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Hot Rods Electric fan stays on to long when engine shuts off

Discussion in 'The Hokey Ass Message Board' started by bigalturk1, Apr 6, 2021.

  1. bigalturk1
    Joined: Sep 23, 2010
    Posts: 367

    bigalturk1
    Member

    On my 41' Willys (Chevy 350 mild build) the electric fan stays on to long. I had to replace the sending unit last summer (On vacation) when the fan stopped working. The parts man sold me another sensor that bolted to my intake manifold and the fan worked fine except that it stays on to long. I don't know the part number of either the old or new sending unit, anyone know a good part # sender to use so that my fan doesn't stay on to long... It usually runs for 5 minutes after a ride on the Hi-way
    (I run a 180 thermostat).
     
  2. Did the old sensor monitor the radiator temp rather than the engine (intake) temp?
     
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  3. Manual override switch, turn it on when needed. HRP
     
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  4. olscrounger
    Joined: Feb 23, 2008
    Posts: 4,122

    olscrounger
    ALLIANCE MEMBER

    is it fed thru a relay? If so then the 85/86 terminal should only energize the relay with the ign in "on" position
     
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  5. G-son
    Joined: Dec 19, 2012
    Posts: 722

    G-son
    Member
    from Sweden

    Takes a lot of time to cool down the intake when there's no circulation in the cooling system. A temperature sensor at the radiator should react much faster - if you feel you need the fan connected so it can run when the car is off at all.
     
  6. On my rod, the fan temperature sensor is on the ground side of the fan circuit, and fan would run on until cylinder head cooled, after ignition was turned off.
    I put an ignition powered relay in the ground circuit. When ignition turns off, the ground is interuppted, so the fan turns off.
     
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  7. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,356

    Blues4U
    Member
    from So Cal

    I would want an override switch so I could turn the fan off entering a car show. I'd hate to draw everybody's attention to the sound of an electric fan..... But that's just me.
     
  8. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,539

    1971BB427
    Member
    from Oregon

    I simply wired mine through a relay that's powered by the ignition switch. So when I stop it shuts off regardless of temperature, just like a mechanical fan does. If your relay is wired hot all the time it's going to run until it cools down. Just switch it to a keyed source and problem is solved.
    The main power to the fan is still on a constant fused hot, just the relay that pulls it in is switched.
    Don't use an override switch or I guarantee one day you'll look down and see the temp spiked and the switch you forgot to turn back on! Been there!
     
  9. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 252

    Fabulous50's
    Member
    from Maine

    https://www.ebay.com/itm/HPC-Electr...-/322150029516?_trksid=p2349624.m46890.l49286

    This is what I use for controlling electric rad fans. Adjustable and will work with 1 or 2 fans, or a 2 speed fan.

    Edit: I have found electric fan controls/switches to work the best in the lower part of the radiator. That way the fan only comes on when you dont have enough airflow to adequately cool the engine. I use the drain port for the sensor usually.
     
    The Magic Ratchet likes this.
  10. Mike Colemire
    Joined: May 18, 2013
    Posts: 1,366

    Mike Colemire
    Member

    What Vall said. Also agree on the over ride switch, a friend of mine drove for 20 miles before he thought to turn on the fan, lucky it wasn't in town driving.
     
  11. jimmy six
    Joined: Mar 21, 2006
    Posts: 8,527

    jimmy six
    Member

    Can you run a mechanical fan?.
     
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  12. Stan Back
    Joined: Mar 9, 2007
    Posts: 929

    Stan Back
    Member
    from California

    I hated electric fans, but had one on my street roadster. Because of the Enderle injection everything was in the way of running a mechanical one. So I put an electric fan on the back of the radiator and made sure it had an adequate shroud so it worked at all. The trick was, when you see something ahead that's going to slow you down (hot day, heavy traffic, long signal, etc.), switch it on. When you park and things are under control, switch it off.
     
  13. 6sally6
    Joined: Feb 16, 2014
    Posts: 1,403

    6sally6
    Member

    X-2!.....That swat-eye done!
    6sally6
     
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  14. Blues4U
    Joined: Oct 1, 2015
    Posts: 5,356

    Blues4U
    Member
    from So Cal

    If it was highway driving, the fan is likely not needed.
     
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  15. Stan Back
    Joined: Mar 9, 2007
    Posts: 929

    Stan Back
    Member
    from California

    See post #12 . . .
     
  16. Or see post #6. Then you can enjoy the ride and not have to think about turning the fan on and off. Just like a factory ride.
     
