Overheating in stop and go traffic.

Tiny
TYAZZ
  • MEMBER
  • 2000 DODGE DURANGO
  • 4.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
I use the vehicle for a mail route. The heat hasn't been working (Blow outside temperature air). It's been overheating during the stop and go, but not on straight drives. I've replaced the thermostat, clutch fan, and water pump. What next?
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Tuesday, April 21st, 2015 AT 2:52 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
Both of these symptoms can be caused by low coolant level but with the parts you replaced already, at some point the system should have been filled.

The next thing is to feel the hoses when the overheating occurs. If the upper radiator hose is cool, a leaking head gasket might be a suspect. Combustion gases can pool under the thermostat and prevent it from opening. Thermostats have to be hit with hot liquid to open. Hot air won't do it. If the hose is hot, feel the two heater hoses. They should be too hot to hold onto for very long. If they are cool, the heater core is likely plugged. Remove the hoses from the engine, then run water through them from a garden hose. I prefer to not remove them at the heater core because besides limited access, on some cars you run the risk of breaking the solder bond between the pipe and the heater core, then you have an expensive leak.

Do you get hot air inside at highway speed?
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Tuesday, April 21st, 2015 AT 3:35 PM
Tiny
TYAZZ
  • MEMBER
There is no heat at highway speed. The top radiator hose is hot. I bypassed the heater core already to eliminate that as a culprit. Just noticed that the bottom hose isnt hot but the thermostat housing that it runs into is. Could that mean anything?
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Tuesday, April 21st, 2015 AT 5:42 PM
Tiny
CARADIODOC
  • EXPERT
You won't have any hot air inside with the heater core bypassed.

If the upper radiator hose is hot near the radiator end, coolant is circulating. Feel across the radiator to see if there are some cold spots and some hot spots. If there are some of each, parts of the radiator are plugged. Normally that causes the engine to run hot at higher speeds, but sometimes the natural air flow at higher speeds brings the temperature down too. Also look for corroded cooling fins on the radiator. If they crumble when you touch them, it's time to replace the radiator.
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Tuesday, April 21st, 2015 AT 6:20 PM
Tiny
TYAZZ
  • MEMBER
The whole radiator felt cool, even though the top hose was hot. The sides of the radiator are hot but thats it.
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Tuesday, April 21st, 2015 AT 6:39 PM
Tiny
CARADIODOC
  • EXPERT
I think I'd start with a cooling system flush, then see if the entire top of the radiator is hot.
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Tuesday, April 21st, 2015 AT 6:49 PM

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