The risks of changing the oil in a high-speed automatic transmission

How many times to change the oil in an automatic gearbox, perhaps we already have enough put it straight. We get a lot of questions and comments under the videos saying that changing the lubricant after such a portion of kilometers did not benefit the transmission and on the contrary, it left shortly after the exchange. That is why we decided to dedicate this topic and discuss it with an expert who has already repaired several thousand automatic transmissions.

Over time, the oil stops working

First of all, what oil does when it is in an automatic transmission let’s say 5 years and during that time, the car will find, for example, those 300,000 kilometers. During the first thousands of kilometers a certain operating clearance will be created, where the greatest friction will occur, wear will occur, but all the metal particles thus created will be captured by filters, or magnets. But the car continues to run, the oil goes through heating and cooling cycles, and more and more impurities enter it. Somewhere about 100,000 kilometers it certainly doesn’t look like the lube it was in the beginning. On the contrary, it is black and begins to be filled with non-magnetic abrasions, which is especially noticeable in DSG reducerswhich have connectors.

As time goes by, like that the filters stop workingeven the magnets are already so covered with metal filings that they do not work and the lubricant thickens. The hydraulics are also affected (they are always planetary gearboxes with hydroconverter), which begins to show some pressure drops, but the denser oil paradoxically partially compensates for this. The control unit gradually adjusts the limit values, everything seems to work fine.

A replacement transmission rarely arrives

Time will pass, the car will get on those 300,000 kilometers and a major or minor problem begins to manifest itself with the change. Either the engine has to rev up or it takes longer than the shift to shift, but in the extreme it can too enter emergency mode, if the reassignment does not happen at all. The owner has the oil changed, the service will do, but the car does not come home. How come? Since the new lubricant has the exact specifications it should have, it is therefore thinner than the old, which was full of impurities and thickened. However, it made up for any loss of hydraulics, so the whole system could still work somehow. New oil it cannot compensate, it’s too rare for that and doesn’t even have to be in first gear, it’s just “arrived” in the gearbox. It’s an unlikely scenario, but it happens. But usually with well-functioning gearboxes no problem after replacement.

After the exchange, the car comes to life

Then there is an even more optimistic option: the gearbox starts up again work as it should. This is if the hydraulics are fine, but the old oil is already too thick for it. Replacement takes time, the system is cleaned and everything works almost like new. It’s a blast a bit of a lottery and no service can tell you exactly what will follow after such a delayed exchange. By the way, it works in a similar way iu manual gearboxeswhere, for example, sometimes bad timing can be solved by changing the oil.

Myths that it is no longer worth changing an oil after a long run-in time, they really are more than a legend. It happens here and there, but most of the time the transmission comes to life with a replacement and its operation, speed change and maybe even decrease fuel consumption.

When to change the oil in an automatic transmission?

It is generally recommended range 30-60 thousand depending on the manufacturer and type of transmission. But it is ideal to change the oil with a flush, this means that the service is connected to the transmission circuit and it happens in fact that the old oil is used up and replaced with new oil. If someone does not change with washing, it is not optimal, but it is better than not changing the lubricant in the car at all.