I have recently read online that HHO kit helps to improve MPG by 20% -50%. ebay.co.uk/itm/HHO-Display-K … 4d0cf43288
youtube.com/watch?v=Xfk75WWtrFM
Is that true or it just sounds too good to be true?
If it sounds too good to be true…it usually is 
Hydrogen systems do have the potential to save fuel, but and this is a huge but, they will mostly be saving fuel as they’re replacing fuel with something else, so obviously they will require less petrol or diesel for a given amount of miles, however unless the thing replacing diesel has a higher rate of BTUs or is significantly cheaper then it will not be cost effective 
It could be like putting gold bars in the tank to save on diesel although the way fuel prices are going it will soon be cheaper to fill your tank with gold bars 
yes they do save fuel. but are more effective with petrol engines than diesel.
due to the high octane level of hydrogen you can’t put quite as much in a diesel as a petrol, but it does work.
best to try it on a tired old motor, that’s how you’ll see what a difference it can make.
Google it.
There’s a helluva lot more bad said than good.
So this hydrogen oxide is injected/sucked into the engine in what state?
In its liquid state (water) or in its gaseous state (steam)
See hydrogen hydrogen oxygen is better known as H2O aint it?
Bking:
So this hydrogen oxide is injected/sucked into the engine in what state?In its liquid state (water) or in its gaseous state (steam)
See hydrogen hydrogen oxygen is better known as H2O aint it?
on the ebay page it says
The voltage causes the water to dis-associate one of the electrons that hold it together and thus you turn water into a gas called oxy-hydrogen (or browns gas, HHO etc.) that can be burnt by your engine alongside your normal fuel to increase the combustion and reduce your hydrocarbon usage?
so I’d guess it’s steam ! ( a well known flammable substance ) 
Snake Oil.
Sound like wounder oil you want to be more efficant uses nitros oxide helps burn the fuel better but get it wrong and melt your pistons
Don’t forget to add some fuel line magnets for even better fuel economy. Oh and those balls you put in the fuel tank that agitate the fuel giving it a higher octane rating.
We got this system on 1 off ar trucks (a black box at back of cab) he says not much improvement in mph if any but has noticed pulling power increase.the system is on trial but company are not impressed