This is my first post to this forum so I hope I do it right. I really need a diagram of the coolong system showing all the hoses and connections.
I have a 2002 Concorde with the 3.5 liter engine that is boiling over even though the temp gauge never goes beyong the 3/4 mark.
I bought this car from a private dealer who I thought was giving me a good deal. What I found out later is that after it has been running for a while and is brought up to highway speeds, it starts to boil over (the test drives were to short and quick to discover this issue). I didn't have time to do anything but the simplest diagnosis so I brought it to mechanic. He tested everything and replaced the water pump, thermostat, radiator, coolant reservoir and cap and backflushed the heater core. These items were replaced one at a time after the previous "fix" didn't fix it. After all of this the problem remained. I then brought the car to the local Chrysler dealer to see what they could do. A $1000 later after another new water pump, timing belt, coolant reservoir cap and thermostat, the problem remained. They then did what they called a "clear hose test" which supposedly checks the coolant passages throughout the engine. They told me that the coolant passages in the block were plugged and a rebuild or new engine was required (probably due to the dealer adding something to stop leaks). So I bought myself a rebuilt long block and swapped the engine out. THE SAME PROBLEM REMAINS!! While I was putting the new engine in, it occurred to me that the routing of the coolant hoses on the original engine seemed odd. There is a four-way connection at the rear of the engine that connects the heater core, the coolant reservoir, the thermostat housing and the PCV valve together. Why would the PCV valve, which is attached directly to the rear of the upper intake manifold, have a connection to the cooling system?!?! I think what may be happening is that hot engine gases/exhaust are being pumped into the coolant and causing it to boil over. So $4000 of parts and repairs later and I am right back where I started.
Sorry for the long post but there has been a lot covered trying to resolve this problem and I am out of ideas.