Here’s part of our conversation about valve gunk, its effects on direct-injected engines, and whether there’s cause for concern. Apparently, proper maintenance and following manufacturer recommendations are key to long-term performance.
JP: What causes a buildup of ‘gunk’ on an engine’s intake valves? Is it only fuel, or oily engine ‘blow-by’ that accumulates over time from the PCV system?
GB: These deposits are formed from a combination of several different substances : Positive Crankcase Ventilation (PCV) blow-by, Exhaust Gas Recirculation (EGR) residue on those engines with external EGR systems, engine oil that may leak past the valve seals, and fuel residue on port-injected engines.
JP: Do all engines suffer from valve gunk over time?
GB: All engines will accumulate some buildup, but the amount is dependent upon a wide variety of factors including the geometry of the engine, the type of engine oil used, and operating conditions including engine load and drive cycles.
JP: Is oily blow-by more prevalent on performance engines or turbocharged engines?
GB: Not necessarily. As stated above, there are many different factors that can influence deposit buildup.
JP: As deposits accumulate on the valves, what happens to drivability and performance?
GB: On direct-injected engines, the typical symptoms are reduced high-output performance due to a disturbance or reduction in the airflow entering the cylinder past the intake valves. On standard port-injected engines, cold drivability and emissions performance can also be affected as fuel is absorbed by the deposits during cold operation.
JP: What happens when a DI engine gets valve gunk deposits? Is there a cleaning procedure?
GB: Typically on a direct-injected engine, the only way to clean the intake valves is to have the deposits removed mechanically. However in most engines, the amount of buildup is small and it will take a long time for the engine performance to be noticeably impacted.
JP: Do conventional ‘port’ fuel injectors typically ‘wash’ valve gunk into the cylinders where it’s burned off?
GB: No, unless the gasoline has the proper type and amount of deposit control additives. GM recommends the use of TOP TIER approved gasoline to ensure that the fuel contains the right type and amount of deposit control additive in all grades to prevent and reduce the buildup of intake valve deposits. At the present time in Canada, Chevron, Shell, Petro-Canada, Sunoco and Esso gasolines are all TOP TIER approved.
JP: So: what can owners of DI powered cars do to prevent the buildup of valve gunk?
GB: Using the correct grades of TOP TIER approved gasoline and Dexos-approved engine oil as recommended in the vehicle owner's manual will go a long way to ensure that intake valves are as clean and free from deposits as they can be, for as long as possible.
JP: Are valve-gunk related issues, if present, covered by warranty?
GB: The warranty covers repairs to correct any vehicle defect related to materials or workmanship occurring during the warranty period. Damage caused by failure to follow the recommended maintenance schedule intervals and/or failure to use or maintain proper fluids, or maintain fluids between recommended maintenance intervals, fuel, lubricants, or refrigerants recommended in the owner manual, is not covered.
JP: What causes a buildup of ‘gunk’ on an engine’s intake valves? Is it only fuel, or oily engine ‘blow-by’ that accumulates over time from the PCV system?
GB: These deposits are formed from a combination of several different substances : Positive Crankcase Ventilation (PCV) blow-by, Exhaust Gas Recirculation (EGR) residue on those engines with external EGR systems, engine oil that may leak past the valve seals, and fuel residue on port-injected engines.
JP: Do all engines suffer from valve gunk over time?
GB: All engines will accumulate some buildup, but the amount is dependent upon a wide variety of factors including the geometry of the engine, the type of engine oil used, and operating conditions including engine load and drive cycles.
JP: Is oily blow-by more prevalent on performance engines or turbocharged engines?
GB: Not necessarily. As stated above, there are many different factors that can influence deposit buildup.
JP: As deposits accumulate on the valves, what happens to drivability and performance?
GB: On direct-injected engines, the typical symptoms are reduced high-output performance due to a disturbance or reduction in the airflow entering the cylinder past the intake valves. On standard port-injected engines, cold drivability and emissions performance can also be affected as fuel is absorbed by the deposits during cold operation.
JP: What happens when a DI engine gets valve gunk deposits? Is there a cleaning procedure?
GB: Typically on a direct-injected engine, the only way to clean the intake valves is to have the deposits removed mechanically. However in most engines, the amount of buildup is small and it will take a long time for the engine performance to be noticeably impacted.
JP: Do conventional ‘port’ fuel injectors typically ‘wash’ valve gunk into the cylinders where it’s burned off?
GB: No, unless the gasoline has the proper type and amount of deposit control additives. GM recommends the use of TOP TIER approved gasoline to ensure that the fuel contains the right type and amount of deposit control additive in all grades to prevent and reduce the buildup of intake valve deposits. At the present time in Canada, Chevron, Shell, Petro-Canada, Sunoco and Esso gasolines are all TOP TIER approved.
JP: So: what can owners of DI powered cars do to prevent the buildup of valve gunk?
GB: Using the correct grades of TOP TIER approved gasoline and Dexos-approved engine oil as recommended in the vehicle owner's manual will go a long way to ensure that intake valves are as clean and free from deposits as they can be, for as long as possible.
JP: Are valve-gunk related issues, if present, covered by warranty?
GB: The warranty covers repairs to correct any vehicle defect related to materials or workmanship occurring during the warranty period. Damage caused by failure to follow the recommended maintenance schedule intervals and/or failure to use or maintain proper fluids, or maintain fluids between recommended maintenance intervals, fuel, lubricants, or refrigerants recommended in the owner manual, is not covered.