An engine does not need to be full of sludge to create havoc with the VVT/variable timing. The beauty of Auto-Rx is that it slowly and methodically dissolves sludge, without breaking free large deposits that can create problems. This is why Auto-Rx is designed to dissolve deposits slowly. The filter is there only to collect materials that are not dissolved. It only makes sense that engine deposits build over time, and that they should be removed over time as well. That is in contrast to quick flush products that break large chunks of contaminants free.
