The engine block coolant plug on a 6-cylinder is near the bottom of the engine. You will need to use a socket set and ratchet to remove the plug.
Sounds like a head gasket issue, or worse, your head could be cracked. Check your exhaust - that's probably where your coolant is going.
If you've got a REALLY big set of tools, it could be. Coolant in the engine oil is caused by one of three major things--bad head gasket, cracked head, cracked block. IOW, you'll need to do some major repairs to the car right away. If it's a great car except for the engine, and you can get the price down low enough, it might not be a bad buy. If you're buying a car so you can use it today, walk away from this one.
cracked head, cracked block Bring it in asap. Id be willing to bet you have a cracked head. If you keep driving like that you'll screw up your engine. Coolant isn't made to lubricate an engine, and your pistons and other items in your engine will pay for your driving it like that. Im surprised your car doesnt overheat. No oil additive is going to fix your cracked head, it needs to be replaced.
Remove the lower rad hose and drain, the block itself has no supplied drain. You can also use the drain petcock on the radiator lower drivers side but it is prone to leaking after use.
You need a special tester called a block check. You fill it with a special fluid and then use it to suck fumes out of the radiator . if the fluid turns yellow it means there is exhaust gasses in the coolant.
When fitting a 4G63T head onto a 4G64 block, you need to block the coolant passages that are not aligned between the two components. Specifically, you'll typically need to block the two coolant holes at the rear of the head that do not match up with the block. Additionally, you should ensure to use the appropriate gasket to prevent any leaks and ensure proper sealing. It's also important to verify that the oil passage alignment is correct to avoid engine damage.
as long as it is not the winter... then it will freeze. and never put water in a hot empty radiator or you will crack the block and you will be very sorry.
Sometimes they use that threaded drain plug location to attach a knock sensor. So if you see a knock sensor threaded into the side of the block that may be where the coolant drain is located.
You will have to remove the heads and have the block welded by a skilled welder or you may in the end have to purchase of a new block. The only other choice you have is to buy a used engine and just replace the entire engine. You can of course buy what is called a short block and use your old heads and manifolds.
use half coolant and half water
Use only BMW recommended coolant.