Overheating

Tiny
WARFEK
  • MEMBER
  • 1999 CHRYSLER TOWN AND COUNTRY
  • 3.8L
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 200,000 MILES
My van started to overheat after idling for awhile. I changed the thermostat and that did not help the fans are working, but I have to run the heater on high to help cool the engine. It normally runs right below half on the gauge when the gauge hits the half mark the fans would come on and cool it back down. I finally had to unplug the coolant sensor and let the fans run all the time to keep it normal. I then changed the coolant sensor and plugged it back up. It idled at normal temperature then went to half mark and the fans turned on. I thought that fixed it but when I started driving on the highway it started to climb in temperature again. I pulled over and checked the fans they were both working. Does the fans have two speeds. After I changed the sensor and the fans came on for awhile they speed up turning a lot faster. I thought great it must be fixed. Why am I having to unplug the sensor and make the fans run all the time to cool the engine? I am at my wits end.
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Tuesday, June 13th, 2017 AT 7:36 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
The first thing to check is the cooling fins on the radiator. If they are badly corroded and crumble when touched, they will not be able to give up the heat to the air. The clue is the overheating stops when you run the heater fan on the higher speeds.

While it is not common for this engine, consider having your mechanic perform a chemical test at the radiator to look for a leaking cylinder head gasket. If combustion gases get into the cooling system, they will pool under the thermostat and prevent it from opening. Thermostats have to be hit with hot liquid to open. Hot air will not do it.
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Tuesday, June 13th, 2017 AT 7:54 PM
Tiny
WARFEK
  • MEMBER
Radiator is only a few years old still looks good.
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Tuesday, June 13th, 2017 AT 8:03 PM
Tiny
WARFEK
  • MEMBER
The coolant looked good but I flushed the radiator and put in new coolant. It still looks good.
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Tuesday, June 13th, 2017 AT 8:08 PM
Tiny
WARFEK
  • MEMBER
I removed the thermostat this morning and tried running it without it. That did not fix the problem so I unplugged the cooling sensor to make the fans run all the time. That keep the engine at normal temperature right below the half mark so I went and bought a new coolant sensor and replaced it tonight and hooked it back up. When the temperature went to half mark the fans kicked on. I wanted to see if they would cycle back off but a storm came through and I had to quit for the night. One thing that I noticed was after the fans came on and ran for about ten minutes they all of a sudden kicked on faster and were blowing harder. Is that normal to have a second speed. I had to turn it off because of the storm so I did not find out if the fans would cycle back off. Later on I headed home and had not drove for ten minutes when it moved up to three fourths on the gauge so I pulled over and checked it the fans were running but it was not cooling down. I let the engine cool and unplugged the sensor again. Started up and drove home the gauge stayed below half mark on normal temperature the rest of the way home.
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Tuesday, June 13th, 2017 AT 8:21 PM
Tiny
CARADIODOC
  • EXPERT
There were two versions of fan controls. One used a low-speed relay and a high-speed relay. Sounds like that is what you have. The other one used an electronic variable-speed relay. Those had some problems with shorted modules, then the fan would either never turn on or would run all the time.

What you need to observe now is if the overheating occurs while driving at highway speeds. If it does, the fan is not the issue because it is not needed at higher speeds when natural air flow is sufficient. Then I would be looking at a leaking head gasket.
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Tuesday, June 13th, 2017 AT 9:00 PM

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