Originally Posted By: Y_K
Could you please explain the physics/chemistry of the premise? I am not arguing, just trying to learn more, as we all have to face the DI revolution sooner or later, it seems.
Thank you
The premise is that the intake occlusion/contamination issues are mostly caused by recirculated volatilized products of motor oil depositing on intake components as they mix with fresh intake air and are drawn into the cylinders as part of the intake air charge.
Motor oil volatility is at its peak when the oil is brand new. And declines over time as the oil is in service and is subject to repeated distillation inside the engine under the vacuum imposed on the crankcase by the PCV system.
So to fix the problem, simply minimize the volatility of the oil. By both selecting the least volatile oil as possible. And using that oil in its least volatile condition -- when its been in-service for a while, minimizing the exposure to 'brand-new' oil which is susceptible to higher distillation loss.
In Europe, and even in the manufacturers' labs in the USA, the problems could not be replicated, as manufacturer-recommended maintenance practices were adhered to in the test environment (over-maintenance isn't generally a usual test case!) and the actual European end-user environment. A few years back, I personally did a meta-analysis, on BiTOG, of a lengthy car-proprietary non-BiTOG forum thread where people were complaining of issues -- there was a very strong correlation between improper maintenance practice (too frequent oil changes) and intake contamination.
Also, manufacturers have tightened the volatility spec severely over the past few years in response to the DI intake contamination troubles. Ostensibly because controlling volatility is a significant component to the overall 'solution' to this problem.
Some people have had decent luck with "catch cans" and other inserts to the PCV/breather system. If there's no adverse affect on instrumentation or the normal characteristics, this can be a valid solution albeit requiring additional maintenance. However, it really doesn't address the root cause of too much, and too poor of quality motor oil causing the problem in the first place.
