Power Up Heavy Duty CF4 series is more than just oil. it's liquid engineering that protects against problems, like sludge, that your engine faces every day. Severe driving conditions such as every day stop-and-go/stop-start traffic, harsh weather conditions and extended drain intervals, can all cause the build-up of a thick, tar-like substance called sludge. You can't see this sludge build-up but it can damage your engine's performance and cause premature engine failure. Protect your car from harmful sludge build-up.