Turn my car on it cranks stays on for about 30 seconds then turns off. My battery is fine all the lights in the car and on the dash stay on its just the car itself does not. Turn it back on give the gas a few pushes once it cranks amd it stays on just fine no issues. It does not cut off as im driving only when I first start it and its doing this on and off sometimes it cranks right up no issue other times it cuts off and I have to restart it. My dad said it was my radiator but it cant be because its full of coolant so please advise.