[mrein3]

You want exactly 50-50 in your cooling system. 50-50 will get you to -40 degrees.

The proper way to fill a system is as follows:

Find your owners manual. It will tell you how much coolant your systems needs. Usually in quarts. Say it says 20 quarts.

After you flush or drain or are done with whatever you are doing, put 10 quarts of pure, undiluted anti-freeze in your system.

Top off the system with pure water.

Start the engine with the radiator cap off.

You need to "burp" the system. The level in the radiator will rise as the engine warms up so have a catch pan under your still open fill neck.

Once you see a good flow coming out of the fins inside the radiator, pour in what you caught in your catch pan and then fill the radiator to the top with water.

Install cap. Done.

Unless you are starting with a totally rebuilt system (engine, heater core, hoses, etc.) you're going to have flush water in the system. By putting half of the required anti-freeze side of the 50-50 mix in the system you know all you need is water to make it 50-50. You also need to burp it so you get all the trapped air bubbles out.

After this point, if you puke some out in the spring or fix a small leak, top off with 50-50 and you're good even for a Minnesota winter.