I can tell you that I worked for a Dodge dealer for the last 25 years and we had some head gasket problems with the 3.5 Intrepids now and then. Not alot but a few I could not forget about because they never showed up as a head or gasket problem. But I can tell you the car would usually come in with the overflow (burb) tanks partly melted. And many times you could let it sit and idle and after a bit the fans would come on but they would not bring the temp back down cool enough to turn the fans back off unless you drove down the road. One of the techs had this car an after a rad and thermostat and everything else we tested looked good he decided to pull the heads and they were warped enough that we had to replace them with new head gaskets. But we could not detect any combustion in the anti-freeze with our tester or see any air bubbles with air in the cylinders. We had a few more over the last 8 years or so that ended up needing the same thing. The funny thing was this tech and I always like to diagnose the problem the best we could and know what we thought was wrong before pulling anything apart but the first one we had we ended up pulling the heads not sure if we would find the problem since everything seemed to test ok. Good luck with it. Ron