TEN gallons per hour ??
No wonder you ate your motor!
That is way way off.
Run the numbers.... (DT466 example)
Your cruising 60mph....and, say, 10 mpg. That is only SIX gallons of fuel per hour. And the water should only be 30% of the total, MAX. So that'd be about TWO gph needed at cruise; not TEN!
On a medium-truck, I think it'd be safe to assume (for this discussion) that one is using about half the max-HP to maintain 60mph on the flat; i.e. 100-125 hp. Since the max HP is about 250, even max-power climbing a hill would only need 4gph of water.
I think that if you work for more of a 'spray' than a mist, you will see more of a decrease in EGT's...AND an actual improvement in MPG's. It is the water that evaporates IN the cylinder which lowers the EGT's.
A fine mist which evaporates in the air-stream BEFORE it gets to the cyl's only cools the incoming air a bit. It doesn't cool the EXHAUST at all. Whereas, droplets which are turned to steam IN the cylinder are absorbing COMBUSTION heat, i.e. cooling the EXHAUST gases....i.e. "EGT's"
For best results, go for droplets instead of mist, and "linearize" the system, instead of just having "full/none".
I.e., put 3 small-capacity nozzles in the intake, and 3 microswitches on the go-lever. First nozzle comes on just off of idle....2nd nozzle at just below wherever your normal 'cruise' pedal position is; and the 3rd comes on somewhere near full pedal.
If your truck idles a lot, it'd be worth having the first nozzle on at idle; i.e. whenever the engine is running. (oil-pressure switch). The water-injection definitely helps prevent carbon-deposits; and removes deposits you already have.
Cruise flow should not be higher than 2gph for a truck that runs cruise-mpg of 10. Proportion the numbers to fit your own engine/mpg/truck etc..
I would strongly suggest injecting the water AFTER the turbo, btw.... Injecting prior to turbo will erode the compressor blades, and the blades also smash the water to mist; which will, again, prevent you from getting the EGT-cooling and MPG-improving benefits.
One of the Scandinavian truck-makers....Saab-Scania, or Volvo, did a big study of water-injection a few years ago. The report, or at least an abstract of it, is floating around the web somewhere. If you have access to SAE papers (big-city library, if you don't have an on-line SAE account), that same truck-maker published detailed SAE papers on it.
Actually, water-inj has been around forever. Most any decent ICE engineering textbook or handbook will have a chapter on it with the basics. The on-line archive of NACA (father to NASA) papers from the 1920's-1950's contains several papers on water-injection.
Keep us posted on results Mark! It's a good addition to a diesel...especially as fuel price continues to climb...