Why doesn't all the coolant come out during drain and fill?

I asked this question in the coolant drain and fill thread, but it was quickly overwhelmed buy a debate on types of coolants and I never really got an answer.

When I drained and filled coolant system I only got out a little less than two gallons. I have seen others had a similar experience, but did not see any explanation why all of the coolant fails to drain. Does anybody know why what comes out doesn't match the capacity of the system (for some people)? Is there really two quarts or more of the coolant that doesn't come out? If I flushed with distilled water would I ever be able to get it all out? I emptied all 3 drains and the truck was level (I didn't remove a wheel). Cap was off. I opened-drained-closed each drain one at a time in the following order - radiator, driver's side, passengers side. Thanks.

 

Because there is coolant either below the drain level or not all of the jackets flow to the drain level.

You'll never remove everything. But you can replace everything. As you keep filling/draining residual is diluted/removed. Eventually all residual will be gone, but there will be a quantity of whatever you were filling with left.

Over the years I typically just drain/fill with water/circulate about 3x. If things are still looking a bit yucky, I fill with pure water (yes, tap water. shame on me) and drive/dump/fill every day for a week. That usually does as good as it's going to get.

Then I drain and fill with appropriate coolant/distilled water mix. Work to burp, monitor and top as needed over a couple of days and call it good.

The small amount of tap water left in the system is not enough to cause concern.

 

This isn't rocket science

I only flush out once unless lots of stuff comes out

drain best you can and plug up
add distilled water in, run for a few and dump again
repeat as many times as you feel its needs or run out of money

add in the correct amount of 100% coolant and then top off with distilled water

 

I also replaced the thermostat and think Rocket Science may have been easier than accessing the nut closest to the engine block.

I used the Toyota SLLC so if I had rinsed with distilled water and then added coolant, 20% of capacity would have been distilled water and the rest the Toyota premix. That doesn't seem right.

Also seems weird that some people get all 10 quarts out and others report getting 8 or less.

 

don't use premix

 

Yep Knotty. Next Time. Unless somebody tells me how to get it all out...and then I'll use the SLLC again (since I have an extra jug now).

 

As said, it's because the coolant in the engine block is below the lower radiator hose connection point; this is typical on every vehicle I've worked on. There are usually coolant drain plug(s) on the block if you want to drain it all but sometimes they can't be readily accessed. When they can't be accessed, I flush with water a few times, close everything up, then add a little more than half the specified system capacity with straight coolant, then add water for a ~50/50 mix. Then run and check the coolant. I have the Prestone coolant tester that shows the % water and coolant, and it's pretty accurate, but you should calibrate it yourself with a fresh 50/50 mix and compare it to what it reads.

 

That nut was such a pain in the ass...especially if you drop it lol