Castrol® GTX® 5W-20 is a synthetic blend motor oil with a double-action formula proven to clean away the sludge that can block engine oilways* and help prevent new sludge formation.
Sludge is a thick, tar like substance caused by severe driving conditions such as heavy traffic, poor fuel quality, harsh driving conditions and exceeding oil change intervals. Sludge can block your engine's vital oilways like cholesterol and if untreated, can rob an engine of its power and ultimately its life.

* When tested in engines with a high level of sludge