The ROAR of the fan...

I bought an '02 Taco/regular cab/4 cyl/auto/2wd a couple months ago. Good truck!

So, I've notice the mechanical engine cooling fan makes a lot of noise and blows a heck of a lot of air--the radiator is way over-cooled for street driving. Every time I step on the gas, I hear the roar of the fan. The viscous fan coupling and the clutch are functioning properly--when the motor is off, you can turn the fan back and forth. Compared to the mechanical fan in my Audi, the fluid coupling is REALLY STIFF...I'll bet it takes a full 1 hp to turn the fan at 3k rpms. So, I've been stewing about how to fix it: 1. install a VW/Audi fan clutch or 2. install an electric fan. Putting in a VW/Audi fan clutch would take WAY to much tinkering/machining. Putting in an electric fan would cost more than I want to spend and would take a fair amount of tinkering.

This morning, I woke up with a flash of inspiration: replace the fluid in the viscous coupling. An hour after starting the job, the deed was done and NO MORE ROAR OF THE FAN!

1. Remove the lower fan shroud--2 metal clips.
2. Remove the fan--Unscrew the (4) 12 mm nuts holding the fan onto the pulley. Wiggle the fan out from underneath the truck.
3. Remove the plastic fan blades from the coupling/clutch--(4) 10 mm nuts.
4. Here's the tricky part remove the 8(?) #3 phillips head machine screws that hold the 2 halves of the fluid coupling together. They are TIGHT. I soaked them w/ WD-40, tapped the heads w/ a hammer and cursed them adequately. A little heat from a torch might have helped, but I didn't think of that til now. I clamped the coupling to the workbench and broke the screws loose w/ a hammer and small cold chisel.
5. Separate the 2 halves of the coupling--a little coaxing, a little tapping and they separated. Do this on a piece of newspaper...you don't want to spill oil on your workbench.
6. The fluid coupling is filled w/ a viscous oil that is the same consistency as STP, which is 50 weight oil + zinc additives (remember that stuff? "STP is the racer's edge"). The fluid in the coupling is slimy, sticky and looks like honey, but has no smell (synthetic oil?). No wonder the fluid coupling is so stiff! Scrape/drain/wipe as much of the fluid out as you can. It's about 1-2 ounces. Try not to dislodge the large round black oil seal--it's oversized and a bit tricky to get in place once removed.
7. Wipe everything clean with a paper towel.
8. Pour about 1.5 ounces of synthetic motor oil into the bigger half of the coupling. I used 10W-30 Mobil-1, cuz that's what I had on the shelf. It gave the exact amount of "freewheeling" I was looking for. I THINK regular oil would be fine, but synthetic is kinder to seals.
9. Line up the two halves and install the phillips screws. When you put it back together, you'll notice that the fluid coupling spins MUCH easier with lighter oil in it.
10. Install the fan blades on the coupling.
11. Install the fan & coupling back on the engine.
12. Everything tight? Start the engine and notice how much quieter the fan is and how much quicker the throttle response is! Woo-Hoo!!!

The fan still blows plenty of air, so I'm sure it will cool the engine adequately. And if it gets too hot, the fan clutch will kick in.

Cost of this mod: 1 hour and 40 cents worth of motor oil.

 

This is very interesting. I thought that the fluid acted as the clutch, i.e as it heated up it transferred more torque to the fan blades, but your explanation is that there is a separate physical clutch in the fan?

Time to research this a bit.

 

If anyone is interested, I found this very educational.

http://neuralfibre.com/paul/4wd/tuning-and-understanding-your-toyota-viscous-fan-clutch

 

Yes, I believe there is a physical clutch inside the fan clutch mechanism. The curly-cue thing on the front of the coupling unit is a bi-metallic strip. As the radiator heats up, the bi-metallic strip heats up and starts to "uncoil", which turns the mechanism inside the clutch engaging "direct drive" on the fan. In the "old days" (1970's) you could hear the clutch engage and the fan got much louder. After the radiator cooled down, the clutch disengages and the fan is allowed to "slip" or freewheel and it gets much quieter, because it's moving less air.

 

The link I attached describes the bi-metal mechanism, but explains that the level of engagement is influenced/controlled by the amount of fluid that is circulated back through the valve attached to the bi-metal strip. The author in the linked page actually complained that the fluid level is often too low, and thus the fan doesn't turn fast enough/ engage soon enough in toyota fan clutches. The opposite of your issue.

 

That is a great idea. You are crazy; I like that.

 

I can't hear my fan at all.

 

Is there anyway to make a orange fan clutch into a hd clutch like the green one? I still have my original orange clutch. Nine years ago I swapped the orange for the green.