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Thread: Thermofan over Viscous?

  1. #31
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    I don't think I have one laying around but I will have a look in the shed but...

    The best way to test the capacity needed to equal a viscous setup would be to simply hook the current fan up to an electric motor. I have done it in the past with a different fan hooked up to an old washing machine motor. It could not have been more then a few hundred watts at most but then again the fan was much smaller and most electric motors of the grid run at 3000 rpm max.

    Like I said, I will have a look around in the shed what I can find and see if I can replicate the P38 setup somewhat. It should be easy to measure the drawn power and from there we can make SOME conclusions as to how much air is being pushed (pulled actually). As far as I know the amount of power needed to run a fan is more or less linear to the amount of air displaced, all other things being equal. So, with the same fan shape and size 500 watts from an electric motor should be more or less 500 watts form the engine And yes, there are more efficient fan blade designs and what not but still, if you push X amount of air with fan A and it will cost you Y, pushing the same X amount of air with fan B should also cost you Y and not Z.

    So, keithy, if I can't reproduce it because I do not have the gear mate, I'd recommend you do something like this yourself if at all possible and BE CAREFUL since spinning a fan at such speeds can be lethal so you want that motor to be tied down properly and the fan to be mounted exactly centered. You should then be able to get a rough idea of the amount of air displaced and power needed. Spin one of the thermo's up on a free standing workbench or something as well and compare the power consumption.

    Cheers,
    -P

  2. #32
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    Quote Originally Posted by rick130 View Post
    In an east/west engine layout (front wheel drive) with a rad at the front you have (need) a thermofan.
    The majority of cars on the road are front wheel drive. (Only Subaru and some Audi's are north/south layout)

    Of the RWD platforms, it could be cost, noise efficiency, packaging or a combination?
    You can mount the rad/condenser closer to the engine with a thermofan and have the fan mounted ahead as a forced draft fan?
    One less pulley/belt to package? etc.
    Dunno. Eevo has a point. The last truck I drove, a 17 litre V8 Scania 730, which truly DID get loaded up, had thermo fans only, no VC in sight. Possibly Euro 5 needed that, but it worked. Course, the rad was huge, as was the frontal area, but climbing the Warrambungles with 60+ tonne and 40˚C was a test. Truck never got any warmer than it did empty on the flat. Thermo fans seemed to work.
    ​JayTee

    Nullus Anxietus

    ​Getting involved in discussions is the best way to learn.

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  3. #33
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    Thermo fans are often used to reduce fuel consumption,and load on the engine,or as Rick said,when a vehicle is fitted with an east/west engine.
    The VN/VP commodore with the V6 had a huge electric fan,while the 8 stayed with the VF.

    FWIW,the D4 has a VF with electric override,and using the Gap tool the actual speed to the fan can be monitored,and recorded.

    Both the Puma and the TD5 ran the same, well sized VF,that worked well,with a well sized cooling system.
    The VF on these vehicles can often be heard cycling while driving slowly in hot weather.
    The thermo fan on the front of the rad on the TD5 was used for the AC system,or when the engine was overheating.
    Paul

    D2,D2,D2a,D4,'09 Defender 110(sons), all moved on.

    '56 S1,been in the family since...'56
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  4. #34
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    Quote Originally Posted by scarry View Post
    FWIW,the D4 has a VF with electric override,and using the Gap tool the actual speed to the fan can be monitored,and recorded.
    They started with the electro-viscous fan from D3 already, here's from

    WSM-4479 - Workshop Manual - LR3 (L319) - 2005-2009MY

    ....................
    "For additional airflow through the radiator matrix, particularly when the vehicle is stationary, there is an engine driven electro-viscous fan unit fitted to the rear of the radiator. The fan is used for engine cooling and for Air Conditioning (A/C) system cooling. This unit functions as a normal viscous fan, but with electronic control over the level engagement of the clutch. The Engine Control Module (ECM), which determines the required fan speed, controls the level of clutch engagement. The ECM determines engagement based on the coolant, charge air, ambient and transmission oil temperatures and the A/C pressure. The fan is mounted using a left hand thread.
    The viscous fan unit is electronically controlled by the ECM to optimise fan speed for all operating conditions."
    Discovery Td5 (2000), manual, tuned

  5. #35
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    Well, buggered if I can find the bloody thing.

