will my engine heat increase after installing this product?

It’s a surprise to us as well as HHO suppose to cool the engine as what the theory is on the internet but upon our experience it’s a slight insignificant increase due to the additional hydrogen gas added to your fuel.

Is there any possibility that the engine will damage while testing or installing the EFIE?

No, your engine will always be intact. Only if the EFIE is not installed properly will effect your ECU thats why I have to get my self a very good technician (wireman) to do it rather than any other wireman out there. There is infact "no risk" so far in our experience in installing both the EFIE and the HM80. risk is always there even though the percentage is very small. But if you ask me to define the risk I've seen none so far.

Does it harm the engine?

No it doesnt, In fact it helps to clean the engine and infact inproves
the performance as long as the device helps to filter out the steam and
electrolyte solution from the HHO gas