My 97 camaro rs 3.8l i had a leak in the radiator it barley leaks its not to much of a big deal but i was driving today and the battery gauge went down into the red but everything was still working fine i then heard a knock and it just died and would not start back up seems like a dead battery but its got 12.45v at the battery and my alternator is good took it and got it tested and tested good. when i start the car it knocks only when i put it in gear and try to drive away but then it just dies and it wont start like a dead battery again then about 30 minutes it will start and everything all over again?

 

Where does the volt gauge sit, if you let it idle?

 

Is it auto or manual tranny? Have heard some torque converters cause knocking problems when they were going bad but not causing the motor not to start.

 

the gauge sits at about 14v but after about 20 minutes of driving it goes into the red and dies then you have to wait 20 more minutes for it to start back up at first it seems like the battery is dead but its not the alternator is doing its job but idk its automatic but it doesnt sound like a tourque converter

 

Sounds like your alternator. And yes some times a alternator will work when cold but as it heats up they will start to drop voltage. Also any leak in the radiator is a bad leak. You are lossing presure in the radiator which is used to keep the coolent in check. Each PSI lost in your radiator is the same as lowering your bowling point by few degrees. (For give my speeling)

 

Where does the knock sound like it is coming from? With your voltages reading what you say, sounds like the internal voltage reg on the alt is beginning to go.