I've tried supercooling a loop before with DICE and learned a few things.
As Witchy said earlier, take the rad out of the loop, your coolant will freeze in it and stop coolant flow. I also tried a mix of antifreeze and water, got too thick for the pump to move it and since I could not find anything else to use at the time, poured a spare bottle of 190 proof (Everclear) in the res and that did the trick.
Be sure to start off if using an open res as I do, You'll need to have the coolant being used chilled FIRST.
I was starting with a dry res and I would pour the coolant being used in, then slowly add the DICE - It creates a boiling effect as it sunlimes and could cause the same thing as a boilover that hot water could do in a pot for example. Start the system to bleedoff any air bubbles though before actually adding the DICE to the coolant. Once you see the air bubbles are gone, add the DICE.
Correct me if I'm wrong but I think it's denatured alchohol that will do the same thing and it's cheaper too.
The pieces of DICE themselves created an "Iceball" in my res that took a long time to melt away and as it did, the remaining DICE would refeeeze the water around it creating a small block of ice that lasted for sometime = Good for longer runs.
I actually had several of these blocks in it and they kept coolant temps low for sometime. Just having one or two didn't make alot of difference but having several of these going in the res did the job. Had to do some testing to see what the best "Balance" of these iceballs would be, obviously the more you have the colder your temps will be but even with the coolant treated as such, too much DICE will cause freezing problems unless the coolant simply won't freeze at DICE temps.
That wasn't the case when I was testing (The coolant would freeze but not badly) and I also noted once these were present, temps did come up but stayed low enough to do some good benching.
I had to be sure the res itself was insulated vs condensation and be sure what did drip was caught by a pigmat to control the mess - Had the res sitting on one of those for that purpose. Of course be sure your coolant lines are also insulated vs condensation and be sure any water that runs along /drips from them doesn't cause trouble.