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My 2012 Chrysler 300 is overheating. It bubbles when parked. The overflow reservoir was empty 4 days ago so fluid was replaced car was fine -- no evidence of leakage now. Reservoir is very low and car is overheating again. I think it's the cap, but could I be wrong? Is there anything else that could be an issue from what I've stated so far?

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    Welcome to the site. If you tell us what engine is in the car, you may get a more specific answer. – CharlieRB Jun 8 '17 at 18:34
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Overheating can be caused by a few things:

  • Coolant isn't circulating - pump, thermostat or other blockage
  • Insufficient coolant. Leaks, getting burned or air pockets.
  • System isn't holding pressure (cap or a leak)
  • Fans not working correctly. (Easiest to check)

Some possibilities are:

  1. Radiator cap, as you mentioned, which keeps the system from being properly pressurized.

  2. Fan isn't running. This doesn't have much of an effect other than when going very slow or parked. Could be a bad temp sensor, wiring to the fan or the fan motor. Fans rarely fail, but temp sensors are a maintenance item.

  3. Leaks. Radiator, overflow tank, hoses, etc.

  4. Water pump and/or thermostat. These will cause coolant not to circulate correctly. So, it just sits in place in the engine and gets hot.

  5. Head gasket(s). Coolant can leak into the cylinder and get vaporized, leaving you with insufficient coolant. The car may or may not run rough if this happens, depending on the severity of the breach in the gasket. You'd typically see white smoke (steam) coming out of the tail pipe, but it could be too faint to notice if the leak isn't large.

  6. Air pocket in the system, as a result of a leak or coolant system service. If no one recently touched the engine, this is unlikely unless one of the other issues mentioned above is present.

I'd start by pressure-testing the system. Some autoparts stores (O'Reilly comes to mind) will "loan" you a kit to do this. (Loan means you put down a deposit equal to the purchase price, and they'll refund it when you bring it back.) It's basically a bicycle pump with a pressure gauge, adapter for your radiator or reservoir. You pressurize the system and look for leaks: either visible leakage, or a drop in pressure on the gauge.

If that doesn't show a leak, do a compression test, or test the coolant for exhaust gaskets. Those would reveal a problem with the head gasket.

In any case, don't drive the car when it's overheating. These problems can get a LOT worse, very fast. If it gets hot enough, you'll be replacing the entire engine. If coolant is making its way into the oil pan (bad head gasket), the engine can seize since coolant doesn't lubricate very well. Too much heat can warp the heads and/or engine block.

Good luck!

  • Nice detailed answer. I agree with starting with the pressure test. Could be as easy as a bad cap. – CharlieRB Jun 8 '17 at 18:39

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