Beetle Engine Problem

Hi, I have a 2000 VW Beetle 2.0L. It just turned 70K miles this week and due for a oil change and service. Today morning, I was driving the car, but for no apparent reason, the car started bipping, and then I noticed the high-temperature red light started flashing on and off. I poured some engine oil, water, and anti-freeze. Then after I let it cool down, I took it for a spin again. After driving for a while, same problem, and then I saw "check engine" lights turned on, and now it happens every time I start the car. The dealer/factory warranty is over, but I am still taking it to the local VW dealer next week. They said to tow it, even though the car runs fine, except those warning signs. What could be the malfunction? Any solutions? Thank you very much.

Is the coolant level low again?

I believe engine oil was low, perhaps there is a small leak somewhere. Maybe that's why engine overheated and threw water out?

Water leaks are fairly common, I'd think the level got low then the engine overheated. Engine oil would have to be very low to cause overheating, and you would have probably heard some bad noises too.