Improving gas milage with fine mist of water


Some years ago I was told I’d get better milage on a misty or foggy day. Then I read about a fellow who installed amist system in his trunk to improve milage. . .Is this a valid method anymore since fuel injection replaced carborators?


Water injection was popular a couple of decades ago, I don’t know if it would be a practical modification to a fuel injectored engine without modifications:


yes very popular with leaded fuel,no longer.


Probably due to the higher compression ratios that were used with leaded fuel. I’ve never played with it.


While there is theoretically some benefit for some engines with fuel injection (because the reduction in combustion chamber temperatures will reduce the tendency for knock, allowing a bit more ignition timing advance), I doubrt it would be worth the trouble and expense. Plus, I would be worried about how to meter the water mist properly.


The idea behind water injection was to allow lower octane fuel to be used by cooling the intake charge and reducing combustion chamber temps. During WWII, most aircraft required high-octane fuels, like 106 octane and above, that were hard to refine. Once jets came, and they use cheap kerosene, most piston engines were abandoned.

Another benefit of water injection was the reduction in carbon build-up. But, it will not improve gas mileage, except to the point of having a well-tuned and maintained car. This reminds me of the Youtube video, where a guy was claiming that adding acetone to gasoline will improve gas mileage. But, he started with a common 4-cyl econobox getting 16 mpg, and ended with the car getting 34 mpg. All he did was clean out the crap that caused a car that was built to get 34 mpg to only get 16 mpg from neglect.

To get optimal fuel mileage, keep your car in tune. If you’ve neglected the maintenance, or used crappy fuel at a lower octane than recommended, you may need a fuel system cleaning to remve the gunk an varnish that mat be reducing your mileage.


You should also consider the fact that water, and anti-freeze, is very corrosive to aluminum when it’s introduced into the combustion chamber.

Water injection, as used on some performance cars and some WWII aircraft, is only meant to be used sparingly and in wide open throttle situations.


OK4450 is absolutely correct about the corrosiveness with long term water use, and that it’s meant to be used sparingly.

The WWII aircraft primarily used it only during takeoff. They would overload the aircraft with bombs and then needed the extra power during takeoff. The water was used for extra power to help the plane get up in the air. Once up, the water was stopped.

When water is injected into a hot cylinder, it turns to a vapor, which is 16 times larger than the size of the original water droplets, which provides the additional push on the piston.

Water injection does pose some secondary effects, like a cooling in combustion chamber temps (as NYBo noted). I too would be worried about how to meter the water properly.


A race car performance calculator (that I found at some engineering University during my UGrad degree) had a surprising result to me. It showed that if the outside air had a higher humidity, you would get a better performance. That was in the early 90’s and a DOS program (probably won’t run if I could even find it). So in theory, engineers believe that increasing humidity increases engine performance.


Back in the '60s, the Olds F-85 Jetfire had a turbocharged engine that utilized a water injection system. As ok4450 said, this type of system was used only on full-throttle acceleration, and it was used for knock prevention–not for improved fuel economy. And, as was also said, while this was something that could be used on the carbureted engines of yesteryear, I have never heard of this being used on modern computer-controlled, fuel-injected engines.

Try to concentrate on keeping your car well maintained, drive it very conservatively, combine several short trips into one longer drive, keep the tires inflated properly, don’t use drive-ups windows at banks and fast food joints, and take excess junk out of your trunk if you want to get the maximum fuel mileage that the car is capable of.

I have recently found that I could easily improve my gas mileage by about 1.75 mpg just by accelerating much more slowly from traffic lights. I still drive at high speed, and I still accelerate briskly in order to reach highway speeds, but in more localized driving, I simply accelerate much more slowly–and so, without paying for equipment or additives sold by internet charlatans I have been able to make a difference in my gas mileage.


Slightly better mileage. The ideal ratio was about 60% water to fuel. Aside all the other problems with water, carrying 20 gallons of water with you has mileage costs. Big advantage was engines over 13 compression ratios.


There are some good answers here and some are contradictory.

Generally speaking better performance using the same amount of fuel will equal better mileage.

Water injection systems are used to decrease ignition knock and increase performance of gasoline engines using lower then recommended gasoline octane ratings.

Water has the side effect of “steam cleaning” the cylinders. You can pour water into the air intake while an engine is running to steam clean the cylinders and I often used to when getting a car ready to sell back when I was wheeling and dealing cars. In an old car this can dramatically improve how well it runs and it can even clean gummed up plugs.

Since water injection can help performance it will also increase mileage. As some have mentioned that improvement in mileage comes with a reduction in component life.

In other words long term exposure to water causes corrosion and early part failure which is why it should be used as little as is necessary.

In other words, yes, water injection improves mileage at the expense of damage to your engine.

Water injection should only be used if you plan on ripping apart your engine once every year or two to rebuild it the way the military and hot rodders will.



But, if added internally, it might damage hot engine parts.
See other topics, about Spark Plugs, etc. by me.