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Thread: Fan Fail light blinking - only at highway speeds

  1. #1
    My friends think I'm nuts jawn101's Avatar
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    Fan Fail light blinking - only at highway speeds

    This is so bizarre. I haven't been able to figure it out.

    I have Dave McKeen's fan fail box (the blue unit) installed, along with Hervey's low-current fans. Fans work great, come on and off as they should. The fan fail unit also works properly - if I run the fans with the car idling and unplug one or both fans, the dash light blinks with one or two flashes exactly as it should. And around town, the light is always off - just as you'd expect.

    But, when I get on the highway - the light blinks double as if it detects both fans being failed, any time that they're on. It doesn't do it unless the fans are running, and the fans are definitely still running even when it's blinking.

    I had thought it might be something with engine RPM (alternator outputting different voltage or something, perhaps?) so I did a test with the car parked and the revs held high - no flashes. Only at actual highway speeds.

    The only (far-fetched) idea I can come up with is that the forward air pressure on the fans is causing them to draw much less current when spinning and the fan fail unit thinks there's no load? Like I said, it's far-fetched.

    Anyone have ideas?
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
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  2. #2
    Senior Member DMC5180's Avatar
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    Have you contacted Dave directly? PM?
    DENNIS

    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  3. #3
    Senior Member Bitsyncmaster's Avatar
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    You could be right that maybe it's detecting low current because the forward air speed. Do you have my fused fan fail or the electronic fused unit? I will have to do a current check of the fans in my car at highway speeds. But I had Hervey fans with the fused fan fail and never saw blinking at highway speeds. I now have Toby's fans.

    Is there a certain speed you see it happen? Are you using my circuit breaker bypass? What voltage do your normally have at high speeds? Low voltage to the fans would mean less current.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
    My friends think I'm nuts jawn101's Avatar
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    Hey guys. Yeah, Dave you and I traded emails about this a few months ago and I didnít want to keep bothering you directly with it! Your suggestion was that I increase the differential threshold on the unit, which I did - all the way up to 20%. My voltage at highway speeds is (if the dash gauge is to be trusted - Iíve verified at idle that itís pretty darn close) right around 13-13.5

    Itís the older fused unit, with 20a micro fuses installed. And I seem to see it at speeds around 60MPH and up.
    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. #5
    Senior Member Bitsyncmaster's Avatar
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    I'm guessing you don't have a clamp on current meter to measure the fan currents. When I had the Hervey fans they would draw 7 to 8 amps each with the engine running. But since your getting the double flash, that tells me it's both fans so I'm guessing the current is to low. If you want to try my new electronic fused fan fail, let me know but I think I set the low current at 4 amps on both units.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  6. #6
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    I'm guessing you don't have a clamp on current meter to measure the fan currents. When I had the Hervey fans they would draw 7 to 8 amps each with the engine running. But since your getting the double flash, that tells me it's both fans so I'm guessing the current is to low. If you want to try my new electronic fused fan fail, let me know but I think I set the low current at 4 amps on both units.
    Hey Dave - no, I donít have a clamp on meter. Maybe I can borrow one somewhere but Iím not sure. Is there any other difference between the electronic and fused units that could fix this? If the current detection threshold is the same I donít know how it would change anything. But Iím not the expert here - thatís asking!
    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

  7. #7
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by jawn101 View Post
    Hey Dave - no, I donít have a clamp on meter. Maybe I can borrow one somewhere but Iím not sure. Is there any other difference between the electronic and fused units that could fix this? If the current detection threshold is the same I donít know how it would change anything. But Iím not the expert here - thatís asking!
    The two units use a different circuit to measure the current but your correct the design should have the same results if the problem is indeed current is to low. Now the question is are the fan currents really below 4 amps each when your driving and if so why. Getting the same result with my other fan fail would verify the fans probably are below 4 amps each.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  8. #8
    My friends think I'm nuts jawn101's Avatar
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    Iím open to try anything!
    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

  9. #9
    Senior Member Bitsyncmaster's Avatar
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    I just ran my car with fan fail jumpers and my otterstat jumpered. I had my clamp on current meter measuring the total fan currents. I have Toby fans and also have the Hervey rubber fan shield (to deflect hot air down to the ground). My alternator pretty much keeps 14.6 volts.

    The cold start in the garage the fan current start at 20 amps and pretty quickly drop as the fan motors heat up to about 18 amps.

    At 60 MPH the fan currents are 16.6 amps.
    At 0 MPH the fan currents are 16.5 amps.
    When I shut the engine off (my fans run an additional 20 seconds) the fan currents are 13.4 amps.

    So I'm surprized the fan currents don't change much with the cars speed.

    PM me your address and I will send you a loner fan fail unit just to make sure it's not something failed in the unit.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
    Senior Member vwdmc16's Avatar
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    Quote Originally Posted by jawn101 View Post
    Iím open to try anything!

    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.

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