I don't know really, but what I've learned is to take off the rad cap(when cold, not hot, unless you want to be burnt). And then start the car, If it starts to bubble, like air bubbles, then you have a leak, then look under the car for any drippage, If there is some, look to where it's dripping from, then look up to where it's originataing from. It helps to generalize the area of the leak, then focus on that area, and look for any signs of a leak, Like buitl up white grungy s***. You may not have a leak, but it might just get so hot that the coolant vents out of the over flow canister, or it might burn off. I don't know how acurate this is, but the leak test is reasonably solid, I've used it in past cars, and in Auto shop often enough to know it helps.