Originally Posted By: Quattro Pete
Originally Posted By: tig1
Please explain "what rock have you been under? While you are at it(which you didn't do)explain how oil can cause deposits on valves?
This topic has been covered hundreds of times on here, tig1. A quick google search would provide some insight. Here is one of the first links that pops up....
http://www.aa1car.com/library/intake_valve_deposits_gdi_engines.htm
Quote:
What Causes Intake Valve Deposits
Intake valve deposits form as a result of oil slowly seeping past the intake valve guide seals and down the valve guides. A tiny amount of oil is necessary to lubricate the guides, but when oil reaches the hot surface of the valve, it can stick and burn forming heavy black carbon deposits that gradually build up over time. The higher the mileage on the engine and the greater the wear in the valve guides and seals, the faster the accumulation of black carbon deposits on the intake valves. Low viscosity motor oils (such as 5W-20 and 0W-20) may make the problem worse because they are thinner (to reduce friction) and flow more easily down the valve guides. Conventional motor oils also have a lower flash point than synthetic oils, which can also increase the formation of deposits over time.
Another contributing factor to the formation of intake valve deposits is unburned fuel vapors and oil vapors being siphoned back into the intake manifold through the Positive Crankcase Ventilation (PCV) system. This is done to control crankcase emissions and to remove moisture from the oil (which helps prolong oil life). The fuel vapors, carbon particles and oil droplets that the PCV system routes back into the intake manifold are reburned in the engine to reduce pollution. But these same vapors can also form carbon and varnish deposits on the intake valves.
The more blowby an engine has due to cylinder and piston ring wear, the greater the volume of crankcase vapors that are pulled back into the engine by the PCV system. High mileage engines typically have more blowby than low mileage engines, so the build up of intake valve deposits is usually faster.
Poor valve seals have been a leading cause of valve and piston deposits for decades, not just with DI engines. The Ford 4.6 had serious valve seal issues up to 96 when they were re-designed. My 69 Ford 6 cyl had valve seal issues as well, and caused serious piston and valve deposits. I replaced then twice myself. Chevy V8s also have a long history of valve seal problems, which I replaced on my 77 Nova 305.
In recent years I have been using 0-20 oils in my Fords, but when I bore scoped both Duratechs a couple of years ago not a single oil generated deposit was found on the pistons. Also I couldn't see any deposits around the valves that were open. The valve stems and guides are lubed by oil for sure, but quality seals and seal design will prevent oil from getting past the seals, in the same since oil won't get past front and real main seals until the seal becomes damaged and needs to be replaced. If enough oil is passing by the valve seals then some of those deposits will form on the piston also. Perhaps valve stem deposits are caused by the oil vapors. We do know oil vapors cause gunk to collect around the throttle plate and TP sensor which needs to be cleaned every 1-2 years. Or at least should be. Just a thought,
but what ever is causing serious valve deposits with DI it shows me this DI stuff is technology in reverse.
