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

[airline tech]

The more complicated the plumbing, the easier it is to stop it up!

Yes, I hate VREF Circuits as there is not a full diagram of just the VREF (By-Itself)
It spreads across multiple pages. (and you have to pay attention to the splices)

A shorted VREF circuit is the most difficult to Troubleshoot.
Disconnect each sensor (1) at a time to find the fault (location) - Between A-B sensor.
Then check wiring between them - if good then confirm which of the 2 sensors is killing the circuit.

It's like a string of old Christmas lights, one goes out they all go out.

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[TJC]

I woke up this morning with what I think is an inexpensive and elegant solution to fan clutch hose issue that I believe corrects the problem. It is quick and easy to do if you have a tap and die set.

I removed my old first pass attempt and the engine stud bracket. I then ground down the lip on the original stud, filed it smooth with the stud surface and then polished the edge with a cloth wheel.

I then drilled out the stud and tapped it to 1/4" 20 threads .4" deep. I found a nice stainless steel button head bolt and screwed it into the stud. The stud is a solid piece so only drill as deep as you need to to secure the bolt. If you have a long bolt, the easiest way to cut it to size is to use a portable grinder, but before beginning, screw a nut to the top of the bolt and insert into a vice tightening on the nut. Be sure the bolt end is protruding right up against the nut. Then make the cut. Removing the nut will clean the threads.

Here is the bolt used and the stud bracket removed. The bolt head is the same diameter as the original lip, but has a very nice smooth polished radius to it, perfect for a hose dual flare replacement.

Here is the bolt installed into the stud.

And here it the completed project. I wanted to protect the cable from the hose clamp edges so I used 1" section of fuel line hose to route the cable much like the original cable standoffs. I still have a bulge in my silicone cable where the head of the screw is, but I am confident that the stress to the hose has been minimized. Hint: The stud bolt on my truck had never been removed and it was only snug. When I reinstalled it, I was careful not to over tighten the bolt. it is going into aluminum threads.

If the retainer lip on the stud is part of the problem, (as well as the cheap hose), and I think it is, then the problem can be put to bed. I guess In a few years I will know if this has worked.

- T

 

[pboggini]

I woke up this morning with what I think is an inexpensive and elegant solution to fan clutch hose issue that I believe corrects the problem. It is quick and easy to do if you have a tap and die set.

I removed my old first pass attempt and the engine stud bracket. I then ground down the lip on the original stud, filed it smooth with the stud surface and then polished the edge with a cloth wheel.

I then drilled out the stud and tapped it to 1/4" 20 threads .4" deep. I found a nice stainless steel head button bolt and screwed it into the stud. The stud is a solid piece so only drill as deep as you need to to secure the bolt. If you have a long bolt, the easiest way to cut it to size is to use a portable grinder, but before beginning, screw a nut to the top of the bolt and insert into a vice tightening on the nut. Be sure the bolt end is protruding right up against the nut. Then make the cut. Removing the nut will clean the threads.

Here is the bolt used and the stud bracket removed. The bolt head is the same diameter as the original lip, but has a very nice smooth radius to it, perfect for a hose dual flare replacement.

Here is the bolt installed into the stud.

And here it the completed project. I wanted to protect the cable from the hose clamp edges so I used 1" section of fuel line hose to route the cable much like the original cable standoffs. I still have a bulge in my silicone cable where the head of the screw is, but I am confident that the stress to the hose has been minimized. HInt: The stud bolt on my truck had never been removed and it was only snug. When I reinstalled it, I was careful not to over tighten the bolt. it is going into aluminum threads.

If the retainer lip on the stud is part of the problem, (as well as the cheap hose), and I think it is, then the problem can be put to bed. I guess In a few years I will know if this has worked.

- T

I was thinking of something similar but I was thinking of having a through bolt with the nut on the other side with flat washer to spread the load. I do like the addition of the fuel hose to route the harness through. I'm going to do that too! Oh, and good to know that's a stud bolt and not just a nut you can pull off. Interesting that they do that as I'm not sure what the stud is for especially since it has to have that rubber piece on it, seemingly to protect it or protect something from it?

 

[TJC]

The stud holds the wire loom in place. You need it. Don't cut the plastic cable retainer (rubber piece). I used a pair of curved needle nose pliers to assist in removing it from the stud. It slides back on easier than it comes off.

If you look closely at the image below, on the left edge center you can see the cable and the plastic retainer on the stud.

 

[airline tech]

I will say that now that I realize the correct fan rotation, it is much easier to visualize.
How the tube breaks and sensor is able to rotate, which pulls the harness down to the pulley bolt heads (pulls the harness) and the fan attaching Hub Nut (rubs the harness)
The harness gets caught on the pulley bolt heads and rips it apart. ,
The sensor after the harness is ripped apart, springs back the opposite way, thus the reason for all the pics (after damage) show it spun the other way. (like a sling shot)

This was my (misleading) point of rotation direction and not thinking of actual engine rotation.
The resting position of the damaged sensor.

So, 1/2 of the issue is resolved and answered.

So now we only have one question to be answered:

What wear or failure or operational control - causes it to rotate?
Due to the fact, that one could disconnect the hose or have the hose broken and the sensor will remain stationary without rotation and wire harness remain intact.

It has something to do with the amount of play in the sensor and the friction between the sensor and the shaft it rides on.