    So unfortunately I can't do this little experiment since I seem to have misplaced my spare fan blade, or I gave it away but I can't remember. Would still be an interesting experiment though. If anyone does get around to doing this, let me know

    Cheers,
    -P

  6. #36
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    Here we go then, it's only been a (f-ed up covid) year

    So I was mucking about and was reminded of this experiment and thought, what the hey... Not going anywhere with all these restrictions and taking the fan out of the P38 is an easy job.
    I have done some testing and although it is by far not conclusive, I have enough data (I think) that I can make some fair assumptions or extrapolate.

    First; the setup. I took a very old AEG drill which was handed down to me from my dad which has two settings, low and high and it also has variable rpm. Low goes up to 750rpm, high is no longer readable on the label but I reckon it would go up to the 3Krpm-ish. The drill is rated at 900 watts. Being an old drill it does not have that newfangled quick stop crap that would break due to the mass of the fan still spinning (I tried it on my makita wireless and it rattled a LOT in protest). With this drill came a circular saw and a wood turning lathe frame/setup. I used the holder for the wood turning lathe frame to hold the drill firmly on a very sturdy and heave steel base (my hoist to be exact) and took an old water pump and pulled the pump propeller. I stuck the resulting axle stub in my drill bit and fixed the pump housing so it would not spin. Finally I fixed the fan onto the threaded end, just as it sits in the car.

    After some low powered test runs and a bit of tweaking I mustered up the confidence to give it full throttle and after a few scary seconds I came to the realization that my drill was not spinning at top speed, by far...
    Now, I lack a tachometer so I can't be sure what kind of RPM I was getting on the drill or the fan for that matter but visually it seemed to me there was minimal slip in the VC (none) at this stage. I switched down gears into first on the drill and gave it the boot (the thumb) and without issue the drill started making the oh so familiar whine it makes at top speed.

    Having done a few test runs, I reckon the drill topped out at around 1500rpm, maybe 2000 in second gear. If I can find a cheap tachometer I'll give that a go some day. I also placed an ammeter in line with the drill and although I forgot to take a no load reading, we'll just assume it's not a lot.

    I registered 1.65A at 230volts on the low setting, spinning at 750RPM. This is close to idle rpm of the engine. If I convert that to watts I end up at 380 watts. That's more than most 12V fans pull btw...
    Switching to high gear on the drill and give it all she had (not too long before the drill burns out) and waiting for the inrush current of getting up to speed settled I ended up measuring 6.6A at 230 volts which is 1518 watts. Like I said, judging by the sound the fan blade made and the sound the drill made from my experience it is between 1500 and 2000 rpm.

    In short, or the TL;DR

    750RPM (idle) takes 380watts from the wall
    2000RPM maximum guessed (100kph on the highway or thereabouts) takes 1500+ watts from the wall

    Some things to take into consideration:
    • The drill losses have not been measured but can't be that much.
    • The losses you get from the bearings and seals in the water pump are added to this measurement
    • slip of the VC is unknown but probably close to zero at this low rpm
    • the cowling and radiators and such were not present, these would cause drag and thus higher power requirements


    When I think about it I do realize that the fan and cowling on a p38 is not really a high tech design and is not the most efficient you can get. A modern, well designed electric fan runs at much lower speeds and thus can use much smaller tolerances since the blades will not deform as much or at all. By that same token, the cowling can be made to fit a lot tighter around the blades causing less loss and higher efficiency. In any case, this is a reasonably fair measurement of power used by a fan I should think.

    Regarding electric fans and their potentially more efficient design, my thinking is this:

    Air is pushed by the blades no matter the setup. Pushing this air takes energy. A free standing fan blade (like in my test) will push a lot of air in your direction but it will also loose a lot of air immediately to the side of the blades which gets sucked right back into the blades and the story continues. Air has still been pushed, energy has been expended. A fan that loses a lot less air due to better cowling and tolerances can have the same amount of air pulled through the radiator whilst expanding less energy to do so.

