While it might not be the most common car on the road in America, the VW Passat is one of the world's all-time favorite mid-sized sedans. Even before it became the third-best-selling car in Germany in 2012 -- behind the Volkswagen Jetta and Golf -- the Passat enjoyed a reputation as a generally efficient, sturdy and reliable family car. Sometimes, though, little things do go wrong -- as is the case with stuck oil filler caps.
The oil filler caps on gas engines are generally very easy to remove; simply turn the cap a quarter-turn counterclockwise, and pull it off the engine. The oil fill caps on VW diesel TDI engines of this era are a different matter though; they're well-known to stick in the filler hole. The reasons why aren't entirely clear, but it likely has to do with the O-ring on the cap seizing against the mating surface on the engine. Owners have tried many things, but the general consensus is that only metal, strap-type oil filter wrenches have the traction and gripping torque necessary to grasp the filler cap and twist it counterclockwise. Many have tried removing the cap with cheaper nylon strap oil filter wrenches, but these will generally slip before breaking the cap loose. Once you've used a metal strap wrench to get it off, you can ease future removal by thoroughly lubricating the O-ring with either standard engine oil or a much thicker 90W gear oil.
