Viscous vs electric fan





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  1. #1
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    Default Viscous vs electric fan

    Currently my bakkie has a viscous fan and I have been toying with the idea of changing to an electric.

    Mainly because I think it would help the motor turn alittle easier.


    Am I being stupid? Is this something that could help overall? Anyone done this before?

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    Default Re: Viscous vs electric fan

    I had one on a Hardboby with VG30 V6.

    It did not work in slow hard work ! (e.g. Low range in sand)

    On the open easy road without load it works fine. Just don't get stuck behind a slow moving big truck on an incline.

    I will not do the electric fan again.

    .

    If you want to go that route, install the best most effective (read expensive) fan you can fit - with a proper cowling.

    .
    Kobus

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    Default Re: Viscous vs electric fan

    Quote Originally Posted by MartinBravo View Post
    Currently my bakkie has a viscous fan and I have been toying with the idea of changing to an electric.

    Mainly because I think it would help the motor turn alittle easier.


    Am I being stupid? Is this something that could help overall? Anyone done this before?
    I don't quite understand? Do you reason the fan has a lot of resistance on the motor?
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    Default Re: Viscous vs electric fan

    Years back I looked for an electric fan which moved as much air as the viscous unit I had on my tdi. I could not find one. One from a VW came close, but drew huge amps. At that time I did not have access to more modern fans, like in later 4x4s

    Even if you find one, the engine ultimately will still provide the same energy to turn the electric fan when compared to the viscous fan, ignoring inefficiencies of creating electrical energy and then converting it back to moving air. The only advantage is that the battery will supplement some energy when the fan is on, not drawing all power from the engine, like with a viscous fan when it locks up. But then the battery will have to recharged when the electric fan is off, still drawing some power from the engine.

    I would stick with the viscous fan, which was designed for the vehicle


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    Default Re: Viscous vs electric fan

    A viscous fan draws 7kw off the engine. I removed viscous and fitted electric fans to 2 of my vehicles with success. a 2.5 XJ Jeep and a 2.8 Isuzu fitted with a 3.1 import motor. You should gain in the region of 2 km/l. the most important thing is to make sure that the cowling seals properly. Fit a thermal switch in the top hose of the radiator to switch on at 92 degrees and off at 82. Never had any problems working under load or slow work. Most of the vehicles with transverse engines have electric fans.
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    Default Re: Viscous vs electric fan

    With our race cars over the years we have used electric fans with a on / off switch. The fan was switched on for the out lap and switched off on the grid before the start of the race. On the slow down lap you switched the fan back on. The reasoning behind this was that over 30 km/h the fan has very little to no influence on the airflow over the radiator. As mentioned in other posts the electric fan doesn't draw power directly from the motor. In a 4x4 environment where I was modifying the system, I'd fit an electric fan that is correctly ducted. The thermal switch to activate the fan should switch on at a lower temperature than normal, I'd say 80°c. Make sure that the fan can move the correct amount of air over the radiator during prolonged slow driving.
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    Default Re: Viscous vs electric fan

    Quote Originally Posted by Pieterk View Post
    A viscous fan draws 7kw off the engine. I removed viscous and fitted electric fans to 2 of my vehicles with success. a 2.5 XJ Jeep and a 2.8 Isuzu fitted with a 3.1 import motor. You should gain in the region of 2 km/l. the most important thing is to make sure that the cowling seals properly. Fit a thermal switch in the top hose of the radiator to switch on at 92 degrees and off at 82. Never had any problems working under load or slow work. Most of the vehicles with transverse engines have electric fans.
    Which fans did you use? Are generic off-the-shelf fans still as useless as they were 10 years ago?

    Yip, the viscous fans use a lot of power when engaged, but they move large volumes of air. And the quoted 7kW of power will be at full revs. Like Paul says, during normal driving speeds the natural airflow is enough for cooling and no fan assistance is needed, unless your front opening is restricted. The viscous fan here idles along and hardly uses any power.


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    Default Re: Viscous vs electric fan

    Personally, I have a lot of faith in a viscous fan.

    Under normal open road travelling, that fan is not engaged. Thus it won't be a drain on power.

    Under load both the electric as well as the viscous fan need to cool the coolant by the same margin. Thus the energy drain on the motor should be the same, or very very close.

    So, will you gain by fitting an electric fan? Not if the fan is the right spec electric fan. I ran 2 x RunX fans on my 80 and their start up current was 32A. Running current was 16A. Any other electric fans were just a waste of time.
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    Default Re: Viscous vs electric fan

    Quote Originally Posted by Tweeling View Post
    I don't quite understand? Do you reason the fan has a lot of resistance on the motor?
    Surely the fan turning will provide some resistance to the motor,
    Not alot, but some


    after reading the posts here, I figure its not worth converting. not for up to 7kw

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    Default Re: Viscous vs electric fan

    I did a trip Gaborone - Pta with the fans fitted before I had a thermal switch*. Only a manual switch was fitted. Radiator, thermostat and temp gauge was all in good working condition. From leaving home early (no city traffic) up to Pta I did not have to switch the fan on once. Only once I hit the busy city traffic I had to switch it on every now and then. Like it was mentioned in one of the above posts - over about 40km/h (no heavy load), the airflow over the radiator is enough to keep the temp at normal. In the same way the viscous fan (in good condition) will not put much stress on the engine - most of the time it is just free running.