    My conclusion is; yes electric fans with less wattage can probably do the job but it would have to be one large unit with quite a bit of power. The power used by the VC fan is... a lot Electric fans with a more efficient design will still need a lot more power to come close to the same amount of CFM pulled through the radiator.

    Hope this helps anyone!

    Cheers,
    -P

  7. #37
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    A follow up.

    I got myself a tachometer and ran the tests again so I have some more info to share.

    First of, I did a test run without the fan attached to the water pump assembly to figure out how much power the drill and pump assembly use. To my surprise a perfectly round 1amp at setting 1 and a whopping 1.6amp at setting two. More than I had anticipated.

    Also the dry run has shown the drill to be able to get up to 900RPM on setting 1 and 2900 RPM on setting 2 (as measured on the water pump pulley)

    With the fan attached it was a bit harder to get a proper reading (since holding my fingers that close to a fast spinning fan is a bit unnerving...) but it ended up being 900RPM on the pulley and near as makes no difference the same on the fan at setting 1. Setting 2 gave me almost 1700RPM on the pulley and 1500-1600 on the fan. The readings fluctuated a bit around those figures and like I said, keeping my hand that close to the fan did not give me a lot of time to get an accurate steady reading so make that a plus minus 100 RPM variability each way and it COULD be that they are just the same.

    In conclusion:

    • The slip on the VC is minimal at low RPM
    • the slip on the VC MIGHT be higher at higher RPM but I can not be certain.
    • the maximum speed I got the fan to spin was nearly 1600 RPM
    • power usage at that speed was 6.6 - 1.6 Amps (which is a nice round 5 Amps) at 230v makes 1150 Watts
    • power usage at 900 RPM was 1.65 - 1 Amps = 0.65 Amps at 230v makes 150 Watts


    My VC runs fairly lightly (when compared to a new one I have laying around as spare) when I move it by hand but it does seem that the slip is still fairly limited under load. I do not care to exchange the two for testing as I think we got the figure we were looking for, at least for starters. The electric motor in my drill is most likely not linear in power consumption, certainly when we push it over it's boundaries and I am not sure about the linearity of a fan in power consumption? but it looks like the stock fan does indeed do more poorly when idling or there about compared to a thermofan but starts to pick up very soon since it already surpasses most if not all thermofans at roughly 1500RPM and up in terms of power consumed and I am assuming with that air moving capacity.

    As a final afterthought (for the day anyway) I am wondering if the fan was ever designed to work at 5Krpm. Sure, it has to be able to handle it since it can not explode whilst doing that but practically no one runs their engine at that kinda revs for any kind of time I should think. In other words, the cooling system, in my opinion, was surely designed to work best at the most common revs and engine load which I should think is pulling a heavy load on a steep incline which in most cases would case the gearbox to shift down anyway, say third gear 3.5Krpm. That has been my experience anyway.

    If you are still reading up on this topic Keithy, perhaps you can shed a light on the test you did regarding pulling a load up hill?

    In any case, it would seem to me that at say 3000-3500 RPM the power needed to move the VC fan would be around the 3-4KW range which equates to 4-6HP all very roughly. Now, I am not sure the full amount of power is needed at that point since I do not live down under with massive heat and pulling such loads but, what we do know is that at the bottom end RPM range the fan is JUST enough, barely. Perhaps that was it's minimum design spec and the rest is overkill, ie. you could get away with obviously more thermofan power than you currently have since it has proven to be insufficient but certainly not need the full 4KW for instance.

    Ah well, interested in what the brain trust has for more insights

    Cheers!
    -P

  8. #38
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    Here is an article on the new Toyota 300 series petrol V6.
    Please note the Viscous fan sitting on the front.
    It seems Toyota build their engines conservatively .
    What the New Land Cruiser's Engine Tells Us About the Next-Gen Toyota Tundra (thedrive.com)

    Regards PhilipA
    BTW the Google specific AULRO search engine did not pick up this thread. I wonder why. I found it by chance in technical Chatter when I was going to post a new thread among the half dozen or so existing threads that petered out over time.

  9. #39
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    And the torque curves for both new engines, compared with the outgoing model.

