Not the best of ideas. You will have an unknown quantity of water remaining and it will take some effort to get the coolant to water ratio right. Today's coolants last so long and the system tends to require service of some sort frequently enough that not getting it all out is not a problem. 
What is important is to use distilled or otherwise mineral free water. For ease I just use the pre-mixed coolants now. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Dan N
Sent: Monday, June 29, 2015 7:44 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Coolant Draining

To purge the coolant in the engine I would fill the whole system with plain water, run it a few minutes then flush it again...

now you have a clean system ready to be filled with antifreeze...

On Mon, Jun 29, 2015 at 4:34 PM, John Goubeaux <john@ucsb.edu> wrote:

> Does someone know how much coolant stays in the engine IF one does NOT 
> pull the plugs on the engine water-jackets when doing a coolant replace ?
>
> I'm curious as I replaced the long coolant pipes and most of the big 
> hoses/ heater hoses as well , so pretty much all the coolant drained 
> out , save for what's in the engine, wondering IF it is worth getting 
> every last drop out ?
>
> Thanks  ..
>
> -john
>