Transmission fluid and engine oil are something different. Engine oil is thicker, and it is more to lubricate. Meanwhile transmission fluid (ATF) is not only a lubricant, but also a fluid to operate the transmission directly (such as hydraulic fluid).
Then what if I accidentally pour ATF into the engine? is it dangerous? What should I do ?
First, if this really happened, don't panic.
Indeed, ATF is not designed as a motor oil that lubricates the engine. But if you just pour ATF into the engine without starting the engine, it shouldn't be dangerous.
1. How much fluid are you pouring
If you fill the fluid with a small volume (a few milliliters), the fluid will mix with motor oil and it's not too dangerous.
But if you pour up to 1 liter or more, then you have to drain the engine oil to get the fluid out.
Some mechanics use ATF as an addition to cleaning engine components. This is because ATF has more detergent substances. So it's even better to descale the components.
2. Before draining, wait for the oil to settle into the oil pan
If you are worried about the condition of the engine, you can drain the engine oil that has been mixed with ATF.
However, before draining the oil, you have to wait for the fluid to accumulate in the oil pan. When we pour the fluid, the fluid will attached on the gap between engine part. We need to wait it so the fluid down to the oil pan.
The trick is to wait for about 20 minutes, the oil in the oil line will go down and collect in the oil pan.
After that you can drain the oil.
What if the engine is already started?
It is possible that the engine will make a rough sound, immediately stop the engine and do as above. Drain the oil, replace it with the appropriate oil.
But because it is circulating, you also have to change the filter oil.
In conclusion, you don't need to worry too much about this kind of problem. ATF and motor oil are different, but both of them have function as lubricants.
So when applied to the engine, it is not too dangerous as long as the engine is running in a short time.
As I said above, this ATF has more detergent substances. So it's better in terms of cleaning the scale that sticks to the components.
This makes ATF used as material for engine flushing often before changing oil.
You don't need to follow this method, because we don't know if the engine condition is suitable when applied with ATF.
You can use an engine flush, this is a special product to descale the engine before changing the oil. Of course, this method is safer because it is made from materials that are safe for engine components.