Hyundai Repair: 2006 Hyundai Azera V6, coolant temperature sensor, 2006 hyundai azera

Question
My car does not actually get hot, but when it is really hot outside and I use the air conditioning on hi my temp gauge will creep up to hot in the red and slowly creep down and back up again and stay for awhile in red, but if I keep the air on low it will stay at normal on the gauge. Several mechanics and wiring people have looked at it and have no idea why it is doing this. A new temp switch and thermostat was put in and still continues. It only does it when the outside temp shows 98 on up degrees. Do you have any ideas what is causing this? Once a gain the car itself does not get hot. Thank you for your input.

Answer
Hi, Mary.  If you or your mechanic have determined that the coolant temperature is normal but the gauge shows the temperature is in the red zone, then you may be getting feedback through the coolant temperature sensor.  If your mechanic has a scan tool capable of reading the coolant temperature from the engine control module (ECM), he can then verify the actual coolant temperature as compared to what is indicated on the gauge.

What I've seen (although I've not seen it on an Azera as yet) is that when the air conditioning is on, there isn't sufficient ground path from the engine to the negative battery post.  The air conditioning compressor grounds to the engine block, which then relies on the ground strap and negative battery cable for the rest of the ground path.  To diagnose this issue, you'll want to take a voltmeter and clip one lead to the negative battery terminal while the other is on the engine somewhere.  Then turn on the engine and a/c.  The reading should be less than 0.1V (100mV).  If it's more than that, your ground path isn't sufficient.  Similarly, you can check from one end of the ground strap to the other and from the negative battery post to the body of the car to find whether the excessive voltage drop is in the strap or cable.  I have seen some Azeras where the contact between the negative cable and the body of the car was poor, but this typically resulted in the engine not starting intermittently.