I have a 99' SLS, V8, 4.6 northstar engine with a 102K on it. Everything has been fine since I bought it (6 months ago) but now it is sucking down the coolant. I have had to replace the coolant three times in about 2 months. The engine still has power, sounds fine and does not overheat so I am puzzled. I do not know what is happening. I would be very greatful for any help/advice with this situation.