My engine coolant light is always on. When it came on the first time I checked the coolant level and decided that it wouldn't hurt to add some, so I did. But the light stayed on. Sometimes it would turn off for a minute or so then come back on. I added the coolant about a week ago. I checked it earlier today and it was much lower than it was last week. The coolant I added clearly disappeared too quickly. What may be the problem?