    Things change rapidly once the engine starts to work harder.

    .

    * I used a VW Kombie thermal switch. It has 2 outputs at different temps. The 2nd fan then only switched on at higher temp.
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    Default Re: Viscous vs electric fan

    Quote Originally Posted by KobusDJ View Post
    I did a trip Gaborone - Pta with the fans fitted before I had a thermal switch*. Only a manual switch was fitted. Radiator, thermostat and temp gauge was all in good working condition. From leaving home early (no city traffic) up to Pta I did not have to switch the fan on once. Only once I hit the busy city traffic I had to switch it on every now and then. Like it was mentioned in one of the above posts - over about 40km/h (no heavy load), the airflow over the radiator is enough to keep the temp at normal. In the same way the viscous fan (in good condition) will not put much stress on the engine - most of the time it is just free running.

    Things change rapidly once the engine starts to work harder.

    .

    * I used a VW Kombie thermal switch. It has 2 outputs at different temps. The 2nd fan then only switched on at higher temp.
    Sorry Kobus but you are not taking certain things into account

    First off what fan did you fit? Was that fan's airflow rating high enough to meet or exceed your Viscous fan's airflow?

    Proper electric fans can engage slow rotations at lower temperature and then ramp it up as the temperature increases and is not effected in the same way by the engine RPM
    Which means they can ramp up the cooling while your engine is running at 1000 or 2000rpm
    And you can look at dual electric fan setup where you fit 2 electric fans (which allot of cars do these days in any case)
    most of these can also have their fan direction changed so you can technically fit one in front of the radiator if needed

    This would insure your temps is kept in place

    So if you were getting temp increases at low speed when using the electric fan on your car then it is most likely that unit was not able to meet the vehicle requirements but it does not mean "electric fans" as an whole is unable to do so

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    Default Re: Viscous vs electric fan

    Quote Originally Posted by Veneficus View Post
    Sorry Kobus but you are not taking certain things into account

    First off what fan did you fit? Was that fan's airflow rating high enough to meet or exceed your Viscous fan's airflow?
    I did this back in 2005/2006. I could only fit what was available locally at that time. I must admit that it was not the most effective fans.

    I just relay the experience I had at that time.

    .

    Surely modern fans will be up to the task. (Like I said n my first post)
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    Default Re: Viscous vs electric fan

    This is the one I fitted to my 4.6 V8 automatic 130 defender: Look for part for the 90/110 dedfender.

    https://www.revotec.com/acatalog/Lan...ling-Kits.html

    I also added the manual on/off/auto switch, wish I had made the change earlier, temps never rise and if Im approaching a tough uphill section I turn to manual before the hill

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    Default Re: Viscous vs electric fan

    I bought a Merc Fan/shroud combination and fitted it to a BMW 740 or 540 radiator. Just needed to mount it upside down to clear the bonnet. Paid less than R200 for it. Its an available speed fan that also provide airflow for the Aircon Condenser. Rated at 600Watts at 12.5V. It needs a PWM signal between 10 and 15Hz to operate. Fixed that at 12Hz. Changing the PWM duty between 15% and 90% will vary the speed. At 80% it draws 28 Amps and at 90% it shot up to 51.5 Amp.

    Built a Controller where I can set the RPM, at whatever Temp. It will also control the Condenser airflow when that is fitted. Will finish that project when I am back in SA.

    It is in my Defender 110
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    Default Re: Viscous vs electric fan

    Quote Originally Posted by mikeml View Post
    Which fans did you use? Are generic off-the-shelf fans still as useless as they were 10 years ago?

    Yip, the viscous fans use a lot of power when engaged, but they move large volumes of air. And the quoted 7kW of power will be at full revs. Like Paul says, during normal driving speeds the natural airflow is enough for cooling and no fan assistance is needed, unless your front opening is restricted. The viscous fan here idles along and hardly uses any power.
    I used generic fans, procured from Siverton radiators.
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    Default Re: Viscous vs electric fan

    My touareg had two electric fans as standard. No viscous fans.

    The fans together was around 850 watts iirc.

    Electric fans can save fuel as they are only used when needed.

    But you need a high power fan to cool properly when needed. The generic midas ones may work for a/c condensers but are useless for cooling a hard working engine.

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    Default Re: Viscous vs electric fan

    if ones puts on a electric fan get the biggest you can install, not some Chinese rubbish, also get a full cowl made, mount fan to cowl, i do not like those pull through ties that are used to secure fans, they can vibrate loosen over time and with the weight of fan the ties can damage the radiator cores
    the ones in the pick are twin stage or 2 speed fans,
    advantage of a viscus it blows air all time over engine bay moving the air and water temp is mostly constant, a electric there is always about 5-10 deg flucuation for when fans kick in and kick out


    also fit a thermo switch
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