Engine sludge is usually caused by infrequent oil changes or using way too thicker oil grades which this engine is not designed for.
You may fix the oil reduction issue with engine flush. Sometimes it works and in other cases it doesn't when there's any physical damage in the engine. If you plan to flush the engine, make sure you flush it again with any cheap new oil to completely drain the flush chemical.
You don't need to use expensive oils. You can stick to mainstream oils like havoline, total, pso, zic, kixx
