Q: My Lincoln is still overheating, why?

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I've put a ton of money under the hood of my car trying to get rid of this problem if you're going to say something generic don't bother. I have changed all the plastics in the cooling system: thermostat housing and everything connected. It has a new degas bottle and hydraulic fan motor, shroud, and blade. I need an EXPERT to help me know what to do next. Temp sensor? Hydraulic actuator? Computer? Something I don't know about? Help me???!!! Thank you

My car has 201000 miles.
My car has an automatic transmission.

A: First off, I won't be able to tell you ...

First off, I won't be able to tell you what is wrong with your car. I can only give you a guide to figure it out. There is way too much information to explain all the possibilities here. Before you do anything more, make sure the cooling system is full. With all the parts you have replaced I must assume it is full without any leaks.

Next, is this really overheating or is the gauge just reading wrong? The best way to determine this is with an infrared temperature gun. An infrared gun is the only way to know for absolute sure. Once you have an infrared gun, you want to take measurements at the thermostat housing and several other locations. The highest temperature that is safe is around 225 degrees Fahrenheit. If your car is not overheating, but the gauge says it is, a good place to begin is by replacing the engine coolant temperature (ECT) sensor.

The ECT temperature should be checked with a scan tool to see if it correlates with the temperatures you are measuring under the hood. Keep in mind, you have the sensor, PCM and instrument cluster involved with this reading. While it is rare for a PCM to fail, instrument cluster failure is fairly common, but the sensor itself is the most common.

In my research to find the location of the ECT, I discovered your car uses a CHT (cylinder head temperature) sensor. This makes the need of a scanner to monitor data that much more important because the PCM is using the CHT data to calculate the coolant temperature sensor. If I were working on your car, I would be looking for confirmation of this since this is not a common method to determine coolant temperature.

If the data all agrees and your car is overheating, then you can begin to figure out why it is overheating. Begin with a cold motor and warm it up until the thermostat opens. You will know the stat has opened when the upper radiator hose gets warm and then hot. You may need to run the car at a high idle for sometime to reach this point. Every car is different. I would be monitoring coolant temperature on a scanner and with a temperature gun with your car. If the thermostat opens and the car doesn't overheat, its time to move on to the next possibility.

Is the radiator clogged, or is the water pump not pumping coolant? For this, I would begin by testing the water pump by removing a coolant hose with the motor off. You will need to determine which hose to remove. It should be one that will have good coolant flow. Again, this takes some understanding of how the coolant flows through your system. I cannot make this determination without being there. With one end of a coolant hose removed, start the car and see if coolant flows out the hose. Sometimes you may need to rev the motor a little. But not very much. This test can often be inconclusive, so keep this in mind. If it doesn't move at all, then there is likely a flow problem.

Next is the radiator. To test it, make sure the thermostat is open, drive the car around the block and come to a stop, turn the motor off, lift the hood and reach in a touch the radiator from top to bottom and side to side. It is normal for the bottom of the radiator to be cooler than the top. But you don't want to find random cold spots. If you do, your radiator is clogged and it will need to be replaced.

Finally, there's the possibility of a head gasket issue. The best way to check for a head gasket failure is with a hydrocarbon (HC) detector. Most people don't have access to one, so the next best thing is to rent or buy a block tester from your local auto parts store and follow the instructions.

This is the best I can do in this context without actually seeing the car. If you don't have any luck with this, or you need some extra help, an expert from YourMechanic can come to your car's location to diagnose the overheating problem in person to determine what fixes are required.

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