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her209
03-28-2009, 12:48 AM
Symptoms:

- there are two fans: radiator and A/C
- when A/C off, radiator fan does not turn on automatically
- when A/C is turned on, both fans turn on and off at the same time automatically
- engine temperature gauge shows close to overheating (assumed to be correct as temperature gauge appears working when car is warming up)
- turning on A/C appears to bring down the temperature shown on the temperature gauge

Troubleshooting Steps Performed:

- radiator coolant was flushed and refilled
- checked relay fuses to radiator and A/C fan
- unplugged the temperature gauge connector (next to coolant temperature sensor) in engine bay. Gauge on dashboard unresponsive.
- unplugged the coolant temperature sensor in engine bay. "Check Engine" light on dashboard comes on.
- warmed up the car to normal temperature with radiator cap off to see if radiator fluid was circulating. Inconclusive due to car shakiness.
- gauged temperature of top and bottom radiator hoses by hand. Both seemed to be equally hot, although, turning on A/C seemed to make bottom hose slightly cooler

Possibly Relevant Info:

Car is a 1994 Toyota Camry 4-cyl.

Question:

Which could it be: thermostat, coolant temperature sensor, or other?

EDIT: Added more troubleshooting steps performed.

Aimster
03-28-2009, 01:05 AM
I thought it turned on when the engine was warm?

her209
03-28-2009, 01:27 AM
Originally posted by: Aimster
I thought it turned on when the engine was warm?
Its supposed to (and did). Now it doesn't.

LTC8K6
03-28-2009, 01:45 AM
Unplug the coolant temperature sensor while the engine is running. This should cause the fans to turn on low then kick to high, IIRC.

Typically when the engine computer loses the signal from the coolant temp sensor, it just turns both fans on high so the engine will not overheat.

LTC8K6
03-28-2009, 01:50 AM
IIRC if you ground the gauge wire, the gauge should go to full scale.

her209
03-28-2009, 02:00 AM
Originally posted by: LTC8K6
Unplug the coolant temperature sensor while the engine is running. This should cause the fans to turn on low then kick to high, IIRC.

Typically when the engine computer loses the signal from the coolant temp sensor, it just turns both fans on high so the engine will not overheat.
In the troubleshooting step above, I unplugged the coolant temperature sensor and then ran the engine. Neither fan turned on (however, I don't think I waited long enough), i.e., I turned off the engine withing 10-15 seconds of starting it and I did not turn on the A/C. I will give your suggestion a try tomorrow.

her209
03-28-2009, 02:01 AM
Originally posted by: LTC8K6
IIRC if you ground the gauge wire, the gauge should go to full scale.
Do I just use an alligator clip and connect it to body of the car?

bruceb
03-28-2009, 08:47 AM
First when you did this step "unplugged the temperature gauge connector (next to coolant temperature sensor) in engine bay. Gauge on dashboard unresponsive" and the gauge did not respond, then that is most likely the Sensor to tell the Fan when to come ON .. Also they work by completing the ground path to the engine computer input, which in turn will turn the fan on. Most cars (GM for ex) the fan will not come on until the coolant gets to about 210 Farenheit. Other cars the cut in range may be lower. Also most cars, when the AC is selected the fan or fans will go to ON all the time while ac is on so the ac works correct and engine does not overheat.

Musclecar
03-28-2009, 07:05 PM
Have the very same issues w/my 1994 Camry 4 cylinder. Investigating now.
1) Replaced the thermostat - still over heats.
2) Flushed the radiator - still over heats.
3) There is a radiator coolant temperature sensor below the fan on the passenger side. Disconnect the wiring plug and both electric fans should start when the engine is started and run will continuously with the engine. If not, you have a fan or relay problem. In my case, the fans run, but the engine still overheats.
4) I noticed today that the upper & lower hoses are hot, but the radiator itself is cold.
I suspect the water pump or a plugged radiator. Stay tuned.

Gillbot
03-28-2009, 11:07 PM
Check the fan relays themselves, They can also go bad. I had this problem on an older Chevy. I just ended up wiring the fans to the ignition to get me by but forgot and never removed them.

LTC8K6
03-29-2009, 03:44 AM
Use whatever will work to ground the connector. A paperclip or a nail? Whatever will fit into the connector to allow you to touch it to a ground.

The gauge connector is typically a single wire, whereas the coolant temp sensor for the computer has more than one wire.

her209
03-29-2009, 11:15 AM
Originally posted by: LTC8K6
Unplug the coolant temperature sensor while the engine is running. This should cause the fans to turn on low then kick to high, IIRC.

Typically when the engine computer loses the signal from the coolant temp sensor, it just turns both fans on high so the engine will not overheat.
Sorry for not getting back to this thread sooner.

I disconnected the coolant temperature sensor while the engine was running and both fans did not turn on. There was another "sensor" located on the radiator referred to as "engine coolant temperature switch". When this is disconnected, both fans continuously run at high speed. I believe this is the source of the problem.

However, while looking around, I noticed that the car was leaking coolant. I am attempted to trace where the leak is occurring but I will most likely take it into the shop.