I have a 2012 Kia Sorento SX AWD (that's the 3.5l V6). I am following the instructions in the service manual for replacing the engine coolant, but when I unscrew the radiator drain plug I only get about 0.75 gallons of coolant out. The coolant capacity is 1.9 gallons. Even if that includes the reservoir, there is still a good amount of coolant in the engine block. I know this because when I first drained the radiator, filled it up with distilled water, ran the car until the fans kicked on and drained it again, the fluid was dark green indicating there was significant coolant left in the system after the first drain.

Has anyone run across this on this car or any others? I have seen some YouTube videos where people run the engine to activate the water pump while the radiator drain plug is open, but I am wary of running the water pump until it is dry. Additionally, the service manual seems to indicate that the all the coolant should just drain through the radiator plug.

My concern is that the water left in the system after it is flushed will dilute the 50/50 coolant mixture I add to below a safe level.

  • Welcome to Motor Vehicle Maintenance & Repair! Nov 7, 2020 at 0:15
  • stupid question but did you remove the radiator cap? Nov 7, 2020 at 11:48
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1 Answer 1


Sounds perfectly normal. I've read that, typically, you can only drain about half the coolant from a system when you empty the radiator. In my experience, among several cars, that has always been the case. You are draining less than half, but not by much.

In order to really flush the entire system, I've had to drain and fill the radiator five times. Drive the car for at least 15 minutes between each drain. Many videos on YouTube will show that five changes provide the most thorough flush. Otherwise, change it once a month until you are happy with the clarity of your coolant.

You are wise not to run the engine with the drain plug open. I've read somewhere that it could lead to disaster!

So, keep flushing. An ounce of prevention really is worth a pound of cure in the world of automobile cooling.

  • Thank you, Carguy. I think I can do the flushing part, but my concern is that after the flush, when I add new coolant back into the system, won't it be too diluted when you account for all the water in the engine block?
    – Gabriel
    Nov 9, 2020 at 21:19
  • Should I have the front of the car on ramps for this? I have been doing it with the car level.
    – Gabriel
    Nov 11, 2020 at 5:47
  • @Gabriel No, you don't need to raise the car on ramps. If you've been flushing with water and the coolant is dilute, you can check the concentration with a small tester available at any auto parts store. If it's too watery, buy concentrated coolant (not the 50/50 mix), drain some coolant, then add the concentrate and re-check with the tester until the mix is balanced.
    – Carguy
    Nov 19, 2020 at 6:52

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