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    Thread: Radiator Fan issue

    1. Member
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      09-29-2019 07:23 AM #1
      Have a 87 Scirocco 8v.. the radiator fan won't come on when it gets hot. It does run when the A/C is turned on. I put in a new temp sensor and the fuse is fine. It just won't come on however, is there anything else to check? the Bentley didn't identify a relay for it. thanks!

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    3. Member
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      09-29-2019 08:44 AM #2
      Did you verify that the sensor that you removed was bad? Bench test it? I would say that if you confirmed it to have failed, then I believe air in the system could prevent the sensor from reaching that magic closed position temperature. Forgot what that is. Also make sure that the connection is solid at the sensor. Had that issue in the past on a different car. Connection was corroded and nearly lost my car from overheating. Wiring could be damaged as well. Good luck. Jim.


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      09-30-2019 03:25 AM #3
      Did you check the coolant level in the radiator? It has to touch the sensor to turn on the fan.

      The wiring could also be bad to the fan sensor as Jim mentioned.




      As far as it working with the A/C on:

      The fan will always come on if you turn on the A/C unless that is broken also.

      That's probably mentioned in your owner's manual if you have it.

      I think that's common for cars with electric radiator fans and A/C.

      The engine RPM will also increase when you turn on the A/C. That's common to all cars with A/C including my 1977 Ford.

      Using the defroster in the winter turns on the A/C compressor. Also common to cars with A/C including my 42 year old Ford.

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    6. 09-30-2019 11:51 AM #4
      I believe the fan uses a switch which is a lot different than a sensor. Switches are on/off and sensors are a variable signal/resistance.

      So the switch at the lower radiator is pretty simple to check. If you have a wiring diagram, you could just jump the right wires and the fan should come on. You can also check if there is power at the switch. If the fan is not coming on AND it's overheating, then it sounds like it may need a switch.

      One thing that matters is how do you know if the engine is overheating? I would not trust the gauge. I've been burned in the past. If the gauge is reading hotter than it should and the fans do not come on, it might be cause the gauge is reading hotter than it should and the fans are not suppose to be on yet.

      It has been my experience that the fans are pretty good. If they do not work, it's typically the fan switch. By bypassing the switch, you will know if the fans work or not.
      Last edited by Butcher; 09-30-2019 at 11:54 AM.

    7. 09-30-2019 04:07 PM #5
      Just chiming in, Butcher, Jimmey & 53PL* already covered most of what you need to know
      (Yes, that big brass thing screwed into the Radiator is a Thermo-Switch, not so much a Temp Sensor...).

      One of the wires leading to it should have unswitched battery juice, Hot All the Time.
      (Recall how the Fan will sometimes come on all by itself after you've shut the car off, after an esp hot run?)

      Battery, ThermoSwitch, Fan, Chassis Ground makes a complete and independent circuit.
      The A/C acting on the fan is a separate deal.

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      10-02-2019 08:15 AM #6
      Well, always learning something. The radiator temperature fan switch (the sensor in the radiator) was working fine. The fan was fine. The temperature gauge on the dash was working fine. The water pump was working fine.

      The thermostat failed mostly closed!! this overheated the radiator fluid in the engine which the dash temperature gauge showed (that gauge has nothing to do with the radiator temp sensor). Since the radiator fluid was not circulating strongly, the fluid in the radiator was cool, so the fan had no reason to come on. Since the thermostat was partially open, fluid was circulating into the overflow tank since the pump was working.

      I put a new thermostat in and everything is working like it should!! A partial thermostat failure is tough to determine since there is not a clear way to diagnose it in the car.

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      10-02-2019 08:21 AM #7



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      10-02-2019 08:11 PM #8
      Good job!

      I would have never guessed that. Just out of curiosity, does the new thermostat have a small hole in it?

      -OE

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      10-02-2019 08:12 PM #9
      We’re always learning.


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      10-03-2019 08:19 AM #10
      The new thermostat was just out of the box. I have drilled 1/8" holes in the restrictor but didn't think about it this time. It was 8pm when I climbed under the car and when I saw I had to remove the power steering pump bracket to even get to the thermostat.. I figured it was going to be a PIA. I should mention this is my daughter's car, she is a broke school teacher that loves the uniqueness of the car.. things that Dad's do.