    Gee,we are way off topic now.....


    Paul

    D2,D2,D2a,D4,'09 Defender 110(sons), all moved on.

    '56 S1,been in the family since...'56
    Comes out of hibernation every few months for a run

  10. #40
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    Quote Originally Posted by prelude View Post
    A follow up.

    I got myself a tachometer and ran the tests again so I have some more info to share.

    First of, I did a test run without the fan attached to the water pump assembly to figure out how much power the drill and pump assembly use. To my surprise a perfectly round 1amp at setting 1 and a whopping 1.6amp at setting two. More than I had anticipated.

    Also the dry run has shown the drill to be able to get up to 900RPM on setting 1 and 2900 RPM on setting 2 (as measured on the water pump pulley)

    With the fan attached it was a bit harder to get a proper reading (since holding my fingers that close to a fast spinning fan is a bit unnerving...) but it ended up being 900RPM on the pulley and near as makes no difference the same on the fan at setting 1. Setting 2 gave me almost 1700RPM on the pulley and 1500-1600 on the fan. The readings fluctuated a bit around those figures and like I said, keeping my hand that close to the fan did not give me a lot of time to get an accurate steady reading so make that a plus minus 100 RPM variability each way and it COULD be that they are just the same.

    In conclusion:

    • The slip on the VC is minimal at low RPM
    • the slip on the VC MIGHT be higher at higher RPM but I can not be certain.
    • the maximum speed I got the fan to spin was nearly 1600 RPM
    • power usage at that speed was 6.6 - 1.6 Amps (which is a nice round 5 Amps) at 230v makes 1150 Watts
    • power usage at 900 RPM was 1.65 - 1 Amps = 0.65 Amps at 230v makes 150 Watts


    My VC runs fairly lightly (when compared to a new one I have laying around as spare) when I move it by hand but it does seem that the slip is still fairly limited under load. I do not care to exchange the two for testing as I think we got the figure we were looking for, at least for starters. The electric motor in my drill is most likely not linear in power consumption, certainly when we push it over it's boundaries and I am not sure about the linearity of a fan in power consumption? but it looks like the stock fan does indeed do more poorly when idling or there about compared to a thermofan but starts to pick up very soon since it already surpasses most if not all thermofans at roughly 1500RPM and up in terms of power consumed and I am assuming with that air moving capacity.

    As a final afterthought (for the day anyway) I am wondering if the fan was ever designed to work at 5Krpm. Sure, it has to be able to handle it since it can not explode whilst doing that but practically no one runs their engine at that kinda revs for any kind of time I should think. In other words, the cooling system, in my opinion, was surely designed to work best at the most common revs and engine load which I should think is pulling a heavy load on a steep incline which in most cases would case the gearbox to shift down anyway, say third gear 3.5Krpm. That has been my experience anyway.

    If you are still reading up on this topic Keithy, perhaps you can shed a light on the test you did regarding pulling a load up hill?

    In any case, it would seem to me that at say 3000-3500 RPM the power needed to move the VC fan would be around the 3-4KW range which equates to 4-6HP all very roughly. Now, I am not sure the full amount of power is needed at that point since I do not live down under with massive heat and pulling such loads but, what we do know is that at the bottom end RPM range the fan is JUST enough, barely. Perhaps that was it's minimum design spec and the rest is overkill, ie. you could get away with obviously more thermofan power than you currently have since it has proven to be insufficient but certainly not need the full 4KW for instance.

    Ah well, interested in what the brain trust has for more insights

    Cheers!
    -P
    Hi,

    This topic has been so done to death....................

    There are cars in Oz that just happen to have twin elec engine cooling thermo fans in a shroud that is a very close fit to the rear of a RRC radiator.

    My POS has one of these and has had for a very long time cooling a tired 350 Chev (on LPG) with a stock RRC rad even in stop start traffic in 40 degree heat.

    I've had no need to upgrade the massive 55 amp alternator to run this system. I'm even too lazy to refine it further so one fan is still on all the time the ignition is on, the other fan is on a temp switch.

    You should import these fans and shrouds. You also gain about 100mm of free space in front of the motor.

    DL

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