Modified Fan Clutch

77mustard40

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6 or 8 years back I was having some overheating issues, mostly after prolonged highway speeds or after exiting a highway. Temps would climb above the first bar of our dummy temp gauges towards the second bar. I ended up pulling the fan clutch and separating the halves and the silicon had turned into a dark brown sticky syrup. I cleaned it out best I could and refilled with half 3,000 CST and half 6,000 CST silicon, slapped her back together and the problem was solved.

Late last summer i started to see signs that my temps were rising again, but were not as concerning. I did a full flush and fill with new coolant in the fall and just bought a new Aisin fan clutch. I think my old rehabbed one could be the original and could be on its way out. Before I install it I’m curious to hear if anyone has modified their fan clutch like you see in the 80’s forum ( lowered opening temps and thicker silicon)? I’ve got some tubes of 8K, 10K and 15K CST on the shelf. Gets hot here in Texas so I’m thinking about cracking open the new one and beefing up the silicon before installing, any thoughts or experience? ‘77 original 2F here.

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Hi,,

A new Asian fan clutch is definitely in the right direction,,

As far as modifying the new Toyota part ,, I may try running it as is to gauge its cooling capacity to set a bench mark,,

How’s the rest of the cooling system ?


When I worked as a tech for the FJco in Miami Florida I had to work though a few 2fs that would run hot,, like real hot

Things I can pass along to help

A quick coolant combustion test to rule out a head gasket is always where I start,,

I personally have tried different viscosities in fan clutches ,, and it helped,, but was never the silver bullet I hoped it would be,,

What I found to be the biggest difference was a properly functioning cooling system

But that leaves lots to investigate

Ie
Thermostat …is it opening properly ?

Radiator … any internal blockages or abnormally cold spots ?

Fan and shroud condition,,

Water pump .. is it a Toyota pump? And if it’s an original,, how are the impellers?

Ignition timing / AFR s? excessive ignition timing and/ or lean carb mixtures will play a big affect to the heat the motor produces.

May have just given you more questions then answers lol but persistence overcomes resistance ;)
 
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77mustard40

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Hi,,

A new Asian fan clutch is definitely in the right direction,,

As far as modifying the new Toyota part ,, I may try running it as is to gauge its cooling capacity to set a bench mark,,

How’s the rest of the cooling system ?


When I worked as a tech for the FJco in Miami Florida I had to work though a few 2fs that would run hot,, like real hot

Things I can pass along to help

A quick coolant combustion test to rule out a head gasket is always where I start,,

I personally have tried different viscosities in fan clutches ,, and it helped,, but was never the silver bullet I hoped it would be,,

What I found to be the biggest difference was a properly functioning cooling system

But that leaves lots to investigate

Ie
Thermostat …is it opening properly ?

Radiator … any internal blockages or abnormally cold spots ?

Fan and shroud condition,,

Water pump .. is it a Toyota pump? And if it’s an original,, how are the impellers?

Ignition timing / AFR s? excessive ignition timing and/ or lean carb mixtures will play a big affect to the heat the motor produces.

May have just given you more questions then answers lol but persistence overcomes resistance ;)
Appreciate the long list of suggestions, but I’m pretty confident that I don’t have other cooling system issues. I don’t have any of the typical HG failure symptoms, and the rest of the system is in good shape. Flush last fall was uneventful, everything ran clear and clean including the block drain. I tested the new thermostat in a pot of water before installing after the flush so I’m good there.

My question is more of a survey to see if any of the 40’s owners have stiffened up their fan clutches. Granted there are subtle differences in the aerodynamics of a 40 and an 80, so there may no real reason to modify the 40’s fan clutch.

I dug back and found some pics I took when I refreshed my old clutch in ‘14 and it looks like the only mod might be to change out the oil, I don’t see the set screws that exist in a later model clutches that allow you to dial in the temp that they open. I may just go with the new one as is but crack my old one open just to see what it looks like. I know from prior experience with my old one that they can be refreshed and I know from my 80 series blue hub clutch that increasing the viscosity of the silicon makes a big performance difference.

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graham5david

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Guys do this in the 80 crowd tp their fan clutch alot. I did mine in my 80. It helps. But I thought I had a properly functioning coolant system too. It was a bandaid to the real problem. I emptied the coolant and ran it with distilled water and some liquid cascade for a day. I was absolutely amazed at the sludge and crap that came out. I did that for 2 or 3 cycles until clear. Then I put a new t stat and water pump on, put new coolant in and never over heated on me again. You may or may not have some sludge in the engine or radiator. I wouldn't assume your coolant system is in good shape. I had even changed my radiator prior to getting rid of the sludge with no improvement. I'm sure there is better options for getting rid of sludge than liquid cascade and distilled water too.
 
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That cascade flush is an old trick, and it usually works wonders-
 

77mustard40

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Yeah I’m not worried about the flush, flushed with thermocure and distilled last fall and it was really pretty clean. Ran it with distilled for a couple of days, drained and refilled with distilled twice to get it all clean.

I did tear it down today and have decided to replace the water pump, looks like mine may be the original. Ordered one from Cruiser Outfitters. Rad is less than 10 years old and still looks solid, cleaned it up with the pressure washer today. My splash pan has some surface rust on it so I’ll clean it up and paint it while waiting for parts.
 

77mustard40

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Just to close this thread out since it bugs me when I search, find a pertinent thread only to find it’s a dead end. I ended up replacing the water pump which I think was original (I’ve had the truck since ‘85). Bolts into the water jacket were a PITA and I spent quite a bit of time chasing those threads and sourced new hardware. Removed the gasket on the water pump and reinstalled with The Right Stuff RTV along with the gasket between the pump and block.

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77mustard40

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I also found evidence of a leak in my radiator so I hit the deck for a new one. The leak may have been a big part of the original climbing temp issue because it probably wasn’t holding pressure. I went with a Champion 3 core based on lower cost and the fact that we see some high temps here in Texas. Other than replacing the petcock style drain, install was straight forward. Went ahead and dropped a new thermostat in and replaced a few hoses that were starting to show signs of age. After a couple of drives I think I’m good, will still get it out for an hour or so today in the 100+ temps to make sure.

In the end I did not open and replace the silicon in the new fan clutch.

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mattressking

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Late to the party but heating up at highway speeds aren’t relative to fan clutch issues, the air forced on radiator cools the truck down and unless you’re on a steep climb, the clutch doesn’t come on. Radiator like you said is likely the issue if not the entire issue once properly bled
 

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