On the Truck Fan Clutch Analysis

[greentruck]

This was prompted by reading through (again!) Landtank's monumental fan clutch thread and not finding an answer. That was sparked by listening to our truck at idle as I charged a lawnmower battery up. I have a Scangauge, so get accurate digital water temp readouts. Here's what was happening.

The air temp was around 90 degrees. The truck was idling when I heard the fan kick on with the roar you expect. The water temp at that point was 198 F. This continued for a reasonable amount of time until it cut out at 187 F.

I modded and reinstalled my fan clutch about 3 years ago when I installed a new radiator. I forget what weight silicone fluid I used, but remember not putting a complete fill in, so not sure if there's a full 59 ml in it or not. The truck has generally run cool as necessary, but would prefer to bring water temp down about 5F. It generally runs between 190 and 200 F, but will frequently climb above 200 when the AC is on.

Most of the temps in LT's thread refer to taking it off the truck and placing the clutch in a hot water bath and adjustments between 90 and 125 F. I recall fussing over this, but not what settings I ended up with. This seems to have worked for me in getting the clutch operating generally within the nominal temp range.

My experience a few days ago got me wondering about what you can tell from how the clutch acts when still on the truck? I'm talking about something beyond the "grab it and see if the blade stops" sort of thing. Besides being able to check the performance of a clutch you modify and reinstall as I did, are the kick-in/kick-off set points while mounted in the truck's cooling system useful in analyzing fan clutch performance? What do mine say about whether I'm milking as much cool as possible out of the cooling system or should I consider adding some more silicone goop?

 

[greentruck]

Bumping this...any thoughts on this as a way to confirm appropriate fan hub clutch operation?

 

[baldilocks]

Bumping this...any thoughts on this as a way to confirm appropriate fan hub clutch operation?

I have the older black hub clutch on my 1993 and the timing was left stock but I did fill it all the way to the top of hole with 15k, which is the heaviest oil advised for this clutch.

It comes on full roar by 190 and kicks off at 185 according to my Koso digital temp gauge with sender in the outlet pipe. I’ve set my hand throttle to 1400rpm and watched this cycle go on for an hour or more.

Yesterday I ran it to charge the battery since I haven’t been driving it much lately and when the fan began to make noise the gauge was at 189. I find that, after driving and then pulling into the garage, this cycle may be more like 192 on and 187 off for a while.

We did some Rubicon wheeling a couple weeks ago when ambient temps were in the mid 80’s and she would creep all day between 187 and 190-192.

It seems that the blue hub clutches are not as robust and need to be recalibrated once every few years.

 

[mudgudgeon]

I’ve set my hand throttle to 1400rpm and watched this cycle go on for an hour or more.

Better than TV

 

[sunrk]

The fan clutch doesn't 'kick in' on an 80 (or any other toyota diesel with viscous fan clutch). The fan runs all the time, but it's the rate at which it runs that changes in response to 'heat soak' through the metalwork of the engine and radiated back towards the motor at the fan clutch body temperature itself changes. The fan can never run any faster than the motor is running as the pump is belt-driven off the crank pulley, and that's what drives the fan clutch.

The cooling system has four important parts - water pump, radiator, thermostat and fan + clutch (plus shroud).

When the motor is switched off, the fan blades do not turn more or less 'freely' like a totally un-braked ball-bearing type fan (such as a thermofan) will. There should always be some 'resistance' and that should be less at cooler temps.

The thermostat is the most critical part as it controls how/when coolant will be allowed to flow out of the engine and through the radiator. The fan and radiator do absolutely nothing when the motor is cold/cool as there is not yet any coolant flow via the thermostat so there's no waste energy as heat (in the coolant solution) for the radiator to radiate.

You can tell that the cooling system is working as if you drive hard and load the motor with a digital temp gauge of some sort installed, you'll see the temp rise up to about 85 to 90 C or maybe a little higher then with the fan and radiator both doing there job it will drop down. Not sure with the petrol motor, but with the 1hz and 1hdt diesel motors the standard temp is 75 to 78 C.

If the coolant temp is getting up to 95 C or higher for long periods of time the cooling system isn't working properly.

Remember that the cooling system sheds waste energy from combustion. The only beneficial use of heated coolant is to heat the cabin air via the heater core, otherwise all that heat is just waste. So you want the system to be as effective as possible.

Automotive engines do not get hot enough for the waste energy in coolant solution to do any useful work.

 

[inkpot]

On the 1fz glasser the thermostadt let's the cooler coolant from the bottom of the radiator into the motor.

