[lowsonoma1999]

serge, he added fuel injector cleaner to help fix his problem, it was not the cause. Plus, in all my years in the automotive industry, this is the first time I have heard anybody accuse injector cleaner as causing bad head gaskets and piston rings.

brown, more than likely it's something electrical. It sounds like something is shutting down when it gets hot, and then when it cools off, it starts working again. Used to be a problem with Ford Taurus' all the time. I have seen it a couple times on Hyundai's, but not very often. It has been awhile, and I can't remember what the cause was. Could be possibly a coil, or something else with the ignition. To narrow it down, you are going to have to figure out if it's a lack of fuel or lack of spark when it won't start.