Originally Posted By: Gokhan
Originally Posted By: ChrisD46
I believe for a GDI engine you would want as low a NOACK oil as possible to keep intake valve deposits at bay (along with top tier gas , shorter OCI's , etc.) with a GDI engine.
Nope, on the contrary, the lower the NOACK and/or higher the base-oil viscosity, the more the intake-valve deposits will be. Alternatively, the higher the NOACK and/or lower the base-oil viscosity, the less the intake-valve deposits will be.
This is because one mechanism of cleaning of the intake-valve deposits is evaporation. If NOACK volatility is low or the base-oil is thick, the oil will spend more time on the valves as it evaporates more slowly, therefore leaving more deposits behind.
Intake-valve and combustion-chamber depo...ts their growth
So, if you want the least intake-valve deposits in a GDI engine, you need to pick up a 0W-20 with higher NOACK. A 10W-30, which has both a thick base oil and low NOACK would be the worst choice as far as the intake-valve deposits are concerned.
From the article: "The most important lubricating-oil component for deposit formation is the base oil. Increasing the high molecular weight (high viscosity) and low volatility content of the oil increases deposit formation."
I would encourage anyone interested to read the paper before latching onto that single by line as a factual representation of the paper...it is Point 8 in the conclusions regarding intake valve deposits, and COmbustion chamber deposits out of 12.
The textual context of the IVD (Intake Valve Deposits, using acronyms conveys an understanding of hidden knowledge) is
Quote:
Taking into consideration that in the case of GDI (Gasoline Direct Injection) engines no fuel is injected into the intake manifold, so no fuel spray is directed on the intake valves
tulip, lubricating oil is seen to be a significant factor in the amount of IVD formed in the GDI engine. In GDI engines, lubricating oil has direct paths to the intake valves through
the valve guides and PCV (Positive Crankcase Ventilation) system, while fuel must be considered to interact with the intake valves in only a secondary fashion, such as through blowback upon intake valve opening. At the same time in the case of GDI engines lubricating oil flowing to the intake valves through the valve guides without washing by the fuel, in consequence quite often formed IVD in GDI engines which
is higher than in the PFI [4].