I have an 02 beetle that is losing coolant. No drops on the ground, can't find any wet spot and not overheating. I did try to do a pressure test and found that as soon as I build any pressure at all it leaks out the bypass on the overflow ball. I can't get it to 2 pounds before it leaks down. is that normal or should I be able to pressurize it? If so does anyone what pressure it should run at ? I'm guessing 18-20 but not sure.