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Old 05-27-2014, 11:31 AM   #1
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6.0 PSD engine fan clutch override switch

Normal road and highway driving, all my temps are fine (as should be expected). The PCM does a great job of handling the temperatures during the conditions that Ford likely designed it for and efficiency is probably a heavily weighted parameter in whatever algorithm controls the fan speed during those conditions.
But when I'm cruising around on forest roads, or slow moving trails, my water, oil, and trans temps tend to stay quite a bit hotter (not out of the acceptable range, but hotter). Of those, the TFT is the most worrisome. I'm pretty sure no one would disagree that it's due to lack of air flow. When the fan kicks on at 215 ECT, everything cools down. Generally under these conditions, I'm not particularly concerned with squeezing every inch of progress out of each drop of fuel, so I wouldn't mind if the engine turned the fan all the time.

Creating an option to allow me to engage the engine fan when I want should do the trick.

I've seen this mod mentioned briefly in a few posts around here but never in detail. It's discussed here too: http://www.ford-trucks.com/forums/11...hich-wire.html

Here's my regurgitation of what I've read:
Basically, the PCM varies the fan speed by heating the viscous fan clutch at a duty cycle with a PWM signal. In a given time segment, the more of that time the heater is on, the hotter the clutch fluid gets, the harder the clutch engages, and the closer the fan speed matches the engine speed. The PWM does the duty cycle switching on the ground connection of the heater. 100% duty cycle means that the ground is always connected and the fan is directly coupled to the engine output shaft. Manually grounding the clutch heater will make the clutch behave as if the PCM has told it to go all in.

Wiring the override switch in parallel with the factory signal path means that when the switch is open (not grounded), the factory systems will behave normally.

The mod is reversible so I thought I'd give it a try.

There's a connector on the top towards the drivers side of the fan shroud. On the harness side of that connector is a blue wire. I cut back the split loom and added a splice with a spade terminal to this wire. Then I wrapped it all up in self-fusing tape. The spade terminal makes this still function as a connector when I need to remove things while working on the engine.




I routed a wire (connected to the new terminal) down next to the oil dip stick tube until it gets near a large wire harness under the brake booster, then along that harness, under the coolant degas bottle, then through the firewall. I had no luck using an existing feedthru, so I just made a new one. I applied a triple layer of heat shrink over the wire then some hot glue to keep it from chafing on the hole. In the future, if I need to route more wires through this spot in the FW, I'll cut this one, terminate it in some kind of bulkhead connector, and install that in the same spot.

To access all that, I had to temporarily move the power steering fluid reservoir, the coolant degas bottle, and disconnect the upper radiator hose from the radiator (only a dribble of coolant came out so it wasn't messy at all).

Under the dash, I routed the wire over to a SPST switch I put over near the High Idle switch. The other side of the switch is connected to ground.



The switch has an LED to indicate when it's on, but since the connection I'm making is ground and not power (and I don't want to send 12V to the fan ground...), the LED doesn't work. I'm still thinking about how to make this happen, but for now, it doesn't bother me. The round bezel does though...

Test drive time.
I took my usual "get hot enough to be worth it" route and the switch definitely makes the fan behave as advertized. When you activate the switch, the increased noise from the fan is noticeable after 30-60 sec. Standing outside the van at idle, I expected to hear a "whoosh" when the fan engaged (like an electric fan). It didn't do that and it twisted my brain for a second. Then I remembered that it's not an electric fan and it's noise is proportional to engine speed. I throttled up and then the noise was what I expected. Basically, it sounds the same as it does when you're in traffic and that fan comes on.
No engine codes so far.

I never reached conditions that would have made the fan come on normally, but the few times I manually switched it on, the ECT dropped quickly. I also was never in a situation where the transmission would heat up, so I can't report on that yet.

I'll update after some offroad driving.

For reference, my van is a 2006, has an Aluminess bumper, billet grille, big driving lights, and no auxiliary air vents (yet).
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Old 05-27-2014, 01:05 PM   #2
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Re: 6.0 PSD engine fan clutch override switch

What a great post and explanation. This one's going into the file cabinet for future reference!
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Old 06-09-2014, 07:07 PM   #3
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Re: 6.0 PSD engine fan clutch override switch

I did your mod this weekend. Great, it comes on easily and I will post more after the Nor Cal Meetup this weekend. It really makes alot of airflow compared to stock.

Paul
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Old 06-10-2014, 06:39 AM   #4
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Re: 6.0 PSD engine fan clutch override switch

You can keep the trans temp down by keeping the revs above 2000, thus essentially locking the torque converter. To do that, I always use low range when off road at low speeds. You could also downshift the trans, but low range gives more gear selections at low speeds.

Mike
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