
The car should have an operating temperature of around 90 degree Celsius. When a car is running, the ambient temperature is pretty negligible contribution towards engine temperature. The oil is designed to keep running at the this optimum operating temperature, be it ambient temperature is 10 degree or 40 degree Celsius. Your car works the same way as your body. Your body temperature don't go up to 40 degree Celsius just because ambient temperature is 40 degree Celsius. That's why your car's temperature sensor always read a constant 90 degree Celsius. You don't see your car's engine gives you a reading of 100 degree Celsius, just because of an extremely hot day, unless your water pump/temperature sensor is faulty. So the assumption of 'my car runs hotter on a hot day, and a more viscous oil needed' is basically flawed.
The key to select a proper engine oil spec is always refer back to the car manual. It is written as 0W-20, which means the engineers have done enough testing to tell you what is the best for the engine.
Of course there are many drivers out there prefer to stick to thicker oils, mainly due to perception issues. However, scientifically the manufacturers have been telling you what is good for your car.
The manual of Honda Malaysia not only suggest 0W20... It also suggest 0W20, 0W30 , 5W30 and 10W30..... There will alway trade off between different viscocity EO given the same Brand/ quality of of EO.... 20 will give better petrol mileage whereby 30 will give more protection against the moving part of the engine....
As the syaing says, there will be no one size that fits all.... The choice will be depend on the individual requirement and any other parameters such as driving style, ambiance, priority of the individual itself...
There no issues of perception, its more on experience as a person who already drove, maintain and owning different types of cars for nearly 30 years....
Unlike yesteryear, today manufacturer wont build a car that will last forever or else they will be run out of business....