Chrysler Mysterious Overheating

We all have war stories to tell about ‘those cars,’ right? Here is one that anyone who works on cars and works with the owners of those cars can relate to. The symptom on the 2004 Chrysler Concorde was the engine coolant temperature gauge was running hotter than normal. Since the customer was rather attentive, he wanted the shop to look into this concern because it didn’t seem normal to him.

After some preliminary inspections on the vehicle, such as coolant level and overall cooling system condition, it was determined that everything looked fine, including cooling fan operation. A check for combustion gases in the cooling system was performed to rule out a head or head gasket problem, and that was negative as well. The technician took the vehicle for a road test and found it ran perfectly, with no apparent problems with the gauge or the engine temperature, verified with a scan tool. According to the scan tool, the engine was running around 190 to 200 degrees; nothing that looked out of the ‘norm.’

We have all been in these positions before. What was the customer trying to say? In a busy shop environment, taking the time to get all the information from the owner is important. Sometimes they offer it and other times they do not. Like the old adage goes, maybe they think it will cost them more if they tell the repair shop everything. Thankfully, that is usually not the case — most often customers do not understand the complexity of repairing vehicles and may just assume it will be simple to diagnose and repair.

A second conversation ensued with the owner and more details began to unravel. The vehicle was purchased new. While it was under warranty with less than 10,000 miles on it, it ran hotter than normal on a long trip. According to the service records, the vehicle had its cooling system flushed and the radiator was replaced. Again, this was done under warranty. After those repairs were made, there were no further symptoms for several years.

Was this the same problem or something completely different? The vehicle now had around 85,000 miles on it. One would think this would be a different issue with all the time and mileage that had elapsed. After further discussions with the customer, a strange pattern started to emerge: There was no rhyme or reason when the temperature gauge would start indicating a hotter than normal running engine. The customer stated, “Sometimes it happens a few times a year, sometimes it shows hotter than normal on a 30-mile trip.” A few times per year? Really? Certainly, gathering this information helped to better understand why the customer was concerned. It seemed to be an ongoing problem with no consistencies.

The shop had done some research and found there were some problems with the thermostat on this engine, as well as a cooling system passage that gets restricted (Figure 1). After learning this, it was decided that the thermostat and its passage should be removed and inspected. Upon inspection, nothing unusual was noted and the cooling system passage was clear. Not much of this passage can be seen, but compressed air was blown into the passage just to make sure it was clear. (Figure 2), (Figure 3) A new thermostat was installed and the vehicle was put back together and tested again.

On the road test, the cooling system seemed to be operating at normal operating temperatures on the gauge as well as on the scan tool. Not feeling overconfident, the technician let the customer take the vehicle with the understanding that he would report back to the shop if it started to run hot again. Three weeks went by without hearing from him. Then late one afternoon, he stopped in to mention that “It did it again.”  This time he had more information; now it would run hot after 30 to 50 miles of driving.

Arrangements were made to have the car dropped off — this time for several days so it could be driven 30+ miles. After the longer road tests, the technician finally noticed what the customer was talking about. The temperature gauge was running at about the halfway to about the three-quarter point on the gauge (Figure 4). This was certainly much different than previous road tests. The actual scan tool temperatures were in the 230 to 250 degree range rather than under 200 degrees. A quick check under the hood — both cooling fans could be heard running at high speed. What seemed interesting was that the air blowing from the radiator was cold, especially on the driver’s side of the radiator. And the lower radiator hose was cold to the touch. Was this just a case of a plugged radiator again? Why were the radiators getting plugged? More investigation was needed at this point.

The next day, after thoroughly checking the cooling system flow diagram (Figure 5), the technician realized the coolant was not entering the engine, since the radiator and lower radiator hose were cold when this event happened. What about the radiator and the history of the radiator replacement several years ago? These were weighing on his mind. After more pondering, he temporarily removed the thermostat and ran the engine to see if the problem reoccurred. After a few days of driving a lot of miles, the engine ran cooler than normal, as one would expect without a thermostat in the engine. If the radiator was plugged or restricted in any way, it should still be running hotter than normal, but it wasn’t. That test confirmed that the water pump was circulating properly and the rest of the cooling system was in working order.

Was it a bad thermostat? It couldn’t be — this one was brand new. Was there still something in the passage keeping the thermostat from operating properly? Many questions, but not many answers yet!

Another new thermostat was ordered and the passage in the cylinder head was blown out thoroughly. Once again, there didn’t seem to be anything restricting this passage. The water pump impeller can be accessed with a long thin screwdriver while the thermostat housing is removed on this engine. The funny thing is, the impeller seemed to be able to move. That shouldn’t be; it should be tight. The water pump on this engine is driven by the timing belt. Was the impeller loose on the shaft of the water pump? Was the timing belt loose? By now the technician’s head was starting to hurt!

