Originally Posted by
TheGrandPoohBah
My GMC Sierra takes 8 quarts of oil for a change, and not just synthetic - it has to be Synthetic "Dexos" 0W20, I use the Mobil 1 version. The "Dexos" designated oil has special chemicals/cleaners to address concerns unique to direct injected engines, among those are soot and cleaning of the intake valve areas, since no fuel goes in that way via the valves, it is direct injected into the combustion chamber. Excess PCV fumes can lead to problems, so aftermarket companies are promoting "Catch Cans" to capture oil fumes instead of routing it to the intake valves/combustion chamber. If you overfill the oil, it makes the condition much worse, so one thing we can do is run the oil level about a pint low - halfway in the "Etching" on the dip stick, which is still regarded as "The Safe Zone". On down the road, with a high mileage engine that shows a loss of compression, piston ring wear will increase "Huffing", which will send more oil to the intake valves if you don't have a "Catch Can" to capture it. In the old days, these fumes would vent out the oil cap, but the EPA wants them burned.
Years ago in an old Chevelle I had, I installed Oil Vent Caps in both valve covers, attached huffing hoses that went down to remove those fumes under the car to keep my chrome valve covers clean. Big loping cams loved to huff and puff under load, or at that idle that we all know and love!