OEM Elec Fan coming on too soon.

About 6 months ago, my factory electric fan started going on and off randomly at below 200* and continues to do so, even in winter. I've had a lot of overheating problems in the past, which are now solved, and the fan always used to come on right at 218* like it was supposed to. I've disconnected it for winter use, but want to resolve this before spring comes around, since I don't like the fan always going on when it's not supposed to. I feel like my temp guage is working Ok, since the engine is not very hot when the elec fan goes on. Any ideas? Seems unlikely that the ECU is just farting overheating signals to the fan. Is my ECU temp sensor the same one used by the temp guage? If not, then that one could be bad I guess. Any input is appreciated.

Well remember the ECU will run the fan with the A/C, and when the defrost on as the compresser cycles on/off.

Planetcat said:

Is my ECU temp sensor the same one used by the temp guage?

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Yes for '96+. The coolant temp. sensor (CTS) that sends an input to the ECU to trigger the electric fan to switch on is in the t'stat housing and it also operates the gauge.
The CTS could be faulty or the wiring/connector attached to it could be intermittently shorting out especially if there's a lot of moisture around. Remove the connector, clean it, and make sure the wiring insulation isn't cracked.

I'm going with what Scoobydoo suggested. Many people don't realize that when the heater controls are set to DEFROST the a/c cycles to dry out the air inside the cabin. This is not a malfunction, it's supposed to work that way and most American cars are set up that way.

Dr. Dyno said:

Yes for '96+. The coolant temp. sensor (CTS) that sends an input to the ECU to trigger the electric fan to switch on is in the t'stat housing and it also operates the gauge.
The CTS could be faulty or the wiring/connector attached to it could be intermittently shorting out especially if there's a lot of moisture around. Remove the connector, clean it, and make sure the wiring insulation isn't cracked.

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On a 96 there are 2 sensors,the one in the t-stat housing for the engine comp. and 1 in the back of the head for the temp guage in the dash.
The wifes, 98 has only the sensor in the t-stat housing.Not sure on a 97.
Wayne

Wayne Sihler said:

On a 96 there are 2 sensors,the one in the t-stat housing for the engine comp. and 1 in the back of the head for the temp guage in the dash.
The wifes, 98 has only the sensor in the t-stat housing.Not sure on a 97.
Wayne

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'96 was a crossover year so early '96 models may have engines that were built in '95 which have the 7120 head. The 0630 head was introduced some time in '96 and that doesn't have a port for the gauge sending unit.
As Eagle and Scooby correctly said, the electric fan WILL cycle on/off if you have the heater control set to defrost.

Dr. Dyno said:

'96 was a crossover year so early '96 models may have engines that were built in '95 which have the 7120 head. The 0630 head was introduced some time in '96 and that doesn't have a port for the gauge sending unit.
As Eagle and Scooby correctly said, the electric fan WILL cycle on/off if you have the heater control set to defrost.

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How does one tell which head they have? I'm so glad I have a 96! For some things it's 91-96, and others it's 96+ and others I have seen say "depends on when during the year your 96 was built"! Does the VIN # suggest what I have, or can I find this # somewhere else? Thanks for any input!

-Mike

if your ac/defroster/heater/vent or any climate control is on that fan will run on and off every 15-20 sec.
pete

Dr. Dyno said:

Yes for '96+. The coolant temp. sensor (CTS) that sends an input to the ECU to trigger the electric fan to switch on is in the t'stat housing and it also operates the gauge.
The CTS could be faulty or the wiring/connector attached to it could be intermittently shorting out especially if there's a lot of moisture around. Remove the connector, clean it, and make sure the wiring insulation isn't cracked.

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Dr. Dyno gets the prize. Faulty wiring connector was intermittently shorting. Replaced it and all is well for warm weather Spring wheelin'.

Planetcat said:

Dr. Dyno gets the prize.

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:cheers: