The trapping ability of the Volkswagen oil filter is why the oil can be left in the engine for 3,000 or more miles with little to no wear on the moving components on the interior of the engine. Once that mileage point is exceeded, the saturation level of the paper element in the oil filter is near its limits and should be replaced on your Volkswagen. As a safety measure, each Volkswagen oil filter has a built-in relief valve. This will allow the oil to bypass the paper filter element if it has reached the saturation level. This way, oil will be able to continue to flow to the vital moving engine components even though it is slightly dirty and partially filled with contaminants. The owner of a Volkswagen wants to seldom, if ever, utilize this fail-safe device if they desire to have their engine last for an extended period of time. The contaminants in the oil are from the combustion of the fuel where small carbon atoms are released into the oil. It is the purpose of the oil filter to remove these minute particulates so the purest level of oil will continue to flow through the engine. In addition to the combustion deposits, very tiny metal shavings are also present and can pose a danger to your bearings and internals. The reason for an oil change is not to replace worn out oil but so a new oil filter can be put into place on the engine. This is something most Volkswagen owners are unaware of. If just the oil is changed, the amount of clean oil arriving at the bearings and cylinder walls will be diminished very fast once the engine is running. It is the oil filter and not the oil that is in need of replacing so the engine will last for thousands and thousands of miles like it should.