Originally Posted By: 440Magnum
Originally Posted By: weasley
So one wonders why diesel engines don't suffer intake valve deposit problems in the same way?
No mystery there at all. Diesel engines have no throttle blade in the intake path, the air velocity and volume flow over the stem of the intake valves is high all the time- even at idle. there's virtually no reversion flow out of the cylinder into the intake, no vacuum in the intake, and the intake is comparatively cool with fresh air constantly sweeping through. Even in a turbo application where the intake air can be very hot, there's no vacuum and little reversion.
A GDI engine has a throttle, so at idle there is very little airflow, a lot of reversion (back-flow) out of the cylinder and into the intake that can even include exhaust gasses from the previous combustion cycle, and there's a high vacuum condition in the intake that draws oil past the intake valve stems and into a hot, stagnant, condition that's ripe for cooking it to hard carbon deposits.
Great explanation. Even I can understand that.