I noticed that effect as well quite a while ago in a Mitsubishi 2.8 L that had started consuming coolant. It also did wonders for cleaning carbon deposits off the cylinder head; it was very easy to see with the head off which cylinder was leaking.

 

Wish i had that too. Coolant injection sounds cool. How power changed with that coolant? Worse , better?

 

Indiscernible change - we're talking a small amount of water into one cylinder, after all.

But it worked pretty well for this engine:

The Spitfire Society - Technical - Spitfre | The Spitfire Society

 

My 2cents....modern vehicles can be tuned for better fuel economy but at the trade off is higher emissions. Cars are tuned to maximize catalytic converter efficiency for emissions purposes. These leads to them running a bit more rich I believe than they need to be. Anyways, with coolant mixing in the 02 sensor readings were probably off and the car was probably running a little lean. Good for MPG's, bad for emissions.

 

The target AFRs also have a lot to do with the combustion byproducts as well. Ideally, we'd get CO2, H2O and heat from breaking down the fuel during combustion. However, it we run too hot or too cold (or incomplete burns, etc), we get some nasty byproducts such as partially broken HC chains, NOx, and CO.

Running lean also creates more heat (more fuel+more oxidizer=more heat+more power). In modern engines, we use fuel to also act as a cooling agent WHILE heating the air/fuel mix to help combustion. If we ran a modern, mostly aluminum engine at 1500F constant temperatures (from exhaust gases), things start to become.... soft.

Water (or coolant injection) in this case is a nice "volume expander". Water (and water-based compounds) can expand exponentially when heated (like water steam can expand to 200x it's liquid water's previous volume). This increase in pressure translates to more force, substituting fuel explosion as steam explosion. This in turn uses less fuel for the same result.

Anywho, the fuel economy may suffer slightly, but this is a case of "killing the calf to save the herd".