“换油前在Engine和油箱里各倒半瓶”？

i did, but not exactly like what you described.  to clean injectors and whole fuel system, you can pour one full bottle of it into fuel tank prior to filling up the tank, drive the car normally until it is almost empty before refill.  to clean engine sludge - be careful with older cars it could cause leaking - before you change oil, while engine is on normal operating templerature, pour the entire bottle of it into crank case, idle for 5 minutes (check instruction), then change oil.  For most cases, engine block cleaning is not necessary unless you are sure otherwise.