I recently had my thermostat replaced due to hearing bubbling in my coolant tank once I turn the car off I also noticed on the opposite side other coolant tank there was leaking on the ground not a lot but it was I thought maybe it was oil cuz it was over there by the oil side but I'm not too sure about that but it was fluid. I had no problems for about a week. I noticed as I park my vehicle I once again heard the bubbling sound as I begin my destination from the grocery store I drove home and kept my eye on the temperature gauge which went halfway and continue to stay a half way until I got home which was 30 to 45 minutes later once I was got home once again I hear the bubbling sound. Any suggestions? ???
Bubbling like this can be caused by a leak in the cylinder head gasket from one of the cylinders to the water jacket. Since your water temperature is normal it is clearly not an overheating problem. It is possible for a garage to use there exhaust gas analyser to sniff the coolant reservoir for exhaust gasses to diagnose the problem.