It has happened to me! (Dreaded Fan Sensor - Crumbling Hose!)

[HeatXfer]

I did carefully reach down and touch the sensor with the engine running to feel for vibration. When I applied a slight forward pressure to the sensor the clutch kicked in engaging the fan! It was already spinning but it picked up a great deal of velocity. I am still not sure if my actions triggered it, or it was coincidence. But I monitored it over several minutes and it would engage and disengage over just a few seconds, as in 15-30 seconds at a time. This at idle.

I did so to insure there was no undue pressure on the bearing from my new hose. It moved freely.

Hey, that's great! Was the fan operation just on/off, or could you feel it ramp up? I thought with a PWM there would be a gradual increase/decrease in speed and not just all or nothing.

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[TJC]

Hey, that's great! Was the fan operation just on/off, or could you feel it ramp up? I thought with a PWM there would be a gradual increase/decrease in speed and not just all or nothing.

It would vary in speed, not binary at all. Some times just low speed other times much faster, then slowly come to a stop Idle speed.

 

[HeatXfer]

It would vary in speed, not binary at all. Some times just low speed other times much faster, then slowly come to a stop.

Ahh, very good. Would it come to a full stop?

 

[TJC]

I am not sure it did, but easy enough to check tomorrow.

 

[airline tech]

The engagement to disengagement full cycle = 30 seconds to 2 minutes (spec)

Depending on what source you use for testing:
Ford Manual's - are not helpful as they give no guidance for actual testing of fan speed itself.
Only details - Wiring checks

Use Scan Tool - Monitor RPM and FSS
Increase RPM to 3500 RPM
FSS - (Less than 600 RPM)
Listen for Fan Disengagement

Detailed Ops Description is nill from Ford Manuals But:

What it does not tell you, is the level of engagement is dependent upon:
Engine Temp
Trans Fluid Temp
AC Request

Scan Tools - Allow Bi-Directional Control - To command.
0% = Disengaged
100% = Engaged
For Testing, but Ford does not cover this.
But when watching the Live Data PID's, you just watch for increasing FSS as you command it up the scale to 100%

 

[TJC]

I didn't time the fan on time, but it wasn't long, and the speed varied. It could easily have been 30 seconds. The jet engine rush of wind died down pretty quickly, and then the fan cycled in short low speed durations. Without a meter on the power line or ground it is hard to know if the power dropped completely or if the fan just slowed.

I'll visually check it shortly and report back.

 

[TJC]

OK, just got back in from a crisp 40F morning monitoring the fan during warmup. The truck is garaged. I started it and pulled it out doors, then raised the hood and watched the fan from the drivers side tire.

After the normal initial rather long fan spin up, the clutch cycle never exceeded 15 seconds. From stone cold to fully warm the fan cycles were separated by several minutes and were as follows (in seconds) - 15, 15, 12, 10, 5, 5, 2, 2, 2.

The fan never fully stopped, but it was obvious when it went to idle. the engagement did not appear to be abrupt based upon wind noise, with gradual increase/decreases. I saw no movement of the sensor or the hose.

The warmup was uneventfully normal. I have no idea about what to say about the Ford Engagement Cycle, but my truck did not behave in that manner (No minimum of 30 seconds on).

 

[TJC]

The next time I drive any distance I will monitor the fan cycles once I arrive home to see if there are any differences from what I just reported.

 

[HeatXfer]

Wow, I truly appreciate your commitment to the deep-dive!

My guess is that even if the fan clutch control called for zero fan operation, there is still enough drag in the clutch itself that the fan would never come to a complete stop.

 

[TJC]

My guess is that even if the fan clutch control called for zero fan operation, there is still enough drag in the clutch itself that the fan would never come to a complete stop.

I came to the same conclusion. It is spinning but not under load. It still moved air. If the hood had been closed you would not have known it was spinning.

 

[airline tech]

OK, just got back in from a crisp 40F morning monitoring the fan during warmup. The truck is garaged. I started it and pulled it out doors, then raised the hood and watched the fan from the drivers side tire.

After the normal initial rather long fan spin up, the clutch cycle never exceeded 15 seconds. From stone cold to fully warm the fan cycles were separated by several minutes and were as follows (in seconds) - 15, 15, 12, 10, 5, 5, 2, 2, 2.

The fan never fully stopped, but it was obvious when it went to idle. the engagement did not appear to be abrupt based upon wind noise, with gradual increase/decreases. I saw no movement of the sensor or the hose.

The warmup was uneventfully normal. I have no idea about what to say about the Ford engagement cycle, but my truck did not behave in that manner.

The Ford engagement cycle I posted:
Was for a Pinpoint Test of Fan Stays Engaged, which is the only test it has for a (No-Code) test with the sensor plugged in.
The time frame is (Within) 30 sec to 2 minutes.

Here is a link to a video on Fan Clutches:
Scroll to about 47.0 Minutes.

Fan Clutch Operation and Diagnosis (youtube.com) ----Basic Ops Ford

 

[TJC]

The Ford engagement cycle I posted:
Was for a Pinpoint Test of Fan Stays Engaged, which is the only test it has for a (No-Code) test with the sensor plugged in.
The time frame is (Within) 30 sec to 2 minutes.

Here is a link to a video on Fan Clutches:
Scroll to about 47.0 Minutes.

Fan Clutch Operation and Diagnosis (youtube.com) ----Basic Ops Ford

Thank you for the clarification! It is appreciated.. I was beginning to think my truck was an abnormal deviant, or perhaps I did something a little bit wrong.

I just downloaded that video to add to my Ford Diagnostics and Maintenance library

 

[airline tech]

Wow, I truly appreciate your commitment to the deep-dive!

My guess is that even if the fan clutch control called for zero fan operation, there is still enough drag in the clutch itself that the fan would never come to a complete stop.

Yes - It will never come to a complete stop - like an electric cooling fan.

Ref: The Ford Test @ 3500 Eng RPM, Fan Speed will be about 600 RPM, when fully disengaged (0%)

Ref: Value Charts for the Ranger for FSS (Fan Speed Sense)
Hot Idle: 450 RPM
30 MPH: 450 RPM
50 MPH: 575 RPM
So, what this shows is the Fan Disengaged

Now factor in, variables.
AC (On)
Temps of Trans and Engine
IAT (Intake Air Temps)

If the engine is running hot - The PCM will command engagement of the clutch, while factoring in the Ram Air (Effect) of the airflow across the fan.
This is Desired Duty Cycle (in the PCM parameters) (0-100%)
If needed the PCM will pulse the fan speed higher
Higher (will increase fan speed) to get more air flowing to cool the engine.

 

[HeatXfer]

Thanks AT! While your explanation cleared up my understanding of the circuits, that video is the cherry on top.

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