SLLC Crystals

This has been a curiosity of mine for a while now, so I figured I'd post the story and see what anyone else thinks. I have already searched the forum extensively and can find only one mention. Years ago I purchased a gallon of the Toyota SLLC 50/50 pre-diluted antifreeze to use for top-up. I have about a half gallon of it left in the original container that is kept in an outdoor storage area but tightly capped. I'm not sure how old this stuff is or whether there is a shelf life to be concerned about.

Several years ago I was going to top up the overflow tank in my 2011 Gen III. I think it might have been in early Spring when it was a little cold outside, but I don't think that had anything to do with it. I agitated the container and poured out a quantity of SLLC into a smaller container. I noticed it looked a little strange. There was what appeared to be a layer of long, branching pink crystals floating on the top of the pink fluid. I held the container up to the light and shook it a bit, and the crystals appeared to form and dissolve with the agitation. I went ahead and poured this curious solution into the overflow tank and brought it up to full. I looked closely at the fluid in the overflow tank afterward and didn't see any of those crystals.

Today I was doing a maintenance check on my 2021 Gen IV and noticed both the engine coolant overflow tank and the inverter coolant tank were a little low. It has been cooling off here for the past week or so. So I get out my half gallon of SLLC and pour some out into another container, and there are those crystals again. Ambient air temperature today was around 80 F. And when I poured it into the coolant tanks the crystals were gone. Any ideas what is causing this?

 

I've done some reading. Still can't find an exact reference, but I found plenty of chemistry discussions concerning crystallization states of organic acids. The main ingredient in Super Long Life Coolant is something called HOAT. Hybrid Organic Acid Technology. Not my area of expertise, but interesting nonetheless. There is an analog perhaps in meteorology in reference to specific cloud temperature regions conducive to something called dendritic growth. This is a type of ice crystallization at certain temperature and moisture variables leading to rapid crystal formation. Think of winter weather heavy snow. This function still requires a seed or nucleation site to get things started, whereas the crystal formation in this antifreeze is spontaneous and likely due in part to concentration of various chemicals and a lack of contaminants to act as growth seeds. I'm not going to worry about it, unless anyone else has some ideas.