Cro

I just ended up doing a coolant flush as the old coolant appeared very dirty and I thought as I was planning to change the heater control valve I'd do a flush just for peace of mind. I drained the coolant and followed with 3 flushes before the night's end. I knew that the entire system wouldn't drain and some water would be left behind but I underestimated how much would likely be left behind. I ended up using a 50/50 pre-mixed coolant but I was only able to put in around 2 gallons out of the 3 gallons the system holds. My concern is that after 3 flushes with distilled water is that there would be more water than coolant left over in the system before I refill it with the 50/50 mix. Now I'm worried that my ratio is off by a large margin as only 3.785L of the coolant would be in the system with the remaining 7.5L or so possibly being distilled water making it nearly a 30/70 or 40/60 coolant to water mix respectively depending on how much water/coolant wasn't drained out through the flush. Wondering how effective this mix would be and if I should flush the system again and use a concentrate instead to get the correct amount of coolant in. Any help/advice would be appreciated.

Heguli

Drive some so the coolant is mixed with water, then check the coolant freezing point with antifreeze refractometer. Drain some, add concentrate. Might take couple of tries to get it right.
That's how I do it.

streborx

If you're reasonably certain of your existing mix -- 1 gallon of water and 2 gallons of 50/50 coolant -- this means you currently have 2 gallons of water and 1 gallon of coolant. Converting to liters, this is about 8 liters of water and 4 liters of coolant. If you drain 3 liters of the mix, 2 liters are water and 1 liter is coolant, leaving you with 6 liters of water and 3 liters of coolant. Add 3 liters of coolant (100%, not 50/50), and this brings the mix to 6 liters of each -- the target 50/50 mix. Check the specific gravity as suggested already just to be sure.

Cro

I ended up doing the math and you also got it fairly on the dot as what I came up with (picture attached with what I came up with). Going to use a tester as another commenter suggested to make sure of the estimates I made and adjust accordingly. Thanks for the help!

BlackML550

From memory, the M273 has two purge valves, one on each side of the block to allow you to drain the water jacket. If you put your VIN in your profile I will find the WIS procedure for you.