Bad electrolyte. Wet cells always run hot. Keep trying.
Potasium hydroxide (KOH) or Sodium hydroxide (NaOH). Also known as potash and lye.
I was going to say most anything other than baking soda, but then I might come across as a knob.
Abo,
There is more information in this forum than any one of us can tell you. Some of it though is very basic, like what electroytes are the best. I read nearly every word of every thread and built several units before I ever made my first post. I may have gone overboard with it, but I wanted to have the fundamentals down before I jumped in with these guys that know so much more than I do.
If it helps you, there is a guy named Patrick Kelley that has a website that will really get you rolling. He even tells about a guy that reports to run his motorcycle off just HHO like you want to do. His website is a great place to start. I'm supposed to be getting someone else the URL, I'll post it here too when I find it.
Keep reading Abo and ask anything you don't understand.
I run a wet cell, and it runs pretty decently and doesn't get too hot, although it is winter. BUT this is only until I can rebuild my dry cell. They are the way to go.
1995 Chevy Camaro
17 MPG base city/highway
Listening to Van Halen
One issue we have is that there is no agreed upon temperature that is considered "too hot". In my mind, and it has been stated by others before, anything over 100 degrees is hot. That is where steam begins to be significant. Some people like some steam, I try not to make any.
So to clarify my position, I've not seen a bath cell that will stay below 100 degrees. If you have one, I will stand corrected (it wouldn't be the first time).