2002 Concorde 3.5 overheat
 

just purchased a 2002 Concorde that had, according to the owner, started to overheat but never got to red line and then was parked for seven months. She had taken it to a shop and was told she needed a water pump but could not afford to have it done. I bought the car, and had the water pump, timing belt, thermostat, flushed and refilled the system with new anti freeze, changed oil and filter, and serviced the transmission.

The shop owner drove the car after the work and said it started to overheat again. At this point, he drilled a 1/16th hole in the new thermostat base, and the overheat issue went away. He said that the overheat was the result of a passage between the block and head becoming clogged and the small amount of bypass the hole in the thermostat allows the engine to come up to operating temperature without over heating. I have since driven the car several hundred miles around town and on the highway and it has not shown any sign of overheat, but, it does turn on the check engine light each time and throws three codes, all of which indicate bad O2 sensors, bank 1 and 2, sensor 1 and bank 2 sensor 2. The shop owner says this because the bypass in the thermostat does not let the exhaust temp come up to operating temperature fast enough to satisfy the ECM. The car runs very well and pulls hard at highway speeds, and only occasionally has a short lived idle issue where it dies.






Does any of this sound logical to any other Chrysler fans?

First, I bet the thermostat is installed backwards, temp sensing element needs to face the block.
Second, bet someone replaced the o2 sensors with Bosch or other aftermarket.


If slow warm up was causing an issue it would set another code. (P0128)

Only O2 sensors you can use in a Chrysler are OEM or NTK

id agree with teh thermostat issue IF it only started to over heat after the new thermostat was replaced. In this cause same issue after the repair and before the repair. SO what he did was make the coolant loop all the time instead of doings its job and keeping the temp above 195. Being a 3.5 and only over heats when driven for awhile im gonna bank on the heads being warped and the head gaskets cant hold back the pressure and pushes out the coolant. the same results can be created by keeping the cooling fan on all the time the engine temp will never reach that 210 plus and wont over heat then.

Thank you both for your reply. I hate to think about the heads being warped. Is there a good and simple way to check for this? Since these posts, I have driven the car about 200 miles at "enthusiastic" highway speed and there was no coolant loss. Also, I see no signs of leaks externally. I really appreciate your inputs.

Does it overheat or run hot? Usually just below the middle of the gauge is normal.
Heads rarely warp on these engines. Only if severely overheated have I seen one case of this.
Fans work correctly?
Search at www.300mclub.org for a lots of good factual information

3.5 Overheat
 

Actually the car does not overheat at all now. It runs just under the mid point on the the gauge. Outside of turning on the check engine light, it performs flawlessly. It shows the following generic codes relating to the O2 sensors (I don't have the Chrysler specific codes) P0132 (Bank 1, sensor 1) P0152 (Bank 2 Sensor 1) and P0161 (Bank 2, Sensor 2, Heater Circuit).
A trusted shop that worked on the car indicated that when they replaced the thermostat and drove the car, it ran hot, but did not overheat, so they drilled a 1/16" hole in the T-stat body to remedy the run hot. They say this is the reason for the check engine light now in that the sensors are not getting hot enough fast enough to satisfy the ECM.
Does any of this make sense?

Another guess is that the O2 sensors have been replaced with Bosch or some other brand.
Only OEM dealer or NTK sensors will work in our cars.
(Scannerdanner on youtube explains why)