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Thread: Replacing flex fan with thermo fan

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    Default Replacing flex fan with thermo fan

    I'm about to replace the flex fan currently installed on my V8 which has a custom-built aluminium radiator based on HQ dimensions (61.5 x 36.5cm core).

    I can't decide whether to fit one large thermo fan or two smaller ones. I have found a 14" fan from AeroFlow that flows 2000cfm.

    And then there is the control unit. The simpler the better, such as the 2-wire senders for oil coolers, but haven't found one for radiators yet.

    Any advice welcome.

    Cheers, pb



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    Don,t do it!! Thermo fans are disaster! Everytime engines are stopped cyl hd/coolant temp rises 15' , so when restart fans come on pulling high amps, may stop engstarting! Had car in past, fitted thermo fan , fan belt would fail after short time due to no cooling air from re moved fan! As to supposed better economy, forget it! Flex fans are as good as you will get!

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    If you do persevere with this, make sure you have a cowling fitted, or made up, to help the fan pull air through the whole radiator rather than just the area covered by the blades.

    Back when I had more of an interest in automobiles, I removed the factory fan from my VN V8 and managed to get the twin thermo setup from the VT V8s into it, and sat across most of the radiator.

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    Stick with the flex fan for the V8, you want air flow all the time to keep the temp down.
    Cheers, Tiny
    "You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
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    My problem is overheating when idling at the lights etc - summer being the worst time, and I live in FNQ.

    When I had the radiator built, I lent the dude a new shroud I bought from a Holden dealer and he went and cut it in half and 'lost' the top half. My car is not a Holden btw.

    I installed the bottom half, but it just doesn't cut the mustard. So I have the choice of getting one fabricated to suit the flex fan - or a thermo fan.

    Tom Mix has a valid point with re-starting a hot motor, and the current drawn by the fan (approx. 10 amps), but that can be overcome with an override switch, that kills the whole fan set-up while starting.

    At night, I always turn my headlights off for maximum battery current before starting because I have a high compression motor. I also have a high capacity AGM battery.

    By the way, I have always used Hawker Odyssey AGM's over the years for the V8. Some people swear by Optima AGM's, so I would like to hear your experiences if you use this type of battery.

    pb

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    any space to mount the thermo fans in front of the rad? to act as "pushers" , then leave the flexi in place?

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    Quote Originally Posted by peteblundoon View Post
    My problem is overheating when idling at the lights etc - summer being the worst time, and I live in FNQ.

    When I had the radiator built, I lent the dude a new shroud I bought from a Holden dealer and he went and cut it in half and 'lost' the top half. My car is not a Holden btw.

    I installed the bottom half, but it just doesn't cut the mustard. So I have the choice of getting one fabricated to suit the flex fan - or a thermo fan.

    ...................
    pb
    The lack of a full shroud is your problem.
    I tried running no shroud with the flexi fan closer to radiator on my old 327 & it got too hot too quickly.
    Put a full shroud on & it kept the temp below boiling in Sydney traffic no worries.
    Cheers, Tiny
    "You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
    The information is out there; you just have to let it in."

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    If thermo fans are so bad why is it that most cars now have them.

    If you have issues starting the engine with the fans on then a relay to turn off the fans while you have the key on the crank position is easy to wire.


    SS Dave
    Old enough to know better, young enough to do it again and better?

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    If the bloke that built your radiator lost half the shroud then, surely, he should be replacing said shroud. As for flexi fan, I'd be leaving it in situ and using the thernos as a compensator for poor airflow when stationary.
    I'm out of my mind, but feel free to leave a message...

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    Yes many cars have thermos but have been designed to do so. Fitting aftermarket one to car not designed for. Is new ballgame, I found not worth it.

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    Quote Originally Posted by VroomVroom View Post
    any space to mount the thermo fans in front of the rad? to act as "pushers" , then leave the flexi in place?
    Unfortunately not, Vroom - the aircon condenser takes up too much room between radiator and grille. The car was built for road and track, so had to have a/c...
    Last edited by peteblundoon; 18-04-17 at 05:36 PM.

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    Quote Originally Posted by SS Dave View Post
    If thermo fans are so bad why is it that most cars now have them.

    If you have issues starting the engine with the fans on then a relay to turn off the fans while you have the key on the crank position is easy to wire.


    SS Dave
    Good solution SS Dave. I had also forgotten that ignition switches usually cut all power to accessories when in the crank position - that's why your radio goes off temporarily.

    My 'daily driver' Subaru has a fabulous twin thermo set-up, complete with shrouds and never overheats.
    I think thermo fans became popular with small cars with east-west mounted motors, (except early Minis - they had a motor-driven fan).
    Last edited by peteblundoon; 18-04-17 at 05:36 PM.

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    No need for Xtra relay. My KB Laser with thermo has prob restarting when fan is on due to old batt. Simply run wire from thermo switch to a mom switch on dash Conn to earth, use while cranking. Keeps. fan relay on.

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    My Nissan Pintara used to boil at the traffic lights during summer.I installed a switch and relay just next to the ignition switch.It has a thermo fan for the A/C when the a/c compressor is switch on but I installed another one beside it.When the temp goes past half at the traffic lights,I switch the second Thermo fan on(The one I installed) It fixed my problem..

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    Been through this with my Monaro (see avatar). Had a flex fan on it when I bought it (factory 350 chev engine) that didn't fill the shroud properly. Use to heat up in slow moving traffic and at traffic lights in summer. Couldn't work it out until I looked at the gaps from the fan blades to the shroud one day. I picked up a Holden factory clutch air conditioning 7 blade fan and now it doesn't go over half on the gauge. Fan fills the shroud perfectly, and free wheels until it's needed to cool. Fixed my problem.
    You can learn alot using Google, and the search button.....

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