Planning on doing my first coolant change and will be changing the ratio to 30/70 31/69, coolant/water, as well as Water Wetter (Houston gets hot in Feb). I'm reading people are draining 1.5 gallons out of the drain and reservoir, but FSM capacity is 9.125 quarts. Does the remaining 1/3 get stuck in the system and I need to account for that being 50/50, or should I be doing a flush to get the rest out? Also, do I need to factor in the Water Wetter volume as one of the components?

Edit: I'm at 60k miles
Edit 2: I'd be using OEM premix and distilled water.

 

I would use the blue kind & change every 2 yrs or 20k. That's my maintenance DIY schedule. I live in H-town too.

 

That seems a bit excessive for the blue stuff. Doesn't answer my question though.
I'm probably going to just do a drain/fill and replace whatever was taken out with 25% coolant mix to average it out, assuming 1.5 gal is removed, then top off with distilled water. I didn't recall water wetter changing reservoir volume when I dumped some in previously.

 

Well if you want to get close to 30/70 ratio then yes go ahead and flush the system. I would put the water wetter into your system and not the reservoir as it may damage it.

On another note that blue stuff might be your best option with the water wetter. Seeing as water boils around 212 degrees I believe and our cars can sometimes get to 220. That blue stuff boils at around maybe 265 and the mix your going for is around 235 give or take. I know you didn't ask but that's a bit close for comfort. If water gets hot it will expand . I know you want to run cooler but our cars run hot due to oil getting hot ,not the actual coolant system.
Just my 2 cents

 

Yes water boils at 212, but not in a pressurized system. With a stock cap and properly sealed system water wouldn't boil til close to 270.

As for the original question, I have a question. Why do you have the desire to go down to a 30/70 ratio? If you think it will aid in cooling you'd be wrong. Antifreeze is also coolant. Coolant absorbs heat better than water. Your best ratio for cooling would be 50/50.

 

The radiator cap is designed to relieve at 137 kPa, so a 30/70 shouldn't boil until over 260°F. Yes, the oil gets hot but additional engine cooling would help more than anything.

Well the reason was better cooling because water has a higher specific heat than glycol, therefore being better at heat transfer. "Coolant" will hold a higher temperature, but the heat transfer is slower so I'm not sure where you got your science from.


Edit: I wasn't aware of needing to open water drain plugs on the cylinder block to get the rest out. The manual refers to the engine disassembly manual, which seems a bit intimidating for basic maintenance... so I'm thinking of just the drain/fill to get the ratio, then do another the next year to get fresher coolant in.