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Intake Valve Deposits in Gasoline Direct Injection Engines

Posted by on 3/15/2016 to News
Gasoline Direct Injection (GDI) is used on a variety of late model engines: Audi, BMW, GM, Ford, Hyundai, Lexus, Mazda, MINI, Nissan, Porsche, VW and others. A GDI sprays fuel directly into the combustion chamber under high pressure, rather than spraying fuel under low pressure into the intake ports in the cylinder head. GDI increases fuel economy and power 15 to 25 percent, but there is a downside that is now becoming apparent as these engines with accumulate miles. The problem is carbon deposits are building up on the inlet side (top) of the intake valves. The deposits can create turbulence and can restrict airflow into the cylinders causing performance and drivability problems (hesitation, stumbling, misfiring, and even hard starting). The thicker the carbon deposit buildup on the valves, the worse the drivability problems.
GDI sprays fuel directly into the combustion chamber so the fuel completely bypasses the intake valves. Consequently, detergents and cleaners that are added to gasoline to prevent intake valve deposits from forming in port fuel injection engines never have a chance to do their job in a GDI engine. The inlet side of the intake valves are never in direct contact with the fuel so the detergents cannot wash away the deposits. Because of this, fuel detergent additives that are either in gasoline from the refinery or are added to the fuel tank have almost no effect on preventing or removing intake valve deposits in GDI engines. The additives work in regular fuel injected engines, but not GDI engines.
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 re-burned in the engine to reduce pollution. But these same vapors can also form carbon and varnish deposits on the intake valves.
The more blow by 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 blow by than low mileage engines, so the buildup of intake valve deposits is usually faster. The Rx Oil Catch Can by McNally is an oil separating evacuation and separation device that eliminates valve coking issues, increases fuel economy by eliminating oil associated detonation, reduces tail pipe emissions, and prolongs engine life by removing these damaging combustion by-products from the crankcase and separating and trapping them from ingestion via the intake air charge.
The Rx Oil Catch Can by McNally removes from the PCV, compounds present in the vapors consisting of mainly water which is released during the combustion process when the extreme pressure and heat occurs. It also removes un-burnt fuel and sulfuric acid which forms when the water and other compounds mix with hydrocarbons and other compounds when they enter the crankcase. Furthermore, it removes oil vapor, abrasive soot, and carbon particles which bake on to the intake valves resulting in the severe valve coking.

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