Start-up Roar is gone

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HuyFZJ80

HuyFZJ80

Joined
Nov 2, 2024
Threads
8
Messages
76
Location
Sacramento
My 94’ has always started with a strong roar, running up to 1800rpms and then holding at 1600rpm for a bit until she slows down to 650rpm when warm.

Yesterday, on cold start, it only rev’d to 1200rpm for a split second, then held at 1000rpm for a bit, and ended at 650 when warm.

My assumption is that my fan clutch is toast. Is there anything else that could potentially cause this before I dive in and buy a blue fan and mod it? Thanks all!
 
Mag71k5 said:
Your instinct is probably right, but you could always further diagnose it with a thick roll of magazines, to see if you can stop the fan clutch when it’s at operating temp.
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The fan doesn’t spin freely when the engine is either cold or hot. I’ll give the magazine method a try before I start to tear into things
 
HuyFZJ80 said:
The fan doesn’t spin freely when the engine is either cold or hot. I’ll give the magazine method a try before I start to tear into things
Click to expand...

Personally I wouldn't risk breaking a 30year old fan with this idea, and risk sticking a broken fan blade through a $500 radiator.

The lack of roar at start up is pretty telling.

Refreshing the clutch hub is a no lose option. I'd try and find a replacement o-ring before tearing into it.
I refreshed a fan hub for one of my cruisers, but the o-ring didn't like being R&R'd and it lost the silicone oil a few weeks after.
There's a part number for the o-ring floating around mud somewhere
 
Did you disconnect the battery recently?
My 94 losses it’s roar after disconnecting the battery until it goes through a few drive cycles
 
jonheld said:
Engine startup rpm has nothing to do with the fan clutch.
All about ambient temp and coolant temp sensor.
Click to expand...
Interesting. Should I be looking at my temp sensors if my initial cold start rpm’s are lower than usual?

I don’t think my 94 has an ambient temp sensor. I did mess with some coolant hoses the other day. As far as the coolant temp sensor, if it went bad, I would think it should throw a code or something. I’m not opposed to changing it if swapping the fan clutch doesn’t work.
 
Last edited:
Broski said:
Did you disconnect the battery recently?
My 94 losses it’s roar after disconnecting the battery until it goes through a few drive cycles
Click to expand...
No I haven’t done anything with the battery. The last thing I did was replace some coolant hoses near the back firewall that was seeping.
 
HuyFZJ80 said:
Interesting. Should I be looking at my temp sensors if my initial cold start rpm’s are lower than usual?

I don’t think my 94 has an ambient temp sensor. I did mess with some coolant hoses the other day. As far as the coolant temp sensor, if it went bad, I would think it should throw a code or something. I’m not opposed to changing it if swapping the fan clutch doesn’t work.
Click to expand...
Your 94 has ECT sensor. Ur ECU reads that measurements. I used TOYOBD1 and Android app to read what the ECU sees... .

20230127_085552.webp
 
HuyFZJ80 said:
Interesting. Should I be looking at my temp sensors if my initial cold start rpm’s are lower than usual?
Click to expand...
Personally, I wouldn't give this a second thought. My LX450 startup rpm varies based on temp. As long as normal operating temperature idle speed is 650, it all sounds good to me.
 
IIRC the 93 and 94 model FZJ80's got the "black hub" AISIN fan clutch, later models got the Eaton which is less prone to the start up roar. Assuming it's the original fan clutch it's possible that some of the silicone fluid that is required for the clutch to engage has leaked out by now. But then if it still feels like there's significant resistance that seems to indicate there's still fluid inside.

Unless there's been some aftermarket electic fan modification, all original FZJ80 fan clutches are the mechanical viscous type with a bimetal spring on the front ie: as it's exposed to hot air (coming through the radiator) the spring changes shape which in turn opens a valve inside the clutch causing more of the silicone fluid to move from one chamber to the other causing the clutch to lock up ie: no wires to communicate to anything else, no sensors, relays, or motors and no codes.

So it's not ususual for some fan clutches, specifically the FJ80 Aqua green hub FJ80 or FZJ80 black hub, to roar on start up (cold engine and fan clutch) as the fan speed may be the same or close to the pulley speed until the fluid goes back to the "cold" side of the clutch and the roar goes away initially, then as the engine and coolant warm up the fan clutch normally will re-engage causing the fan to turn faster again (blowing harder) and the roar may come back under some conditions ie: engine/coolant temps rising significantly.

