Yeah, coolant was added as an option to cool combustion engines a few versions back. That means that it is a valid liquid, and all that that entails (liquid transposer, redpower pumps, iron tanks, etc.).
EDIT: Interestingly, that means that the recipe for coolant is 4 tin and a bucket of water, essentially (you surround a water cell with 4 tin and you get a coolant cell. In a transposer, you get the original cell back).
I wonder if any mod might implement that as a side-recipe (i.e. in a squeezer or still or suchlike) to get just the coolant back?
That might make getting the cells en masse quite a bit easier. Just have a tank full of coolant hooked up to a transposer, outputting to a chest/crafting system. Input cells, output product.