BMW recommends 60% antifreeze for additional freeze protection;
BMW recommends filling the cooling system for protection against freezing down to -34°F (-37°C). This means an antifreeze ratio of 50% antifreeze and 50% water. In severely cold areas, the antifreeze can be increased to 60%, which provides freezing protection down to -62°F (-52°C). Do not exceed a 60% ratio of antifreeze. The specified antifreeze ratio is important, since an insufficient amount would impair anti-freezing and corrosion, inhibiting protection. An excessive amount would not improve freezing protection, but would instead reduce freezing protection. At all times, the antifreeze and water should be pre-mixed before pouring into the engine. If pre-mixing is not performed, damage will occur to the water pump assembly.
One thing not yet mentioned is the water. I strongly urge using distilled water, about $1/gallon at any grocery store. Tapwater, whether well or town, can contain minerals and other elements that while safe to drink can cause problems in a cooling system.
For estimating the volume drained, I’d drain into a convenient sized drain pan, then pour from the drain pan using a big funnel into a 1 gallon empty Clorox jug or such. Repeat as necessary. That’d be accurate to 1/4 gallon. Convert to liters, done.
If you want to save yourself some clean-up time, place a plastic garbage bag into the drain pan first. Then just throw the garbage bag away when done.
You might appreciate this link defining the difference between deionized water and distilled water. Both are much better than tap water, but the distilled water is more pure. https://van.physics.illinois.edu/qa/listing.php?id=1743
But I don’t think is worse for the actual engine. If I recall, the deionized removes the stuff that hurts radiators and cooling system. It just keeps random remanants that do not negatively affect correct?
When I flush the toilet I expect that enough incoming water totally expells and replaces the contents of the bowl. I suspect that it requires 3 times the normal capacity of the bowl to so. And if 30 liters of fresh water were quickly flushed through the cooling system of an 8 liter capacity cooling system which was then drained I would expect that there would be an insignificant amount of clean water left in various low areas of the cooling system but after adding 4 liters of coolant and then properly topping off and burping the system all would be in order.
I vowed to stay out of this but can’t help myself. I have always had to add the full strength back in in order to get enough in for a 50/50 mix. If I would have added pre-mixed, I wouldn’t be able to get enough in the system to get to the 50/50 solution. But I’ve never taken the block plugs out, just the radiator and lower hose. So I guess once you get it all to clear water, I would add the undiluted quantity to give you the 60/40, then fill the rest up with the water. And good luck to you at those temperatures. It’s not necessarily cracking the block but the slush can restrict circulation in the hoses and cause over-heating (in my limited experience anyway).
I have never pre-mixed, I pour in half the capacity and add water after. It is usually above 70 F here so the thermostat opens plenty during a road test and the coolant mixes, if it was -20 F I would probably pre-mix.
I’ve always used distilled and never actually looked into it, but that’s probably true. Mineral deposits are the biggest problem with tap water and deionized water has these removed.
I’ve never been able to get the brass drain plugs off the aluminum block of my 02 truck even after a year of ownership. Ended up breaking the tip off on one when attempting to take it off the block when cold and thankfully it wasn’t enough to cause a leak, so from that point forward I just drain the radiator once, fill, drive for a week and repeat. Isn’t the best method, but it works.
That can get a little messy for me, so I just open the drain cock on the radiator and then open the cap on top to let in the air and empty it quickly in a 5 gallon bucket. Thankfully the bucket is just at the right height right below the radiator. Last time I did it with the hose to change out the thermostat, I overshot the bucket! lol
Nice if you’ve got a pet cock on the radiator but not all of them have them anymore. So about all you can do is pull the hose and have a pan ready. Some don’t have either a drain or a cap to fill too. My Olds required pellets be crushed and added so I ended up adding them and the fluid through the upper hose first and then finishing off with the reservoir.
