I got the Haas minimill coolant tank all cleaned up today and refilled it with the fresh!
Part of this process involved cleaning out the pump, which consisted of running several gallons of warm-hot water through the entire system to clear out any leftover debris or coolant. I accomplished this by taking an empty plastic bin and filling it with clean water, lowered the pump inside it, and let it run for a few minutes to flush everything out.
Removing the coolant and chips from the machine's bed was the difficult part and took me a while to figure out how to do it. Since this is an older machine, it doesn't have as many fancy features, like an access panel or easily accessible hatches to perform coolant maintenance. So I was subjected to crawling on my knees with an outstretched am and a wide range of long objects to push as much of the grit toward me.
I eventually cobbled together a method of using a long reach chip scooper to bring the bulk of the junk toward me, then using an (I am ashamed for this) t-square to get the chips from the very back out. I then took advantage of many old shop towels, which I used to suck up as much of the remaining liquid until it was fairly dry. Finally, I used a mop-like cleaner to pull the last remaining sludge from the back corners that the other tools couldn't reach.
Once the underside was as clean as it could be without investing a ton more time, I poured the new coolant into the machine. Finding the right ratio of coolant to water was the difficult part, and I'm shocked the company doesn't have the ratio printed on the side of the bucket. But after doing a bit of research, I found the correct coolant-to-water ratio (4-10%) and eyeballed each bucket. When there were only 5 gallons left to go, I used a refractometer (a tool that measures the water content in liquids) and measured my new coolant against what was recommended, and I felt right inside the gate of 6.4-12.0%.
There aren't many great resources out there that explain how the coolant ratio work, so I had to jump around to several sites to get the gist of it. From what I understand, each coolant type has its own ratio, but many are very similar and don't need to be spot on. Plus, over time, the water evaporates, so the coolant becomes more concentrated. When you add more to the machine, you have to keep adding less and less coolant per bucket so you can compensate for the concentrate.