 

[greentruck]

I have the older black hub clutch on my 1993 and the timing was left stock but I did fill it all the way to the top of hole with 15k, which is the heaviest oil advised for this clutch.

It comes on full roar by 190 and kicks off at 185 according to my Koso digital temp gauge with sender in the outlet pipe. I’ve set my hand throttle to 1400rpm and watched this cycle go on for an hour or more.

Yesterday I ran it to charge the battery since I haven’t been driving it much lately and when the fan began to make noise the gauge was at 189. I find that, after driving and then pulling into the garage, this cycle may be more like 192 on and 187 off for a while.

We did some Rubicon wheeling a couple weeks ago when ambient temps were in the mid 80’s and she would creep all day between 187 and 190-192.

It seems that the blue hub clutches are not as robust and need to be recalibrated once every few years.

Thanks for the data points, they're very useful. I didn't really pay any attention to this when I first modded the clutch, but I don't think I've lost any performance. It's just that I think I have more to gain in terms of cooling by having the clutch engage sooner. I suspect my 198 is on the high side, so I'm not getting the benefit of the best draft through the radiator until I get to the higher end of what I have found to be the operating range in regard to water temps. Mine runs 190 to 200, while I'd prefer to be in the 185 to 195 range

I've got a new shroud and fan blade to install in the near future, so will fuss over that fan clutch when that's torn down.

 

[greentruck]

The fan clutch doesn't 'kick in' on an 80 (or any other toyota diesel with viscous fan clutch). The fan runs all the time, but it's the rate at which it runs that changes in response to 'heat soak' through the metalwork of the engine and radiated back towards the motor at the fan clutch body temperature itself changes.
SNIP

The thermostat is the most critical part as it controls how/when coolant will be allowed to flow out of the engine and through the radiator. The fan and radiator do absolutely nothing when the motor is cold/cool as there is not yet any coolant flow via the thermostat so there's no waste energy as heat (in the coolant solution) for the radiator to radiate.

SNIP

Well, yes, it does run all the time. Speaking colloquially here, it's after 5 on Friday.
Let's just say it makes a dramatic entrance when it shows up.
It's that heat soak that I'm trying to temper some by having more fan, earlier. I'll get back with a report when the deed is done and tested.

 

[Bambusiero]

Speaking of heat soak (stored energy) - not exactly addressing anything that's already been said, but throwing in a related aspect I've seen over and over on my truck...

Say, you are running steady state on the highway, medium high engine load, hot day, coolant temperature steady and nominal at 193F.
1) Slow down quickly:
2) Engine load (heat input) drops significantly, but so does coolant pump and fan speed (heat dissipation rate).
3) But, in a few tens of seconds, coolant temperature rises by a few degrees, contrary to what you might expect.
4) It may take a couple of minutes for coolant temperature to settle back down.

From this, it seems that there is significant mass in the engine (probably the head?) already at a higher temperature than the coolant, and with the reduced dissipation rate, coolant temperature increases for a while until the excess heat is shed.

And/or - maybe this means the fan thermostat action is not very responsive?

 

[landtank]

It's that heat soak that I'm trying to temper some by having more fan, earlier.

my point of view is the same. I've never seen a fan not rotating when the engine is running. So the fan is always "on".

There are 2 ways to influence the amount of drive transferred to the fan. 1. the amount of oil being sheared at any given temperature and 2. the CST of the oil used.

Manipulating either of these 2 variables can have an increase on how the clutch responds, how ever changing both in concert can dramatically improve performance over changing just one alone.

By increasing the CST of the oil and adjusting the timing plate to a lower temperature, the drive comes in earlier and stronger due to the higher CST and increases at a greater rate as the temperature increases due to shearing a progressively larger volume of oil. So you have basically not only have increased the cooling at the lower temps but with the increase in the amount of oil being sheared stay ahead future demands.

This is basically the end result of my "blue fan clutch mod" thread. Trying to stay ahead of heat soaking the engine.

 

[Kernal]

Has anyone noticed any change in MPG or Power with a fan clutch that's been modded (engaged more often) than a stock clutch? Seems like
that was discussed years ago, I forget.

 

[greentruck]

SNIP

Manipulating either of these 2 variables can have an increase on how the clutch responds, how ever changing both in concert can dramatically improve performance over changing just one alone.

By increasing the CST of the oil and adjusting the timing plate to a lower temperature, the drive comes in earlier and stronger due to the higher CST and increases at a greater rate as the temperature increases due to shearing a progressively larger volume of oil.
SNIP

This is basically the end result of my "blue fan clutch mod" thread. Trying to stay ahead of heat soaking the engine.

