[David_Vasha]

After countless research on the topic with not much to show, I decided to pull the trigger and get this DIY done. I've got to say, after doing it through this method I can finally say that I got 100% of my old antifreeze out of the system. The reason I can confirm this is because whoever had the car before me put green coolant! Which we all know is a big no no.

USEFUL INFO: The N55 model engine uses 10 liters of coolant.

Furthermore, the tools you will need;

- [ ] Common sense (very vital here)
- [ ] A hose that is long enough to reach the vent hose all the way to your designated bucket
- [ ] 6 or 7 gallons of distilled water
- [ ] 2 gallons of OEM BMW non-diluted antifreeze
- [ ] A bucket(s)
- [ ] A couple of rags or towels

Essentially how the cooling system works is that it is circulated (obviously). The vent hose that connects to the reservoir is basically the return line in this case. The coolant passes through the entire system and returns to the reservoir through this single hose.


1. Release the vent hose from the coolant reservoir by prying the metal clip up with a small flathead. Then remove the hose by gently pressing it off the nipple of the reservoir.
2. Now get your hose, preferably a clear one to monitor the fluid coming out, and find a way to get the vent hose and the hose you're using to connect securely so that coolant doesn't leak out. The best way to do this is to have a hose with a wider diameter than the vent hose. Mine wasn't larger in diameter so I used tape and wrapped it in a microfiber towel to control any leaks. This worked well too.
3. With the cap off the reservoir, get in the car and turn the heat to max with the lowest fan speed. Also turn off The AUTO, AC, and other functions.
4. Start the car.
5. While the car is running you want to make sure the reservoir doesn't run empty and keep it filled with distilled water at all times
6. Monitor the fluid coming out of the hose. You will know that all of the old coolant is gone when the fluid in the hose runs clear.
7. With the car still on and running fill the car with the BMW coolant. You don't need to dilute it because the system is full of distilled water, this mixing with it in the system. My logic was that since the car uses 10 liters of coolant, and I filled the car with distilled water entirely, it's safe to say I would need to put in 5 liters of BMW coolant. If you feel that this method is faulty, just monitor the fluid that comes and make sure the mix is how you like it.
8. By the end of this, you should see the blue BMW coolant mix coming out. At this point you can shut the car off and insert the vent hose back into the reservoir tank.
9. This step isn't necessary in my opinion, but just to make sure there are no air pockets in the system, I run the BMW coolant bleed procedure which is basically having the car in accessory mode and holding down the gas pedal for approximately 10 seconds. You know it's working when the vent hose has coolant coming out of it. The reason I say this isn't really necessary is because you never really introduce any air into the cooling system like a typical fluid drain and refill situation would. As long as you keep the coolant reservoir filled you should be fine and dandy.

With that said, always be care not to overheat your engine when doing this. If it does, something is wrong. Yours shouldn't overheat in this procedure as long as it is filled with liquid. That is your priority.