    13. 10-05-2019 06:32 PM #11
      Points for being a Dad, or anyone really, who wrenches on folks' stuff.

      Points too for School Teachers, tip o' the hat & a nod of the head in their general direction.

      Points as well for small holes in the thermo's plate.


      Had a problem, Solved it.

      Well Done.

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      10-09-2019 04:19 PM #12
      Quote Originally Posted by Campbell View Post
      Well, always learning something. The radiator temperature fan switch (the sensor in the radiator) was working fine. The fan was fine. The temperature gauge on the dash was working fine. The water pump was working fine.

      The thermostat failed mostly closed!! this overheated the radiator fluid in the engine which the dash temperature gauge showed (that gauge has nothing to do with the radiator temp sensor). Since the radiator fluid was not circulating strongly, the fluid in the radiator was cool, so the fan had no reason to come on. Since the thermostat was partially open, fluid was circulating into the overflow tank since the pump was working.

      I put a new thermostat in and everything is working like it should!! A partial thermostat failure is tough to determine since there is not a clear way to diagnose it in the car.
      THIS is why I have a extra relayed switch to turn the fan on manually. Wiring a indicator light into the hot wire at the fan helps A LOT for understanding what is going on with the cooling system. The stock cooling system is not trustworthy, not even the gauge.

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      10-10-2019 12:38 AM #13
      It's at least as reliable as any other car's cooling system if properly maintained and repaired correctly.

      The later MK1 VWs even had a blinking light if the needle on the gauge going into the red was too subtle.

    16. 10-10-2019 08:11 AM #14
      A stock cooling system is very simple and reliable. The problem is that every part in a 30 year old car is worn out. It's not uncommon to expect items to fail when they are that old. That is why, on my cars, I just swap them out before they fail. The parts are too cheap not to.

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      10-11-2019 12:12 AM #15
      Yes. Old car problems.

      My Ford's heater valve failed recently and it was blowing steam. I had no coolant on the ground because the leak was right over the right exhaust manifold so the coolant was being burned off/evaporated before it hit the ground. Just steam coming out from under the right rear of the hood.

      The coolant gauge was still showing it being cool most times. I knew the general area but had to see it in action to tell where the leak was.

      Even a cooling system on an American car with a V8 and a belt driven fan can have problems when it gets old. The recently replaced generic heater valve (since I owned it) was letting coolant out a vacuum vent hole so I replaced it with an OEM style heater valve.

      Cheap generic parts don't seem to last long on any car, not even my old Ford. I hope the OEM style heater valve last longer than the generic one, but would have confidence in it if it was a Motorcraft or Genuine Ford or even a Delco.
      Last edited by 53PL-50AAA-VW611BAN; 10-11-2019 at 12:28 AM.

    18. 10-11-2019 09:54 AM #16
      You're right, the cheap junk they call parts usually caused more issues than the 30 year old parts.

    19. Member
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      10-11-2019 04:46 PM #17
      Quote Originally Posted by Butcher View Post
      You're right, the cheap junk they call parts usually caused more issues than the 30 year old parts.

      My Ford is a '77. The control head for the HVAC was worn out so I bought an NOS one on eBay. I decided to get all new heater control parts so I also got an OEM vacuum switch, some NOS HVAC vacuum hoses and a parts store special blower switch. I kept the old blower switch because it wasn't dead yet. Fast forward a few years and the new generic blower switch failed and melted the connector. They actually make a pigtail with connector for this very problem. I spliced the pigtail in and put the original 1977 blower switch back in. That was several years ago and I have not had any more problems with the HVAC controls.

    20. Member
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      10-13-2019 08:50 PM #18
      My Ford brakes failed last night so I got it towed home. I was about ready to junk it but by the time I got it home I had forgiven it.

      I parked it on my RV pad and it looks like the right rear hose is leaking or burst, so yeah old cars. Time for a brake job including new hoses.

      Buy new and/or have your butler fix them and take them to the dealer or count on repairing cars.

      They are only new enough not to need repairing or replacing stuff for about 2 years.

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