Description
My 2001 Volkswagen bug, always has the coolant light on, and when I open the hood, I can see the coolant boiling! Is it the thermostat??

Explanation & Answer

Never drive a vehicle with any sort of coolant leak.
The water is pressurized, so you can easily loose it all in seconds, and totally blow the engine in minutes.
Whether you did blow it or not is what you need to determine now.
A cooling system pressure test is best.
You replace the reservoir cap with a pump and gauge rented or borrowed from Autozone.
It should old pumped up pressure for 5 minutes.
When you start it, it should not oscillate when you rev the engine.
Also check for oil in the water, and water in the oil, making it look like chocolate milk.
You can also do a compression test.
You may have blown the head gasket, about $400.
Thermostats always need replacement after any over heating.
http://townhall-talk.edmunds.com/direct/view/.eea6dd4/1094
