*My understanding was more oil vapors (i.e. higher NOACK) would likely increase deposits ?
Originally Posted By: Gokhan
Originally Posted By: ChrisD46
A number of newer vehicles with GDI engines state to use 0W20 as preferred and in areas where it can not be found up to 5W30 is acceptable (i.e. Mazda Skyactiv 2.0L) until you can locate 0W20 oil . I believe typically the synthetic 0W20 will have a higher NOACK value which in a GDI engine you would want to use the lower Noack 5W20 synthetic oil if you had a choice ? ... *Are OEM's of GDI engines (Mazda again) trying to ensure that with a 0W20 you will have to use full synthetic OR a synthetic blend at a minimum versus stating a 5W20 is also acceptable out of concern you will use a conventional 5W20 instead of a lower NOACK oil in a GDI engine ?
Also , if I have a GDI engine (Mazda) , I don't live in a very cold environment - then why wouldn't I want to use a 5W20 synthetic in my GDI engine and enjoy a lower NOACK that would aid in keeping intake valves cleaner than 0W20 with the higher NOACK ? Other than cold start protection I can't see a reason to use a 0W20 synthetic versus a 5W20 synthetic oil ... Your thoughts and experiences ?
You have a lot of misconceptions.
NOACK has nothing to do with deposits. Reducing the NOACK is primarily for reducing the oil consumption. Why do you think if an oil evaporates faster, it would leave more deposits? In fact, it's the other way around. Base oils with lower NOACK/lower viscosity have lower aniline points, which means higher solvency and cleaning power.
Also, 0W-20 tends to have better base stocks than 5W-20, which also decreases deposit formation.
Therefore, 0W-20 cleans better than 5W-20 and leaves less deposits. However, the relative wear performance of 0W-20 vs. 5w-20 is more debatable.
It's also one reason why German Castrol and Mobil 1 European Formula are 0W-30 and 0W-40, respectively, instead of 5W-xx -- European engines require better cleaning.
See the section under solubility. Lower aniline point indicates higher solvency:
https://www.tri-iso.com/documents/exxonmobil_chemical_spectrasyn_plus_Brochure.pdf