Thought I would share my experience switching from the Castrol 0W20 to Liqui-Moly 5W30. The engine felt more smooth, sounded much more quiet and healthy especially with the hood up - It took me by surprise. Oil consumption has dropped from 1L every 9000KM to 1L every 15,000+KM. Note that in the rest of the world the following oils are approved:
There is nothing wrong with using the approved, FAR more proven 5/10W
oils for this engine, especially considering that 0w20 has been around for merely 5 years and has absolutely zero track record as being reliable in high mileage situations. This engine is clearly built around very high performance as the max 10W50
oil weight approval may suggest. According to my mistake, the oil pan can hold at least a quart of oil past it's recommended fill level with zero issues for an extended period of time. This means our engine has a very aggressive and high-performance oil-pan that ensures the engine is not starved of oil during full throttle high speed corners. All of this makes it clear that we are dealing with a high-performance engine designed around upwards of 10W50.
Let me just make one point before I hear "modern tolerances" again. The Mazda NA 2.5L, code-named PY-VPS is a modified evolution of the previous generation L5-VE 2.5L engine. This Skyactiv motor is NOT
a clean-sheet design. Both engines have identical Bore X Stroke dimensions and overall displacement. This means that the internal-tolerances are NOT modern. Do you seriously believe that 10W50 and 0W20 have the same amount of protection in hot-weather? Please refer to this picture here, an oil temperature chart from Mazda before the CAFE shit:
As you can see, even 5W20 is only good for very cold weather, let alone a 0W. Thick oil and thin oil Obviously
does not protect the same in hot weather. Now go back to what CAFE
intends to do. It stands for Corporate Average Fuel Economy, a program made by the government to lower emissions and increasing fuel economy by using oil with less friction. Each car gains a roughly 0.2 MPG increase in fuel economy, which when added up results in big tax credits/savings for manufacturers who choose to follow CAFE's requirements. Do you want a 0.2MPG increase in fuel economy or increased long-term engine protection? The choice is yours.
5w30, 5w40 oil, with the right additives included, helps to protect your engine from fuel dilution, which breaks down your engines oil supply because of the way direct injection works and all the sulfur in our fuel. This is a very important reason to always change your oil often, especially if you do lots of short distance city driving.
Another reason is carbon build-up on the intake valves which is a known issue with DI motors. It does not happen much with these motors, but there are recorded instances. According to Chris_Top_Her, a moderator over at Mazdas247 his oil catch can caught significantly less blow-by when using 5w30 VS. 0w20. This means that the thicker oil reduces the production of carbon build-up in your engines, particularly on the intake valves:
Your engine is designed to run at the same temperature year-round, regardless of how hot it is outside. However, if you like to drive aggressively, especially in hot weather where your engine-bay is more prone to heat soak, oil temperatures will inevitably rise. Thicker oil such as 5W40 helps maintain a thicker layer between the moving metal parts in your engine, thus reducing friction and increasing engine longevity. Bottom line, just use an oil weight appropriate for the ambient conditions you drive in and the way you drive. BMW M engines all use 10W60 oil which is not far off from the 2.5L's maximum oil weight of 10W50, meaning you got lots of room to choose an oil weight best suited to your driving style and conditions. All engines will inherently burn oil quicker with 0W20 since it is so thin, but using a thicker weight will likely stop oil consumption all together or at least noticeably decrease it.
Yes you can use 0W20. But unless you have perfect metal-wear ratings or plan to sell the car early there is a whole plethora of reasons why you shouldn't.