All that was discussed many years ago by Landtank, Tools-R-Us (happy trails), jonheld, and others.

Here's a link to a long thread started by @landtank who's rebuilt/modified many of these fan clutches:

landtank

Thread 'Blue fan clutch mod...Thread has gone to hell, read at your own risk'

History: On my first drive this summer after replacing my transmission I was having an overheat condition with the truck. On the following weekend while towing a camper it was real severe in the 230* range. After returning I was able to confirm that my Blue hubbed fan clutch was to blame.

This outlines how I adjusted the timing on my clutch.

warning:none of the parts within the clutch are serviceable by TOYOTA. Be gentle with that O-Ring. If it appears to have stretched and there is a bubble when placed in the groove, simply start from the side opposite the bubble and work it...
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Last edited:
Kernal said:
IIRC the 93 and 94 model FZJ80's got the "black hub" AISIN fan clutch, later models got the Eaton which is less prone to the start up roar. Assuming it's the original fan clutch it's possible that some of the silicone fluid that is required for the clutch to engage has leaked out by now. But then if it still feels like there's significant resistance that seems to indicate there's still fluid inside.

Unless there's been some aftermarket electic fan modification, all original FZJ80 fan clutches are the mechanical viscous type with a bimetal spring on the front ie: as it's exposed to hot air (coming through the radiator) the spring changes shape which in turn opens a valve inside the clutch causing more of the silicone fluid to move from one chamber to the other causing the clutch to lock up ie: no wires to communicate to anything else, no sensors, relays, or motors and no codes.

So it's not ususual for some fan clutches, specifically the FJ80 Agua green hub FJ80 or FZJ80 black hub, to roar on start up (cold engine and fan clutch) as the fan speed may be the same or close to the pulley speed until the fluid goes back to the "cold" side of the clutch and the roar goes away initially, then as the engine and coolant warm up the fan clutch normally will re-engage causing the fan to turn faster again (blowing harder) and the roar may come back under some conditions ie: engine/coolant temps rising significantly.

All that was discussed many years ago by Landtank, Tools-R-Us (happy trails), jonheld, and others.

Here's a link to a long thread started by @landtank who's rebuilt/modified many of these fan clutches:

landtank

Thread 'Blue fan clutch mod...Thread has gone to hell, read at your own risk'

History: On my first drive this summer after replacing my transmission I was having an overheat condition with the truck. On the following weekend while towing a camper it was real severe in the 230* range. After returning I was able to confirm that my Blue hubbed fan clutch was to blame.

This outlines how I adjusted the timing on my clutch.

warning:none of the parts within the clutch are serviceable by TOYOTA. Be gentle with that O-Ring. If it appears to have stretched and there is a bubble when placed in the groove, simply start from the side opposite the bubble and work it...
  • Like
  • Love
Click to expand...
Appreciate the info. It appears I’m in for 50+ pages of blue hub goodness.
 
jonheld said:
Personally, I wouldn't give this a second thought. My LX450 startup rpm varies based on temp. As long as normal operating temperature idle speed is 650, it all sounds good to me.
Click to expand...
Well, placed a newly modded blue fan clutch in, and still no roar. Cold start rpms only go a bit higher than 1000, then will lower to 650 when fully warm. Truck runs great otherwise, and the new fan clutch really moves some air! I dunno what else to check except the ECT. Guess I’ll have to try and source a TOYOBD1. Anyone with any suggestions on what I can check?
 
HuyFZJ80 said:
Well, placed a newly modded blue fan clutch in, and still no roar. Cold start rpms only go a bit higher than 1000, then will lower to 650 when fully warm. Truck runs great otherwise, and the new fan clutch really moves some air! I dunno what else to check except the ECT. Guess I’ll have to try and source a TOYOBD1. Anyone with any suggestions on what I can check?
Click to expand...
I don't understand why you are so concerned with startup rpms. They will vary based on temperature. Higher in the winter, lower in the summer. Although I don't think I've ever seen 1800 rpm at startup.
From what you've posted, your truck is running normally.
 
HuyFZJ80 said:
My truck lost its start up roar. Makes me wonder what is wrong.
Click to expand...
What you should be concerned with is coolant temperature. As long as the coolant system is working correctly and the engine temperature remains within specifications, there's not much else to worry about.
What happens at cold startup is irrelevant.

The thermostat starts to open around 180F and is fully open at 203F (82C-95C).
What are your temperatures while driving in various conditions?
 
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