1998 Grand Caravan 3.8 AWD. 157,000 Miles. Have owned since new. Here's the problem. From time to time when I turn off the car, I hear a gurgling noise and when I look under the hood I notice that the coolant in the expansion tank is bubbling. I don't think it's boiling, but pressure appears to be coming from the radiator, through the hose, into the tank. Temperature guage reads normal. I pressure tested the system and there are no leaks. Replaced the cap just for the heck of it. No change. Happens about every 10 days or so. Any Ideas what might be happening? Thanks!

 

did you pressure test the cap?

 

Have you tried a thermostat. It maybe starting to fail. Stuck close at times.