I have a 2004 Jeep Grand Cherokee SE. It has 191,000 miles on it. I bought the car a couple weeks ago and when I got home I realized there was no coolant in it. So I just put ZEREX 50/50 in the reservoir. Well a few days later i realized sitting still idling , the temp would rise above 210. So I checked the coolant and there was zero coolant in the reservoir once again! I have noticed a puddle of fluid under the car which I'm guessing is coolant almost directly under the reservoir. But I am not very good with engines so I really don't know what I'm looking for. Please HELP!

 

You need something called a radiator pressure tester. Autozone or similar store will loan it to you. Put it on the radiator where the cap goes and pump it up, it has a guage shows the pressure, and the leak should start leaking, allowing you to pinpoint it.

 

There have been occasions where the reservoir has cracked. Check it out. The junkyard is full of them for replacements.

Be careful what you put in it. Your 2004 doesn't take the green stuff anymore.