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Thread: Fan Fail light blinking - only at highway speeds

  1. #11
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by vwdmc16 View Post
    Get some cardboard and block off half the radiator Inlet, unless it's a super hot day you should still have plenty of air to keep it cool on the freeway. Just for a quick test they should at least be able to make you confirm or deny air flow is the issue. Another ways you could tape off the back of one fan with masking tape and then go on your freeway test drive. If the warning only blinks once then you know you are confirming your theory.
    I did run a fan current test a long time ago on an OEM fan. Blocking air to the fan increased the current which is why I thought air blowing on the fan would decrease it. But after thinking about it more, the fan speed may just be increasing and still drawing the same power. Another test I can do with and OEM fan is to power it up and use my compressor blow gun to see if the currents change. I have two OEM fans, one is still in the stock shroud bolted to the stock radiator. I used those fans when bench testing my fan fail design.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  2. #12
    My friends think I'm nuts jawn101's Avatar
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    These are cool ideas guys, thanks for the suggestions. I could see if Clint’s test helps prove the theory at all when I get som time this week
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
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  3. #13
    Senior Member hippieman9's Avatar
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    Location:  Haw River, NC

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    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Did you ever figure out what was causing this, because a car I’m working on is experiencing the same thing. I have been in contact with Dave in reference this as well. Thinking the Hervey fans are causing this issue, gonna convert to Toby’s fans.

  4. #14
    My friends think I'm nuts jawn101's Avatar
    Join Date:  May 2011

    Location:  Sacramento-ish

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    Club(s):   (NCDMC) (DCUK)

    Quote Originally Posted by hippieman9 View Post
    Did you ever figure out what was causing this, because a car I’m working on is experiencing the same thing. I have been in contact with Dave in reference this as well. Thinking the Hervey fans are causing this issue, gonna convert to Toby’s fans.
    I never did, no. Does the car you’re working on have the Hervey fans too?
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, April 2012 to present
    restoration log, March 2011 to April 2012
    full and detailed photo restoration log

  5. #15
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

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    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by jawn101 View Post
    I never did, no. Does the car you’re working on have the Hervey fans too?
    Yes it does.

    My personal car has Toby’s fans, Dave’s fan fail relay and Dave’s fan relay, no issues at all.

    Going to jump the otter stat and drive the car on the highway and see if the light comes on. If it doesn’t I’ll bet the “windmill” effect is causing the the light to flash.

  6. #16
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

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    I've been thinking about this problem. My new fused fan fail signals a failure when one or both fans have less than 10 volts (a blown fuse would result in low voltage). My micro runs down to 2 volts. But with a very low voltage (fans generating voltage by windmilling) the fan fail light would be so dim you would not see it. My unit drives the fan fail light with input voltage.

    Since one customer has said the fan fail light is bright, all I can think of is the fan fail socket is not getting a good ground. But why would that only be a problem at high speed?

    I did some testing of windmilling with OEM fans a long time ago and don't remember it generating much voltage.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #17
    My friends think I'm nuts jawn101's Avatar
    Join Date:  May 2011

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    Quote Originally Posted by Bitsyncmaster View Post
    I've been thinking about this problem. My new fused fan fail signals a failure when one or both fans have less than 10 volts (a blown fuse would result in low voltage). My micro runs down to 2 volts. But with a very low voltage (fans generating voltage by windmilling) the fan fail light would be so dim you would not see it. My unit drives the fan fail light with input voltage.

    Since one customer has said the fan fail light is bright, all I can think of is the fan fail socket is not getting a good ground. But why would that only be a problem at high speed?

    I did some testing of windmilling with OEM fans a long time ago and don't remember it generating much voltage.
    And I installed your relay strip ground bus, which didn’t fix the issue - and no other evidence of bad grounds (all of which have been cleaned and super upgraded at this point) anywhere else in the car.

    Quote Originally Posted by hippieman9 View Post
    Yes it does.

    My personal car has Toby’s fans, Dave’s fan fail relay and Dave’s fan relay, no issues at all.

    Going to jump the otter stat and drive the car on the highway and see if the light comes on. If it doesn’t I’ll bet the “windmill” effect is causing the the light to flash.
    I never managed to try Clint’s suggestion to block off the radiator temporarily with some cardboard and see if it still happened - was always too hot where I live and then I just forgot! Maybe give that a try too. It’s a smart test.
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, April 2012 to present
    restoration log, March 2011 to April 2012
    full and detailed photo restoration log

  8. #18
    Senior Member Bitsyncmaster's Avatar
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    What I will do when I get time is to solder a wire to a fuse (only need to do one since both fuses are connected to the input pin. Then I will attach my meter to that wire and go drive at high speed and look at the voltage. I have Toby's fans so that may not help knowing what John's fans produce.

    If you still have the fan breaker, you could measure the voltage there. Of course it is only valid if the fans are now powered to read the windmill voltage.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #19
    Senior Member Bitsyncmaster's Avatar
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    Thanks Ryan for testing the voltage with the Hervey fans. He got 5.75 volts at 80 MPH.

    If you have my AC panel LED board this would not be a problem since it has no light at 5.75 volts on the fan fail light circuit. My board will start to glow (very dim) at 6.75 volts.

    Probably would not see any light also if you have an incandescent bulb in the fan fail location.

    You also would not have a problem if you are using a standard fan relay with that center pin still grounded in the fan relay socket since that shorts the fans when the fan relay is off.

    I will look into a change in the fan fail unit to shut down the warning light until the voltage is above 7 or 8 volts. If the car voltage is that low your engine would probably not run.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #20
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    7,324

    My VIN:    03572

    If you have this problem of fan fail light flashing at high speeds due to fans windmilling, I have a fix I can install in your fused fan fail unit to correct it. You would need to return your fan fail unit to me.

    All new sales will have this fix installed.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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