QuestionThe answer doesn't fit the problem. If the thermostat was not functioning and there were an air bubble in the system it would seem like the fan would come on all the time. My problem is that it is not coming on unless the a/c switch is turned on. I guess the easiest fix would be to run the fan all the time?
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Followup To
Question -
I have a 96 cavalier with 4 cyl, ac/auto trans. After the car has run a while the temp guage goes into normal range then slowly creeps into hot range but doesn't boil over. I found that the radiator fan does not come on when the engine is hot. If I turn the a/c on then the fan will run but stops when the a/c is turned off.
I changed the temp sensor thinking that was the problem but no luck. I also swapped the relays in the fuse block and that didn't make any difference. Any ideas on what I should look at next?
Whatever tells the fan to run is not doing what it is supposed to be doing. thanks for any info.
Answer -
Sorry for the late response.
Its either a bad thermostat or air pocket in the cooling system.
Swap in a new thermostat and bleed the antifreeze very well.
AnswerThe fan comes on when the coolant temperature reaches a certain level. Your problem isn't why the fan isn't coming on but rather why your car is overheating or coming close to overheating.
A bad thermostat can get stuck open or closed preventing proper cooling.
An air pocket in your cooling system can also create the same result. The ECT sensor will give an incorrect reading.
But if you haven't lost or changed the coolant recently, than its not an air pocket.
Not sure where it is on the 96 Cavaliers but here is the info on the last 99 Cavalier I worked on...
http://www.autozone.com/images/cds/jpg/small/0900823d80191d79.jpg
Fig. 1: The ECT sensor is located in the water outlet housing, adjacent to where the upper radiator hose connects to the engine
http://www.autozone.com/images/cds/jpg/small/0900823d80191d7a.jpg
Fig. 2: ECT sensor location-2.4L engine
http://www.autozone.com/images/cds/jpg/small/0900823d80191d7b.jpg
Fig. 3: ECT sensor location-1998-00 2.2L engine
The Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT also is used for temperature gauge operation by sending it's signal to the instrument cluster.
The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.
TESTING
See Figures 4, 5 and 6
http://www.autozone.com/images/cds/jpg/small/0900823d80191d7c.jpg
Fig. 4: Detach the connector on the ECT sensor
http://www.autozone.com/images/cds/jpg/small/0900823d80191d7d.jpg
Fig. 5: Measure the resistance across the ECT terminals on the sensor
http://www.autozone.com/images/cds/jpg/small/0900823d800e5643.jpg
Fig. 6: ECT sensor resistance value chart
Disconnect the engine wiring harness from the ECT sensor.
Connect an ohmmeter between the ECT sensor terminals.
With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
Connect the engine wiring harness to the sensor.
Start the engine and allow the engine to reach normal operating temperature.
Once the engine has reached normal operating temperature, turn the engine OFF.
Once again, disconnect the engine wiring harness from the ECT sensor.
Measure and note the ECT sensor resistance with the engine hot.
Compare the cold and hot ECT sensor resistance measurements with the accompanying chart.
If readings do not approximate those in the chart, the sensor may be faulty
