My science project:
Just to be provoctative, I've constructed a little experiment. Try it for yourself.
Tools:
Electric stovetop, heated to max temperature
Aluminum pie pan
Water
Ethlyene Glycol AF
Water Wetter
Dishwashing soap
Procedure:
The first step is to put a pound of room temperature water in the pie pan and place it on the stove. Time how long it takes to boil.
Boiling condition is identified when the solution reaches a plateau temperature. Temps were observed at 15 second intervals, because I was doing this by hand. Temps in degrees F, because that was the thermometer I had handy. I did each test twice, to check my times.
Repeat with a mixture of water/water wetter, water/glycol (50%)/water wetter, water/glycol (50%), water/diswashing soap.
Rationale:
The stovetop represents a hot engine component, the coolant is the coolant, and the air/coolant interface is the radiator. The mass of the pie tin is small enough to be disregarded. The longer the coolant can go without boiling, the more heat it can transfer. Lots of differences between this model and a real cooling system (thanks in advance for pointing them out), but it's just a quick and dirty.
Results:
From best to worst, time is in seconds:
(time, plateau temperature, solution)
180 212 Water/Water Wetter
180 225 Water/Glycol/Water Wetter
165 225 Water/Glycol
150 212 Water/soap
120 212 Water
Test conditions: 70F ambient, elevation 100M,stovetop temp 800F.
Observations:
Water wetter seems to do what they advertise. Put a few drops in a boiling pan of water, and the vapor bubbles disappear, replaced by no bubbles or streams of tiny bubbles. Clearly, more liquid is in contact with the pan.
Diswashing soap was less effective, and foamed a bit. I think that liquid soap is partly water, which may explain it's lack of effectiveness.
Conclusions:
It works in the pan, but can't assume it works in the car. I doubt that observed temperature would change, unless your car was very close to overheating in normal service. But hot spots would probably be reduced or eliminated. We can debate the value, but I can't seen any harm.