The new thermostat was installed and the vehicle was driven 30 to 40 miles with no problems. The vehicle was kept overnight and then a much longer drive was performed. All temperatures were now normal! Maybe it was just a bad thermostat.

The customer needed the vehicle back, so it was agreed he would drive the vehicle and report any further problems. A few months later, he stopped by for an oil change and said everything had been just fine; no overheating, and the temperature gauge was running normal. So it must have been the thermostat, the technician thought.

Several months went by and guess who stopped by? Yes, the same customer was back, and the car was running hot again. But this time the symptoms were different! Now, the temperature stayed relatively normal as long as the heater was on. If the heater was off or blended to cooler airflow, the engine would start running hot again. But it still had to be driven over 30 miles before this would happen. So to duplicate the problem, the vehicle had to be driven about 30 miles and the heater had to be off. Then it would start to run hotter than normal!

After road testing, it was discovered the customer was right. If the heater was on, it would actually bring the temperature back to a normal range. Once again the technician noticed the a
ir coming off the radiator with the cooling fans on high was cold, as was the lower radiator hose. Thoughts turned back to the water pump impeller and the timing belt. It didn’t make sense that it could be a water pump problem but this engine does have a plastic impeller. Maybe it was spinning on the shaft at times? The timing belt cover was removed. Before removing the timing belt, the technician tried to turn the water pump by hand and much to his surprise, he could turn the pump with the timing belt still in place. That would mean the timing belt was loose because of a bad tensioner, but the timing belt seemed tight. So the technician removed the timing belt, timing belt tensioner and the water pump, and then replaced each of them with new ones. The water pump had a little wear on the impeller but was tight on the shaft. He proceeded to put it back together and try it out again. After multiple 30+ mile road tests, the temperature seemed normal, even with the heater off. By now it was spring and getting warmer outside, not quite to the air conditioning season, but getting close. It must be fixed, the technician thought. Back to the customer it went.

About 500 miles later, the customer stopped by to say, “It started running warm again.” The technician was at a complete loss. And out of sheer frustration after looking at the cooling system flow, the decision was made to pull the driver’s side cylinder head to closer inspect the passage that goes to the thermostat, in hopes that something would show up there. After the head was removed, this is what was seen (Figure 6), (Figure 7), (Figure 8). It appeared to be metal shavings — nice curly Q’s severely restricting the passage to the thermostat. This has to be the problem; now things were making more sense. The passage was getting so restricted, the thermostat was closing off. On this engine, the thermostat is very dependent on this passage to help keep it open. That is why the radiator was cool and the lower hose was cold. The coolant was being cooled by the radiator, but this cooled charge of coolant was not going back into the engine because the thermostat was closing off due to this passage restriction.

The head was cleaned up a bit and a small amount of metal was removed to ‘open’ up this passage a bit (Figure 9). In case there were more shavings in the engine, this would provide a bigger opening to let them pass through. Clearly this had to have happened during the engine building process and was likely the problem, even while the vehicle was under warranty. Whenever the cooling system was drained or flushed, these shavings found a new home — until they became dislodged and made their way to the cylinder head, where they restricted the passage. It was very interesting that they lay dormant for so long, several years and many thousands of miles.

After cleaning out the debris and reassembling the engine, many road tests were made and the system was now normal. Just to be sure, the technician followed up with the customer every few weeks. What a war story! A few tips came out of this experience:

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Water pump impeller access can be accessed by removing the thermostat and using a long thin screwdriver to see if the impeller is loose on the shaft (Figure 10).

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Total system flow. By removing the thermostat, the water pump, radiator and other system flow problems can virtually be eliminated if the temperature seems cooler than normal.

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Draining and refilling the cooling system can cause the shavings or debris to ‘settle’ temporarily causing a false indication of a repaired cooling system.

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Cooling system passage. Just because you can blow into this passage with shop air, this really doesn’t confirm it is completely open. But it will determine if it is completely plugged.

After all the headaches and head scratching, here is where the gauge runs after the repairs (Figure 11). Note it is always on the underside of the halfway mark on this engine, when the cooling system is operating normally. This is true ‘normal’ for this engine. Many customers may not even notice this problem because, as seen in the previous figures, the engine is still running in the normal range according to the gauge. There is no warning to the driver because it never gets into the ‘red’ portion of the temperature gauge.

This mysterious overheating car just had a plan of its own. But thanks to a patient customer and a persistent, organized technician, this one was finally fixed.