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Rpms and fan clutch


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Would like to have deeper understanding of my fan clutch. As I understand it, the fan will be disengaged at high rpms. The assumption being that high rpms equals enough ground speed and air flow through the rad to make the fan redundant. 

So is this a gradual process or a on/off? At what rpm/range of ROMs does this happen? 

I have 83 Sunrader with a stock 22R and 4spd manual. I am not currently having any overheating issues, but I could imagine a long hill climb in 2nd with high rpms but limited ground speed/airflow. Knowing the rpm fan cutout would help me manage this scenario.


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my 84 has a thermal fan clutch. it engages at a predetermined temp controlled by a bimetallic  coil mounted on the front of the clutch. 

   if your fits this description, it shouldn't decouple due to rpm

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It's going to howl cold for a bit it's the gook inside of the clutch (it's thick) it warms up fast and goes back into the normal mode. 

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Thanks everyone. This is great. As far as I know it's a stock can clutch. 

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The little 22 motors are worked pretty hard in these and head gasket issues are not uncommon.  So getting out in front of it BEFORE that happens, is a pretty smart idea!  As others have said, the fan clutch on yours is solely temperature based.  It is pretty common for fan clutches to "whoosh and roar" for a minute or so on start up, and then quiet down.      


Go over your cooling system closely.  Verify correct thermostat operation.  If you decide to change it, you can find one slightly cooler than stock.   


If your radiator needs replacement you can get aluminum radiator kits that also replace the fan clutch with an electric thermostatically controlled fan.


Make sure your fan shroud is there.  Some of the older Toyotas have two shroud parts.   


Make sure the coolant is nice and clean/fresh.  Might even be worth running the nice Toyota coolant in it.  It seems to last longer than the green stuff anyways.  If it needs a flush, I would put the Toyota red/pink back in myself.


I LOVE a product made by Redline called "Water Wetter" and can't recommend it enough!  I have had some pretty high horsepower Volkswagens that suffered from cooling system issues.  Using Water Wetter significantly improved the cooling system efficiency.  It alters the surface tension to make the heat transfer more effectively.  My 1977 Rabbit went from overheating at lights, to being okay parked on the highway on a hot day stuck in traffic.  I will be adding that to my 4Runner cooling system here shortly after I replace a few other things, like the thermostat and flush the coolant.  


Most importantly, keep a close eye on temperatures.  I have a super cool gauge from a company called Perfect Tuning.  It lets me configure audible and visual alarms for specific parameters I want to keep an eye on.  It is meant to be used in a standalone engine management situation with a MegaSquirt.  But it does accept sensor inputs directly, I think up to 4.  I will be using to in my 4Runner to monitor Air Fuel Ratio, coolant temp, transmission temp, and maybe transfer case temp.  Even if I don't go 'squirt the truck.  


I would imagine there are similar options out there for MUCH cheaper that would at least give you a configurable alarm for coolant temp.  A quick look and I am not finding any, but they have to be out there...  


And if you have any doubts or concerns about your headgasket, a block test is very easy to do and nice peace of mind.  





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 Thanks for the great information. I will be replacing my rad this season - hopefully with a copper/brass 3 core - and I wanted to ensure my fan clutch was doing what it should. 

Edited by akwcanoe
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