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  17. Almostdone
    Joined: Dec 19, 2019
    Posts: 439

    Almostdone
    Member

    Perhaps your old sender and new sender have different resistances across temps and the new one is telling your fan it’s hotter than it really is (or the old one was telling it colder than reality). Does your water temp gauge seem to read the same as it used to? See where this is going?

    Anyway, here is a suggestion: try to find a temp sensor that is meant to go with your particular water temp gauge. That is, Stewart-Warner Wings gauge then get the sender for that gauge, etc. OK, perhaps you have the factory gauge .... if so, get a sender for your car, not the SBC. The sender needs to match the gauge. Still not possible, try an SBC sender with a different part number or manufacturer.

    Sorry, no part number answer for you.

    ‘John
     
  18. It’s a bad idea to have it full time powered without the ignition being on
     
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  19. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,539

    1971BB427
    Member
    from Oregon

    You guys go ahead and control your electric fan manually! Lots of cars have been overheated when the steam began and the owner suddenly remembered he'd forgotten to turn it on! Especially if you're turning it off and on as you change from freeway to city streets.
    I'll keep my adjustable stat control, and never think about when to turn it on or off.
     
  20. Fabulous50's
    Joined: Nov 18, 2017
    Posts: 252

    Fabulous50's
    Member
    from Maine

    Heck I forget my blinker on from time to time.....too much rumble from exhaust music to hear it!

    To me the entire point of electric cooling fans is space saving, having then controlled so that they are only on when needed, and vastly improved cooling when idling.
     
  21. 1971BB427
    Joined: Mar 6, 2010
    Posts: 6,539

    1971BB427
    Member
    from Oregon

    Not just space saving, but also a slight performance increase if the motor isn't having to push the fan blades too. But one more reason to use electric fans is as an auxiliary cooling system if a mechanical wont do it alone. When I built my '39 Chev I set the SBC 350 down low in the frame rails to keep the center of gravity low. But the tall narrow radiator doesn't allow the mechanical fan to center top to bottom on the radiator, so it's basically cooling the lower half at idle, or slow driving.
    It works fine in temps below around 85 degrees, or when cruising at freeway speeds. But if it's hot weather, and I am stuck in traffic my engine temps began to creep up. So I installed an electric pusher in front higher on the radiator, and added a T stat set to come on around 185 degrees. Solved my running hot issues when I'm stuck in traffic in hot weather. It used to run 175-180 all the time, and if stuck in traffic climb up around 220 degrees. Now it never gets over 185, as the fan kicks on and cols it right down if it does.
    [​IMG]
     
    Last edited: Apr 7, 2021
    Fabulous50's likes this.
  22. Stan Back
    Joined: Mar 9, 2007
    Posts: 929

    Stan Back
    Member
    from California

    My solution of anticipating the situation to flick on the electric fan to cool the car down before it was really needed was based on 60 years of driving "hot" rods. I have seldom driven one of my cars very far without checking their simple instruments often along the way. Maybe I don't build and prepare them correctly. Maybe I just don't trust myself. Maybe I'm just happy driving and monitoring them.
     
  23. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 3,174

    2OLD2FAST
    Member
    from illinois

    You obviously have better powers of concentration than some of us , I always have alot on my mind & don't want to have to think about anything more than I have to , I just like to enjoy the ride !
     
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  24. stuart in mn
    Joined: Nov 22, 2007
    Posts: 1,896

    stuart in mn
    Member

    Is five minutes really too long?
     
  25. G-son
    Joined: Dec 19, 2012
    Posts: 722

    G-son
    Member
    from Sweden

    An electric fan can draw anything from under 10A to at least 50A. Won't take many of those five minute runs with a powerful fan to drain a battery enough to cause potential issues. Gets worse on a car with small generator/alternator.
     
  26. gene-koning
    Joined: Oct 28, 2016
    Posts: 2,299

    gene-koning
    Member

    When ever I run an electric fan, the power is run through the ignition switch to the thermostat that runs the fan.
    When I walk away from the car, I don't want the fan to be running, and when I'm driving around, I don't want to have to remember to turn a switch for engine cooling.
    I forget a lot more stuff now then I did when I was younger. Gene
     
  27. My engine driven fans never stay on longer than they should


    Sent from my iPhone using H.A.M.B.
     
  28. Lil32
    Joined: Apr 4, 2012
    Posts: 1,809

    Lil32
    Member

    x 2
     

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