Rick,
Thanks, I know I'm on the right track it seems then, I just need to keep pushing. I think getting the timing to a lower temp and adding higher CST to top it off should put me where I need to be. I was being cautious to not over do either when I last was working on it, I just need to pick up that slack. What I'm aiming for is 192 F (locked up) to 185 F (released) on the fan clutch.

 

[greentruck]

Has anyone noticed any change in MPG or Power with a fan clutch that's been modded (engaged more often) than a stock clutch? Seems like
that was discussed years ago, I forget.

Yeah, it was stewed over and I don't think it was ever resolved. I think it depended on where you started and how far you pushed things. Pushing more air harder is going to take more energy, but if where you started was actually from a point where the fan was already fully locked, you may have seen no difference.

But if you started wide afield and the fan had been doing mostly freewheeling, then getting it to lock up a high % of the time by modding it might make a considerable difference in MPG.

However, there's such a thing as too much cooling, because my understanding is that most cars are designed around being most efficient at a certain temp to optimize fuel mileage and pollution control. It's possible that some of any loss in fuel efficiency might be due to the lower thermal efficiebncy of operating below the nominal design operating temp.

I'm not an engineer so those are all more theoretical than supported by evidence I can put a finger on right now.

 

[Kernal]

Roger that, Mike.

 

[-Spike-]

However, there's such a thing as too much cooling, because my understanding is that most cars are designed around being most efficient at a certain temp to optimize fuel mileage and pollution control. It's possible that some of any loss in fuel efficiency might be due to the lower thermal efficiebncy of operating below the nominal design operating temp.

I'm not an engineer so those are all more theoretical than supported by evidence I can put a finger on right now.

Blow as much air as you want over a 1fz, you won't lower the temp enough to measure, let alone get it below optimal operating temps. The thermostat controls water flow, if you make the water colder the thermostat will just let less of it through, maintaining the designed temp range. There is certainly a point of diminishing returns, where the radiator can't make use of the air flow available, but I'd rather have too much than not enough.

 

[greentruck]

Blow as much air as you want over a 1fz, you won't lower the temp enough to measure, let alone get it below optimal operating temps. The thermostat controls water flow, if you make the water colder the thermostat will just let less of it through, maintaining the designed temp range. There is certainly a point of diminishing returns, where the radiator can't make use of the air flow available, but I'd rather have too much than not enough.

Yeah, that's pretty much where I'm trying to get: As close to the point of vanishing returns as possible without wasting extra fuel doing so. With my fan clutch not fully engaged until 198 F, I think I'm not there yet, i.e. there's more cooling I can get with relatively little cost in fuel.

 

[-Spike-]

Yeah, that's pretty much where I'm trying to get: As close to the point of vanishing returns as possible without wasting extra fuel doing so. With my fan clutch not fully engaged until 198 F, I think I'm not there yet, i.e. there's more cooling I can get with relatively little cost in fuel.

I'd agree with that. I'd think fully engaged at 190 would be good, but whatever @Tools R Us set my clutch at works very well, so I'd defer to his judgement if it differs from that. He told me what he was doing at the time, but I can't remember s***.

I've had good results from filling the gaps on all four sides of the rad with foam, if you haven't done that yet. Adding foam at the top and bottom gave me a dramatic improvement in A/C vent temps.

 

[greentruck]

Yeah, I have foam in there, but it's big-box house type stuff. I'm going to see about an upgrade there. It really does make a difference.

 

[Bambusiero]

I did this with the soft white big-box house weatherstripping type stuff when the radiator was installed.
It is holding up well and doing a good seal job.
No complaints except maybe - it's more of a pink panties sort of sexy than a black macho sexy...

Radiator install:
Glue sealing foam to front 4 edges with contact cement. Stays in place perfectly during install. No hassles.
Put a strip under the side brackets too. There's a gap.
Foam seal used is "md" brand (from Home Depot), 1/2" x 1 3/8" x 42" Premium AIR CONDITIONER WEATHERSEAL.
It's white closed cell foam.
You need 3 packages.

 

[greentruck]

I did this with the soft white big-box house weatherstripping type stuff when the radiator was installed.
SNIP
Foam seal used is "md" brand (from Home Depot), 1/2" x 1 3/8" x 42" Premium AIR CONDITIONER WEATHERSEAL.
It's white closed cell foam.
You need 3 packages.

The main issue with the stuff I used is it's not closed cell. It works, but it could be better. Not going to pull the radiator, but I think I can improve it pretty easily