92 FJ80 Overheating Going Uphill (1 Viewer)

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Hey, I have a 92 FJ80 that is overheating after about 5 miles going uphill.. I don't have any issues off road, around town or "normal" freeway driving - only when engine is taxed heading uphill.. Have ~ 2yr old radiator and I just changed water pump, thermostat, and fan clutch.. Still overheating.. Stumped..
 
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Did you use OEM parts, with the exception of the radiator?
Is your fan shroud in place and tightly sealed to the radiator?
 

Squash

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What temps are you seeing?
You should avoid O/D or select 3rd gear to prevent the tranny from hunting for gears as this creates lots of heat.
Also experiment with keeping rpms up and avoid lugging and engine uphill.
 
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What temps are you seeing?
You should avoid O/D or select 3rd gear to prevent the tranny from hunting for gears as this creates lots of heat.
Also experiment with keeping rpms up and avoid lugging and engine uphill.
I am not sure exact temps.. Gauge is usually pegged just below horizontal, then it starts to move up and just keeps going until I pull over to let it cool down.. I do see a bit of an impact if I turn heater on (front and rear).. However, my front heater doesn't seem to work (blowing luke warm air).. Possible heater core problem or ?.. I don't know if the heater core could be impacting the overheat as well.. Yes, keep it in 3rd during steady climbs and try to keep rpms up to maintain any type of speed..
 
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I am not sure exact temps.. Gauge is usually pegged just below horizontal, then it starts to move up and just keeps going until I pull over to let it cool down.. I do see a bit of an impact if I turn heater on (front and rear).. However, my front heater doesn't seem to work (blowing luke warm air).. Possible heater core problem or ?.. I don't know if the heater core could be impacting the overheat as well.. Yes, keep it in 3rd during steady climbs and try to keep rpms up to maintain any type of speed..
The front heater core sounds plugged, frankly. That could also be plugging the newish radiator.

I'd gently backflush just the heater lines until they run clear. I'd then gently backflush the radiator until it flows clear as well. It's more involved, but wouldn't be a waste of time.
 
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fan clutch.....i run thicker oil in OEM clutch...also alum. radiator makes a huge diff. vs brass/copper. Mine used to run hot on hill climbs, replaced radiator, fan clutch, waterpump, thermostat, now the temp stays below 200F on hill climbs with full AC...
 
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The front heater core sounds plugged, frankly. That could also be plugging the newish radiator.

I'd gently backflush just the heater lines until they run clear. I'd then gently backflush the radiator until it flows clear as well. It's more involved, but wouldn't be a waste of time.
Thanks for the suggestion.. Will give it a go this weekend..
 
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Hey. Still looking for some help.. I back flushed the heater core (not plugged) and broke down and replaced the 2-3 year old radiator.. I am still seeing the problem with over heating while taxing the engine going up hill for about 4-5 miles.. I have basically replaced everything in the cooling system.. Also with the back flushed heater core not being the problem, the front heater still isn't working (rear heater is working). The heating control / blend door and heater fan seem to be working fine.. I am not sure if these two issues are related but I thought I would throw it all out there.. Is over heating a "common" issue with 92's? Appreciate all the feedback received thus far and any other suggestions..
 
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Hey. Still looking for some help.. I back flushed the heater core (not plugged) and broke down and replaced the 2-3 year old radiator.. I am still seeing the problem with over heating while taxing the engine going up hill for about 4-5 miles.. I have basically replaced everything in the cooling system.. Also with the back flushed heater core not being the problem, the front heater still isn't working (rear heater is working). The heating control / blend door and heater fan seem to be working fine.. I am not sure if these two issues are related but I thought I would throw it all out there.. Is over heating a "common" issue with 92's? Appreciate all the feedback received thus far and any other suggestions..
Did you replace with OEM, or go for aluminum?

The common thing on the 3FE is that the stock radiator isn't an overachiever, so airflow is key. Sealing the fan shroud to the radiator is needed to force airflow through it, not just near it.

If that's done, then you have the fan clutch to consider. Does it turn easily, with the engine cold, or stiff? Does it roar at startup?

That said... The front heater not working tells me something still isn't right in the cooling system. How certain are you the system has been fully bled of air?
 
