Fuel is used as a cylinder coolant, as well as your propellant. Heat is what destroys an engine. To check the heat of your engine, do not rely on coolant temperatures, as it is waaaayyy too late. Rely instead on an aftermarket EGT sensor (exhaust gas temperature).
Too high of an EGT and you'll start breaking stuff. The pistons will get a hot spot. The hot spot will start igniting fuel instead of your spark plug. Your pistons will crack and/or melt a hole through them. You lose compression. You lose your engine. Or the motor will detonate so severely it'll wear the bearing surface down on the crank rod journal so much that the bearing will eventually spin in the bore and a spun bearing=no oiling. No oil to a bearing=a lot more friction than you'd like and your engine sends the rod out the side of the block if you keep driving it while it knocks.
I can say with utter certainty that this is what will happen if you tune wrong. I've been down that road and did the expensive learning curve thing already a few times.
Don't rely on a dyno to tune your vehicle. Air flows much different on the street. Use a dyno for a base tune, or for information. But always always always fine tune on the street under real driving conditions. Some dynos do not put enough load on the drivetrain, resulting in unfavorably lean (albiet powerful) street conditions. Fun for a few miles, not so much fun after that.