Why don't 4S shops use circulating machines to change transmission oil?

[McJohn]

Because the process requires a large amount of transmission fluid, which is costly and time-consuming. There are three methods to change transmission oil: 1. Gravity oil change: Similar to changing engine oil, this method is the most convenient and economical, generally requiring only 3 to 5 liters of transmission oil. The disadvantage is that gravity draining is not thorough, removing only about one-third of the original oil. 2. Circulating machine oil change: A transmission circulating machine is connected to the transmission's oil circuit interface, with new oil added inside the machine to push out the old oil from the transmission. This method requires about 12 liters or even more transmission oil. The more oil used, the cleaner the transmission becomes. The advantage is thorough cleaning, while the disadvantage is that it takes more time. 3. Removing the transmission oil pan for oil change: The advantage is that the transmission oil filter can be cleaned, and the oil change is relatively thorough.

[JulianaRose]

Having worked as a car mechanic for over a decade, I often chat with 4S shop technicians about this. The transmission fluid exchange machine sounds fancy, but shops actually have their own calculations: First, labor time is too precious – the machine takes 40 minutes per job, while gravity drainage just requires loosening a drain plug and finishes in 15 minutes, allowing three more cars to be serviced in the same bay. Then there's equipment cost – imported exchange machines start at 40,000-50,000 yuan, whereas gravity changes just need an oil pan. Risk is another factor – older cars with sludge buildup may have valve bodies clogged by high-pressure flushing. Last year our shop encountered a case where error codes appeared after machine flushing, ultimately requiring us to replace the customer's entire valve body assembly at our cost. That's why 4S shops prefer conservative methods – after all, manufacturer maintenance manuals specify gravity changes, and following standard procedures is the safest approach.

[EllaAnn]

Last time when I accompanied my friend to the 4S shop for maintenance, I specifically asked about this. The workshop supervisor gave a very practical answer: 90% of family cars don't need a flushing machine at all. Modern transmissions are designed with high precision, like Volkswagen's DSG, which doesn't even have a filler port and can only rely on gravity for oil changes. Moreover, the manufacturer-matched transmission oil is precisely calibrated, and a 4-liter gravity change is completely sufficient. A flushing machine requires at least 12 liters of oil, and just the material cost is over 500 yuan more expensive, which car owners find too costly and may complain about. The key point is that for many car models, the filter is located on the oil pan, and a gravity change conveniently allows for replacing the filter screen at the same time, which a flushing machine can't do. Ultimately, 4S shops have to consider the financial affordability of the majority of car owners.

[MaggieRose]

I have a ten-year-old car and have had its transmission fluid replaced at both dealerships and independent repair shops. A technician privately told me that the flush machine works well for new cars, but for vehicles with over 80,000 kilometers, it might backfire. Metal particles from the old oil, which originally settled in the oil pan, can be flushed into the solenoid valves under high pressure. Last year, a German brand's dealership caused transmission stuttering by using a flush machine, and the manufacturer even issued a technical bulletin. Nowadays, dealerships prefer the gravity drain method along with a filter replacement package—it's safer, allows them to profit from parts sales, and customers are more willing to accept the price of just over a thousand yuan.