Engine Heating, Coolant Leaking!

I have a 2000 LS with 74k, I got it 7 weeks ago and drove it more than a thousand miles to bring it home. The drive was smooth and there was no problem at all. Two weeks ago, i was driving and the temperature just suddenly went up to Max and i had to park on the side of the freeway. I checked the coolant and there was none in there. I got some coolant and filled it up. The engine temperature went down and for next two weeks the engine temperature remained normal. Yesterday, i decided to check the coolant level and noticed it was a bit low. So, i added what was left from the previous container i got. I drove about 10 miles and parked, a half an hour later i got back into the car and in less than 5 minutes of driving, the engine started making a loud noise (which i suspect could be the fan) and the engine temperature rose up with the noise. I checked the coolant again and it was very low and was boiling in it. I also noticed it was leaking right below its container. I put more coolant in and as i was driving off, i could see the coolant leaking on the road in the rear view mirror. I stopped and checked, the coolant was once again low but this time, the engine temperature was normal so i drove the car home and planned to have my mechanic check it today. This morning it took me an hour and a half to drive 8 miles to my mechanic. The temperature was rising up again and when i put in the coolant, it leaks back out and i kept on stopping on the road to let the engine cool so i can drive another 30 seconds. When i finally got to my mechanic, he told me the engine is basically overheating probably because of the thermostat, the water pump or the fan. Now my question is, what is causing the coolant to leak? How is it leaking? Is the the coolant container also messed up or is there a way for the coolant to escape due to the other causes? Please advise me on this and what are possibilities in this case. If you have any questions please let me know. I thank you all for taking your time to read this.

I have a 2000 LS with 74k, I got it 7 weeks ago and drove it more than a thousand miles to bring it home. The drive was smooth and there was no problem at all. Two weeks ago, i was driving and the temperature just suddenly went up to Max and i had to park on the side of the freeway. I checked the coolant and there was none in there. I got some coolant and filled it up. The engine temperature went down and for next two weeks the engine temperature remained normal. Yesterday, i decided to check the coolant level and noticed it was a bit low. So, i added what was left from the previous container i got. I drove about 10 miles and parked, a half an hour later i got back into the car and in less than 5 minutes of driving, the engine started making a loud noise (which i suspect could be the fan) and the engine temperature rose up with the noise. I checked the coolant again and it was very low and was boiling in it. I also noticed it was leaking right below its container. I put more coolant in and as i was driving off, i could see the coolant leaking on the road in the rear view mirror. I stopped and checked, the coolant was once again low but this time, the engine temperature was normal so i drove the car home and planned to have my mechanic check it today. This morning it took me an hour and a half to drive 8 miles to my mechanic. The temperature was rising up again and when i put in the coolant, it leaks back out and i kept on stopping on the road to let the engine cool so i can drive another 30 seconds. When i finally got to my mechanic, he told me the engine is basically overheating probably because of the thermostat, the water pump or the fan. Now my question is, what is causing the coolant to leak? How is it leaking? Is the the coolant container also messed up or is there a way for the coolant to escape due to the other causes? Please advise me on this and what are possibilities in this case. If you have any questions please let me know. I thank you all for taking your time to read this.

You need to find if and where the leak is before changing thermostat or fan. It could be something as simple as a radiator cap that does not hold pressure. Does the fan come on at high speed when the AC is turned on? If it doesn't then the fan and/or its hydraulic pump is probably bad. Ask if your mechanic did a test to see if your cooling system holds pressure to check for a leak. As I recall there is a short bypass hose on the top of the engine that is prone to fail on these cars. I would check that first. I would check all hoses on the car.

Have you figured out your overheating problem? if so I would love to find out what the problem was. I am having a similar problem with my 2000 ls8. I have replaced the coolant resovoir, the termostat, the termostat housing, the water outlet pipe. Now I am looking at the water pump. I have had this problem ever since I replaced my mufflers.

Yeah my mechanic figured that the damn coolant reservoir was letting the coolant out for no reason. It lets the coolant out when it comes back from the engine but when the engine is off and you put in coolant, it doesn't let it out. He replaced the coolant reservoir and the problem is fixed. Final cost $210.