[murcod]

Make sure you've got the cabin heat turn up inside so the heater core gets flushed/ drained too. I usually wait until the engine is warm before draining so then the thermostat is definitely open. You need to be careful when draining then though, so you don't get scalded. Wait until the engine has cooled a bit before refilling.

Buy coolant concentrate too - not premixed. That way you should be able to add the 50% amount even when the whole system can't be emptied.

Parking on a slope may help drain more out.

 

[murcod]

I might be mistaken, but don't the newer heater cores flow coolant all the time now, and just the blend door opens to allow heat in the cabin or not??...The reason I think that is I did not have to run my engine more than a minute or 2 when cold to clear my old coolant when draining and refilling, and when finished, I had no remnants of the old orange color at all...

I had a quick look in the workshop manual- the 1.6l appears to have a variable flow control to the heater, the 2.0l doesn't appear to and the 1.5l isn't covered by the workshop manual I've got.

 

[murcod]

Call me crazy, how do you check for 50/50 if you're adding concentrate into the system directly, that is now sealed/filled with water? Just guess on capacity?

All I've ever done is look up the capacity, then add the required amount of concentrate first. Top up the rest with distilled water.