Q: My car runs hot but it never overtheats the temperature gauge moves up and down

This is could be a classic symptom of a cooling fan not operating. When your car is moving, air is passing over through the radiator allowing it to dissipate heat. When you car is at a stop, there isn’t any air flow passing through the radiator while stopped. That is where the cooling fan comes in. The symptom you describe with the temperature gauge could indicate other problems though.

If the temperature gauge is fluctuating while driving, this indicates there is a low coolant condition or the thermostat has problems. On a car with 125,000 miles, I would definitely suggest a new thermostat. But before you put one in, you should take a look at a few things first.

Check the coolant level cold. If the coolant is low, you need to find the source of the coolant leak. The 3.8l has a few common coolant leak failures.

• Water pump
  
• Upper intake plenum will leak into the cylinders.
  
• And the drive belt tensioner.
  
• Water pump bypass elbow.
  

The drive belt tensioner has coolant passages in it that feed the heater core. The pipes that come out of the tensioner are sealed with rubber o-rings.

The water pump bypass pipe is usually plastic. There are after market elbows that are metal.

Of course there are the usual suspects such as hoses and the radiator, but you will need to pressurize the system to find the source of the leak.

If you need some help with pinpointing the issue, consider enlisting a certified who can find find the coolant leak as necessary and diagnose the several other components I’ve mentioned above.

Good luck, and remember to change the thermostat even if you find a coolant leak.