What contributes to “Roar” at cold start-up?

[Nbndallastx]

I’ve searched the forum and know the clutch fan is the main driver for the “Roar” just wondering if it’s the only driver?

Reason for the question, I installed a blue Aisan hub less than a year old with 20k fluid swap on my ‘93 fzj80. It use to “Roar” however 3months ago it stopped roaring BUT it still pulls tons of air at start up…actually I think it’s pretty much always locked up (wonder if that’s bad😅)

Most important thing is the rig doesn’t over heat even during this past very long hot Texas summer…

Can a hub go out that fast? Why would it stop roaring🦁?

Just want to learn more about this part…thx!

 

[gummycarbs]

I believe that the startup roar is caused by the fluid settling to the bottom.

If you want it to really roar, I guess you could go get it hot on hills in the summer, then park it and leave it until the dead of winter.

It's more important that it flows sufficient air when hot. I know that if I'm in stop and go traffic or a drive-through in the summer months, when I pull out into the road the engine feels relatively gutless and I can hear some fan roar. It takes a lot of energy to spin the fan up with the fan clutch fully engaged.

 

[bubfuji]

With the engine off (cold). Does the fan rotate easily? Or do you feel it drag when rotating by hand?
Is there oil on the fan blades?

With the engine off (hot). See if you can rotate the fan and compare the differences between a hot and cold engine.

There is a viscous coupling and a thermostat lock.
On a cold engine, you can feel the fan turn easy then feel a drag. This is because the viscous fluid settles inside the fan clutch.
On the front of the fan clutch is a thermostat coil that expands and locks the fan to the hub to provide maximum cooling when the air/engine through the radiator is really hot.

 

[jpoole]

Echos of the ancient dinosaurs that compose your gasoline are a key "roar" ingredient. Maybe you've been running too much ethanol in your fuel and the corn silence is damping the dinos down?

I'd plan to do a fluid change and plate timing / temp setup on the clutch personally. It's something that I think should be done on all new clutches and any time you question the performance of the clutch on the truck.

 

[mudgudgeon]

Can a hub go out that fast?

If the oil has been changed, the o ring may not have sealed properly.
I had one lose all it's oil in about 2-3 months because the o-ring didn't seal effectively

 

[OSS]

^ that

 

[nukegoat]

With the engine off (cold). Does the fan rotate easily? Or do you feel it drag when rotating by hand?
Is there oil on the fan blades?

With the engine off (hot). See if you can rotate the fan and compare the differences between a hot and cold engine.

There is a viscous coupling and a thermostat lock.
On a cold engine, you can feel the fan turn easy then feel a drag. This is because the viscous fluid settles inside the fan clutch.
On the front of the fan clutch is a thermostat coil that expands and locks the fan to the hub to provide maximum cooling when the air/engine through the radiator is really hot.

I thought the thermostat thing just dictates how much fluid to allow to pass through, changing viscosity based on temp?

 

[LongDuck]

 

[Nbndallastx]

holidays kept me busy sorry for the delay…

The old Aisin mod fan locked up just fine and was essentially on 24/7…

Just added a brand new Aisin hd blue clutch fan (not modded) and still no ROAR…

I don’t have over heating issue and the Car runs great just weird that it stopped doing it🤔

I did just de-smog the 1fzfe…so took out the Pair/ERG/some hoses but can’t remember if the ROAR stopped before or after🤷🏻‍♂️

anyone know if an old water pump might contribute to this given the clutch spins on that bearing? Or VSV switch contribute some how from sn idle RPM POV?

I use to hold like 1900RPM at start up for 2mins then go back to 650RPM…now it goes to 1200RPM for a second then to 650RPM

Anyways just curious…the rig runs great so not sweating it

 

[Nbndallastx]

Echos of the ancient dinosaurs that compose your gasoline are a key "roar" ingredient. Maybe you've been running too much ethanol in your fuel and the corn silence is damping the dinos down?

I'd plan to do a fluid change and plate timing / temp setup on the clutch personally. It's something that I think should be done on all new clutches and any time you question the performance of the clutch on the truck.

Interesting nugget on the gas 🤔

 

[manofthewoods]

holidays kept me busy sorry for the delay…

The old Aisin mod fan locked up just fine and was essentially on 24/7…

Just added a brand new Aisin hd blue clutch fan (not modded) and still no ROAR…

I don’t have over heating issue and the Car runs great just weird that it stopped doing it🤔

I did just de-smog the 1fzfe…so took out the Pair/ERG/some hoses but can’t remember if the ROAR stopped before or after🤷🏻‍♂️

anyone know if an old water pump might contribute to this given the clutch spins on that bearing? Or VSV switch contribute some how from sn idle RPM POV?

I use to hold like 1900RPM at start up for 2mins then go back to 650RPM…now it goes to 1200RPM for a second then to 650RPM

Anyways just curious…the rig runs great so not sweating it

You can have my "old" water pump that was working fine before my rebuild. Just cost ya shipping.
Guaranteed for 2 million, feet!!!
Seriously, just let me know

 

[Nbndallastx]

You can have my "old" water pump that was working fine before my rebuild. Just cost ya shipping.
Guaranteed for 2 million, feet!!!
Seriously, just let me know

Thx a ton for the offer! Mine is currently working just old…

 

[gummycarbs]

I use to hold like 1900RPM at start up for 2mins then go back to 650RPM…now it goes to 1200RPM for a second then to 650RPM

Neither of those sound right to me, but it varies by outside temperature and whether or not the AC is on. Vacuum leaks and carbon buildup happen slowly over time, so we don't really notice how startup behavior has changed.

If you're only seeing 1200 RPM on a cold startup, that's probably why you don't hear any roar. Off the top of my head, I would say around 1600 is more normal for a cold startup in cold weather with the AC off.

The water pump couldn't cause the fan not to roar. It's just a shaft that spins the fan hub and the impeller at the same rate.

 

[Nbndallastx]

Neither of those sound right to me, but it varies by outside temperature and whether or not the AC is on. Vacuum leaks and carbon buildup happen slowly over time, so we don't really notice how startup behavior has changed.

If you're only seeing 1200 RPM on a cold startup, that's probably why you don't hear any roar. Off the top of my head, I would say around 1600 is more normal for a cold startup in cold weather with the AC off.

The water pump couldn't cause the fan not to roar. It's just a shaft that spins the fan hub and the impeller at the same rate.

Thanks for azimuth check! You’re right about temps changing start ups…had a 75ish day this week and it sounded different…I could hear the motor adjust to find the right idle…I’ll just enjoy these good running days🙌

 

[Sarmajor]

On the front of the fan clutch is a thermostat coil that expands and locks the fan to the hub to provide maximum cooling when the air/engine through the radiator is really hot.

No it doesn’t. The thermo coil drives a valve inside the viscous coupling to vary the amount of oil in the scrolls inside the coupling. The hotter it gets the more oil is allowed to enter the scroll to increase the lockup of the coupling. It is a continuous process as long as the engine is running. When the engine is off the fluid settles to the bottom of the coupling filling the bottom of the scrolls. On startup the fan will roar due to air movement until the oil is pumped back into the rear housing of the coupling.
They are an ingenious piece of kit and mostly work fine although mine had virtually no oil in it after 375,000 km. Refilled it and normal service was restored.

 

[bubfuji]

I agree with your comments.

It does not lock the fan in place when hot. What I should have said ,when the coil gets hot the amount of slip is reduced to produce more cooling.