There is no fixed answer to how often a sewage mixer needs to add lubricating oil, because it depends on a number of factors, including the frequency of use of the equipment, working conditions, the type and quality of lubricating oil and so on. Here are some general guidelines and suggestions:

First, the general range of lubricating oil replacement cycle

1. New machine first run:

- After 200-300 hours of operation of the new machine, it is usually necessary to replace the reducer lubricating oil and clean the internal oil. This is to ensure that the new machine can operate normally after the run-in period and extend the service life of the equipment. 

2. Normal use period:

- During normal use, the replacement cycle of lubricating oil may be extended to six months to once a year, depending on the use of the equipment. Some recommendations point out that it is more common to change the lubricant every six months, especially for submersible mixers. 

There are also some more specific recommendations that indicate that the replacement cycle of lubricating oil can be determined according to the working time of the equipment, generally 1000-2000 hours, or according to the recommendation of the equipment manufacturer and the actual quality of the lubricating oil. 

Second, the factors that affect the lubricating oil replacement cycle

1. Frequency of equipment use:

- If the sewage mixer is used frequently and runs for a long time every day, the replacement cycle of lubricating oil needs to be shortened accordingly. Because the high frequency of use will accelerate the aging and pollution of lubricating oil. 

2. Working conditions:

- The working conditions of the equipment will also affect the replacement cycle of the lubricating oil. Mixers that work in harsh environments such as high temperature, humidity, and corrosion may have a shorter replacement cycle for lubricating oil. 

3. Lubricating oil type and quality:

- Different types and qualities of lubricating oil have different service life and replacement cycles. High-quality lubricants usually have a longer service life and better lubrication, so the replacement cycle can be relatively extended. 

Third, other precautions

1. Check regularly:

- In addition to changing the lubricating oil according to a fixed cycle, the lubrication system of the mixer should be checked regularly, including the oil level, color, odor and impurity content of the lubricating oil. If the lubricating oil is found to be deteriorated or seriously polluted, it should be replaced in time. 

2. Add lubricating oil:

- Between two lubricating oil changes, if the amount of lubricating oil is found to be insufficient, it should be replenished in time to ensure that the equipment is fully lubricated. 

3. Follow manufacturer recommendations:

- The most important thing is to follow the maintenance and maintenance recommendations of the equipment manufacturer. Manufacturers usually determine the replacement cycle of lubricating oil and other maintenance measures according to the specific design and use conditions of the equipment. 

In summary, the lubricating oil replacement cycle of the sewage mixer should be determined according to the frequency of use, working conditions, lubricating oil type and quality of the equipment. Under normal use, it is common to replace the lubricating oil every six months to a year, but the specific cycle needs to be adjusted according to the recommendations of the equipment manufacturer and the actual situation.