Herbert
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Following information obtained from another international forum on BMW and thought it would be informative.Sludge is either a breakdown of the base oil or contamination of the oil to such a high level that the oil thickens and begins to solidify or turn into a jelly-like consistency. It can be caused by a number of conditions, including: Severe service, Mechanical malfunctions which contaminate the oil or Use of Dino oil (non-synthetic oil). Assuming we all use name brand full synthetic oil, strike number three from the list.Contaminants in oil are normal, but extended oil changes allow the contaminants to reach highly concentrated levels at the same time the oil additives that fight contaminants degrade due to age. The characteristics of the oil are changed and lubrication is affected.Severe service Short trips, stop and go driving, extended idling, extended high temperature operation, towing or other severe loads, extreme cold starting and idling, which causes the engines to either run too cold or too hot. If the engine never reaches operating temperature it won’t burn off volatiles and water vapor which condense in the oil. Operating at elevated temperatures tends to thicken oil base oils (less so for synthetic).Mechanical malfunctions Causing Contaminants to Enter OilLeaky fuel injectors (gasoline), malfunctioning choke mechanisms (unburnt gases), clogged or defective PCV valve (unburnt gases), excessively worn spark plugs (soot), blow-by exhaust gases from worn valves or blow-by gasoline from worn rings, and worst of all coolant from leaking gaskets. Extended Mileage between Oil changesModern full synthetic oil is amazing, but the natural introduction of contaminants as the engine runs, even in a well tuned engine, begins to interfere with the additives and detergents contained in modern oil. Left long enough the oil will degrade and turn gel-like to the point that small passages in the engine designed to be lubricated no longer will be reached by oil as the sludge blocks opening. The still liquid oil that does reach other places is so contaminated that it is unable to create a lubricating barrier between moving parts.Quoting from a Website:Another not too often disclosed fact is that during the ILSAC or API engine tests on motor oils, the oil life is measured in HOURS, and yet only very few vehicles sold anywhere in the world have ENGINE HOUR RUN meters.The normal motor oil recommended service frequency is specified in miles or kilometers, but the motor oil life is in hours of service.Sure you can approximate how many miles you on average drive in how many hours, but if in your particular car you are stuck daily in stop and go traffic, you can easily average twice or even three times MORE hours of engine run time for the SAME distance traveled !Most people in the USA spend about 500 hours in their vehicles annually while driving from 9,000 to 15,000 miles. That is an average speed of only 18 to 30 MPH !Yet automobile industry still today equates "normal" driving with 45 MPH average, something that is almost unattainable in modern traffic unless you only drive on highways.The longest and most severe engine oil test: "Sequence VG engine test" runs for 216 hours, and if motor oil passes this test it is suitable to be licensed under the latest API and ILSAC quality classification (API SM or ILSAC GF-4) - yet that represents MAXIMUM SAFE service interval of only 3,888 miles for someone that averages 18 MPH in typical city traffic !But what if your MPH average is only 12 MPH ? That is ONLY 2,592 miles !Don’t think sludge can form in your Bimmer with BMW’s recommended 15K oil changes using Synthetic oil?http://forum.roadfly.com/threads/9530333How to know if you have sludge? 1. Examine the oil after draining from engine. Is it dark black and still pours thinly, or does it have the consistency of Elmer’s Glue? Does it smell like gasoline? Is it brownish in color? You probably are starting towards or already have sludge.2. Pull the oil pan or valve covers and have a look. Sometimes sludge will be visible through the oil fill hole.What can you do?1. Several quick oil changes (200-500 miles between changes) with extended service oil, which typically has higher levels of detergent. This may break up some sludge, but you must get it out of the engine quickly. Usually this will have only a marginal effect.2. Drop the pan and clean it. Pull the valve covers and clean as much sludge as you can off parts.3. If the damage is severe enough it may be time for a rebuild/replacement or run the engine until it dies.For older engines it is recommended that a sample of the drained oil be sent for analysis (approximately $25). This can be done every second or every third oil change. The test will analyze the oil chemistry and based on the presence of certain chemicals can indicate excessive gasoline, coolant or types of metals which can indicate wear of valves or cylinder walls. If any of these levels are excessive the first action should be searching for a cause (maybe leaking coolant gasket). If the car is older with high miles and fixing excessively worn engine parts is not economically feasible, at a minimum reducing the miles between oil changes can potentially stretch extra life out of your ailing engine. Moral of the story – Don't let your oil get to the point where sludge forms.If you want to keep your BMW running a long time change your oil every 5-6K miles maximum, or every 3K miles if you drive stop and go or do short trips frequently. Get the contaminants out of your engine and she will purr for a long time.