 

[TJC]

I will say that now that I realize the correct fan rotation, it is much easier to visualize.
How the tube breaks and sensor is able to rotate, which pulls the harness down to the pulley bolt heads (pulls the harness) and the fan attaching Hub Nut (rubs the harness)
The harness gets caught on the pulley bolt heads and rips it apart. ,
The sensor after the harness is ripped apart, springs back the opposite way, thus the reason for all the pics (after damage) show it spun the other way. (like a sling shot)

This was my (misleading) point of rotation direction and not thinking of actual engine rotation.
The resting position of the damaged sensor.

So, 1/2 of the issue is resolved and answered.

So now we only have one question to be answered:

What wear or failure or operational control - causes it to rotate?
Due to the fact, that one could disconnect the hose or have the hose broken and the sensor will remain stationary without rotation and wire harness remain intact.

It has something to do with the amount of play in the sensor and the friction between the sensor and the shaft it rides on.

I honestly think most of the problem is the hose quality and connection method. The rotation of the shaft transfers some of that energy through the bearing. Disconnect the sensor and watch it (the sensor) spin with the engine. It doesn't take much resistance, and unless that bearing is levitating (and it's not) there is going to be some amount of torque transfer. As the bearing ages/wears and grease hardens, the torque will increase. Throw in a marginal batch of bearings or hoses for good measure.

Each time the clutch engages / disengages it is stressing that hose, and the weak points (IMO) are at the connections, specifically right where the flex point is weakest. Bend/Flex anything enough and it will break. The contact point on the stud end is very small, and the hose itself is delicate. A recipe for failure.

That's my theory.

 

[HeatXfer]

Each time the clutch engages / disengages it is stressing that hose, and the weak points (IMO) are at the connections, specifically right where the flex point is weakest. Bend/Flex anything enough and it will break. The contact point on the stud end is very small, and the hose itself is delicate. A recipe for failure.

That's my theory.

Remember, the fan hub rotates as long as the motor is running so other than starting the engine, the fan sensor is not subjected to any sudden torque or shock. As I said in a previous post, I observed the assembly during engine start and when it cycled on temperature and there was little to no detectable movement of the hose or sensor. I didn't hold it to check, I'm not that brave (or stupid as the case may be). There is a decent amount of high-frequency vibration at the hose's engine bracket, leading me to believe the failures are more due to fatigue that shock. Whatever drag there is between the hub and the sensor there's a steady pull on the hose while the engine is running and I'm not so sure that's a big concern. Until someone here cuts their failed fan clutch open we're not going see exactly what the bearing surfaces are between the hub and the sensor: plain or ball?

I'd love to see the sensor cut open to see what's going on inside.

 

[got3fords]

Remember, the fan hub rotates as long as the motor is running so other than starting the engine, the fan sensor is not subjected to any sudden torque or shock.

But isn't that why there is a overrunning clutch on the alternator?

 

[pboggini]

The stud holds the wire loom in place. You need it. Don't cut the plastic cable retainer (rubber piece). I used a pair of curved needle nose pliers to assist in removing it from the stud. It slides back on easier than it comes off.

If you look closely at the image below, on the left edge center you can see the cable and the plastic retainer on the stud.

Ah thanks. Yea I never looked that carefully at that as I was to going to remove it. Makes total sense why it's a stud bolt now.

 

[TJC]

You have a point... to a very large degree. However engaging the fan clutch does affect the engine RPM to some degree, even varying engine RPM when speeding up and slowing down changes the shaft spin speed. Not to mention the drag shock wave sent when the clutch engages, gears changing, AC cycling... all affect rates of change. Not to mention maybe the bigger affect of the engine rocking on its mounts when throttling up. In short, any vibration or movement.

Simply look at the design. Why use a light flexible hose? Why not run something more rigid, like aluminum or steel to anchor the sensor? I think the engineers intentionally designed cushion/flex into the system.

Like I said earlier, it's only my theory... and I could be "full of __ it! Kinda like playing "left out" in baseball!

 

[HeatXfer]

But isn't that why there is a overrunning clutch on the alternator?

I'm sure there's some relationship between the two; the OAD must limit some start-up shock to the fan clutch, but because that fan sensor "floats" on the shaft the shock it sees will be limited by the drag between the shaft and the sensor bearing. I think the overriding issue is with long-term exposure to vibration while the engine is running. The OAD pulley only limits vibration in the belt caused by lash/slap from changes in engine speed/belt velocity. Now, depending on how fast the PCM can react to sensor inputs and how fast the viscous clutch can react to the PCM signal, the fan clutch might dampen vibrations and shock caused by a sudden increase or decrease of engine speed, but that still doesn't account for stress seen by the hose.

 

[HeatXfer]

You have a point... to a very large degree. However engaging the fan clutch does affect the engine RPM to some degree, even varying engine RPM when speeding up and slowing down changes the shaft spin speed. Not to mention the drag shock wave sent when the clutch engages, gears changing, AC cycling... all affect rates of change. Not to mention maybe the bigger affect of the engine rocking on its mounts when throttling up. In short, any vibration or movement.

Simply look at the design. Why use a light flexible hose? Why not run something more rigid, like aluminum or steel to anchor the sensor? I think the engineers intentionally designed cushion/flex into the system.

Like I said earlier, it's only my theory... and I could be "full of __ it! Kinda like playing "left out" in baseball!

Well, someone with a sensitive strain meter or digital fish scale could put it in place of the the hose bridge and actually take some readings to see EXACTLY how much shock it's subjected too. Hmm, time for a Amazon search...

 

[TJC]

Maybe is just simple vibration, not torque induced at all.

 

[HeatXfer]

Maybe is just simple vibration, not torque induced at all.

Combination of both? Either way I'd love to find out

 

[TJC]

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.

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