Welly wrote:C4 1.6D
While the C4 is a wonderful car to drive, and the 1.6 HDI is a gutsy little engine, it has a severe design flaw, and I'm not sure if an official fix has been made yet.
The oil feed line to the turbo goes through a banjo bolt, which incorporates a tiny metal mesh filter. This is meant to prevent any particulates in the oil from reaching the turbo and fouling the bearing. This is not a design flaw in itself, but unfortunately, the oil pan is designed in such a way that not all of the oil in the pan is extracted during a normal oil change. The drain hole simply isn't at the lowest point. This leaves a significant amount of particulates in the oil, which will clog the banjo bolt filter over time and starve the turbo of oil.
The solution to this is to drop and clean the oil pan on every oil change, which is obviously both expensive and time-consuming. The alternative is to fit an oil pan with a better design. I don't know what the situation is in the UK, but in Scandinavia, the Mekonomen service chain have marketed a redesigned oil pan that solved the problem. Another cheaper solution is to remove the filter from the banjo bolt, at the risk of shortening the life of the turbo.