How to flush coolant without diluting?
 

Honda only sells Type 2 coolant in a 50/50 mixture, and not as a concentrate. I need to replace my radiator and I'd like to flush out all of the old coolant, however if I flush it out with distilled water, the coolant will be too diluted. How does everyone flush out their coolant without lowering the coolant concentration?

I buy several gallons of coolant.

If you want to be anal about it, drain and fill a couple of times with the new coolant. There will be an insignificant amount of remaining old coolant mixed in. The good news is that this coolant is very robust so the small amount of old coolant is not all that bad.

There is very little leftover when draining. I did exactly what you're worried about, and didn't have issue.

if you're concerned, put some shop air thru the system to force any fluid out the bottom of the rad.

really, no need to flush/reflush etc. Use OEM Honda coolant.
darcy

I once have opend the coolant drain bolt at the engine block to flush all coolant. In my opinion, it was a waste of time because there was very little coolant flowing out. Maybe a longdrink glass full - 0.2 Liters / Quarts. Really, not much.
So, dont waste a thougth about it. You will add about 8 liters of fresh coolant, this mixes with the remaining 0.2 liters in the block. Thats 2.5% roughly calculated.

Honda doesn't seem concerned about any residual antifreeze. Unless you do what the Service Manual calls an engine overhaul there's 1.1L (0.29gal) of horrible, nasty, old, stale antifreeze that ain't gonna come out. My math indicates that's 14% of the total capacity of 7.6L. (1.1 ÷ 7.6 = 0.14).

Flush with distilled water several times and that 14% is now is just water diluting the mixture from 50% to roughly 43% antifreeze thus reducing the boiling point. Maybe bump the radiator cap pressure up from 1.1bar to 1.2 or 1.3?

Enough trivial math for me right now. :) I just drain and refill it every 5 years or 60,000 miles. First antifreeze change was at 10 years. #2 at 15, #3 coming up next year for my 2006 car.

-- Chuck

This is what I did. Just bought some extea gallons of grocery store distilled water (NOT drinking water, water for clothes iron, etc). Its cheap. I just flushed with water more than once, so all the leftover was simply water. Didn't worry about the dilution, freeze point.

It was a slow morning and the math exercise made it more interesting. :) I stopped before computing the new boiling point of the diluted antifreeze at 1.2 and 1.3bar. Anyone?

-- Chuck

Shop air through the firewall bleeder to get any remaining coolant out.