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fan clutch.....i run thicker oil in OEM clutch...also alum. radiator makes a huge diff. vs brass/copper. Mine used to run hot on hill climbs, replaced radiator, fan clutch, waterpump, thermostat, now the temp stays below 200F on hill climbs with full AC...
Do you mind sharing which radiator and fan clutch etc you put in? Driving back from Moab right now and we def had this issue climbing the hills around there. AC stopped blowing cold after some of the climbs as well
 
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Do you mind sharing which radiator and fan clutch etc you put in? Driving back from Moab right now and we def had this issue climbing the hills around there. AC stopped blowing cold after some of the climbs as well
The proper fan clutch for the 3FE engine is the green/aqua hub Aisin FCT-049. You did not specify what engine you have.
 
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The proper fan clutch for the 3FE engine is the green/aqua hub Aisin FCT-049. You did not specify what engine you have.
Sorry. I have a lx450. 1fzfe. I haven’t pulled mine out just yet to see which it is. I suspect it’s original. Honestly I never let the engine get to the red. I pulled over a ton. It looks like I have the original Radiator. So I am trying to decide if I just drain the fan clutch and toss in some 10000 CDT silicone lubricant in there to see if that fixes it.

but after 7 days at Moab. This is just part of what I need to address. 😂😂
 
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Do you mind sharing which radiator and fan clutch etc you put in? Driving back from Moab right now and we def had this issue climbing the hills around there. AC stopped blowing cold after some of the climbs as well
I put in a Ron Davis Alum. 2 row, and a Aisin Green fan clutch with thicker 15k oil and adjusted timing to open...
 
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Hey. Still looking for some help.. I back flushed the heater core (not plugged) and broke down and replaced the 2-3 year old radiator.. I am still seeing the problem with over heating while taxing the engine going up hill for about 4-5 miles.. I have basically replaced everything in the cooling system.. Also with the back flushed heater core not being the problem, the front heater still isn't working (rear heater is working). The heating control / blend door and heater fan seem to be working fine.. I am not sure if these two issues are related but I thought I would throw it all out there.. Is over heating a "common" issue with 92's? Appreciate all the feedback received thus far and any other suggestions..


Any news on this? I have the same problem. Overheating when drive up grades and hills. Radiator, Thermostat, Fan Clutch and all hoses have been replaced. Still same issue.
 
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Have you guys that replaced the fan clutch done the 7-20k cst fluid change or just running it as is?
The 3k fluid won't spin it nearly as fast as 10k, especially so at higher rpms. Which kind of defeats the purpose of running up hills at 4000 rpm if the fan isn't spinning up that fast too.
I went with 7k cst fluid to go easy on my 25 year old plastic fan, (which honestly I should just replace), but the original Toyota Supras came with 20k cst fluid according to some of the old modded fan clutch threads on here.

If you want the math, here it is for a rotary viscometer, of which our fan clutches are basically a Russian nesting doll of viscometers:
1605089170774.png

Conveniently enough, the unit cST is already the kinematic viscosity of the silicone oil, and is a linear scale.
Also, silicone oil is extremely consistent in viscosity even under large temperature changes. (which is why it is used in fan clutches)
equation:
kinematic viscosity is the lowercase Greek letter Mu
T is the driving torque
Ri is the inner journal radius
Ro is the outer journal radius
w is the rotational velocity relative to the clutch pulley
L is the length of the journal
1605086622050.png


As you can see, the torque increases linearly with the kinematic viscosity and the rotational velocity. So for a given torque (aka a specific fan rpm), the "slip" will decrease proportionally to an increase in viscosity.
So lets pretend you want to drive the fan at 3000 rpm, and for the stock 3k cST fluid you need the pulley at 4000 rpm to do so. (hypothetical, I have no clue how much slip it actually has for a given rpm). A clutch with triple the viscosity, or 9k cst fluid, would only need to spin at 3333 rpm to achieve the same fan rpm/amount of airflow through the radiator.

In reality, you would still run it at 4000 rpm, and the fan would increase in speed by some amount - but fans are much harder to calculate.
(the torque required is a square relation, just like how aerodynamic drag increases by velocity squared, but it also depends on other variables like the pressure drop due to the restriction of the radiator as more air flows through it, etc)
 
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The OEM Aisin green hub FCT-049 fan clutch is very robust right out of the box. It has more internal shearing surface than the blue hub version used in later engines.
With all OEM parts in proper working order, the factory cooling system should have no issues keeping those 155 wild horses in check.
 

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