Originally Posted by Olas
DI or PFI is not the issue - polluting your inlet tract is the issue. Don't dirty your inlet and you won't dirty your valves. Simples.
This.
The main sources of intake tract carbon fouling are:
1. EGR. Just swipe your finger along the exhaust tip of your GDI vehicle to see how much unburned carbon is put out by the rich mixtures created by the DI system for cylinder cooling and anti-detonation. This is being sucked back through your intake and gets deposited on your valves and intake tract just as it does on the exhaust tips. In fact, it's worse, due to oil mist from the PCV system getting the valves all wet and sticky.
2. PCV. It's sending oil vapor and mist back through. And, obviously, higher-SAPS oils leave more deposits. This is why lower-SAPS oil is a good idea for these engines. And, the lowest Noack volatility rating oil, because, the more stable the oil is, the less vapor it will send back through the intake, and the fewer deposits. Also, a more stable oil will resist fuel dilution better.
The inherent fuel dilution that comes along with GDI (and especially TGDI) engines just makes things worse because when you add a solvent to the oil (gasoline), you effectively raise volatility, and lower the temperature at which the oil starts to off-gas these volatile vapors that condense in the intake tract.
Someone suggested using an MB 229.5-certified oil, which will have lower SAPS as well as Noack volatility rating of
Which...as someone else mentioned...it's weird that the VME 0W-20 (which I just bought a BUNCH of from the AZ clearance) is pretty high Noack at 12% or so.