Why aint my twin rad fans working

Discussion in 'Engine' started by BAZ-500SL, Jul 20, 2016.

  1. BAZ-500SL

    BAZ-500SL Hardcore MB Enthusiast

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    Hello guys, got a issue with the twin radiator fans not working, they are still standing still when the temp is at 100, the auxiliary fan connected to the belt is spinning but the twin fans are not working the car is a mercedes 500sl R129 1990, is there a relay can check I have checked all
    Fuses in the engine bay and in the boot, also why could cause this, the temp is rising and the bottom hose is hot as well at the top so I believe the stat to be fine, I need to check the clutch fan still but my concern is why the twin fans are not working all help is appriciated thanks
     
  2. RichardF

    RichardF Hardcore MB Enthusiast

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    The twin fans are for the A/C
     
  3. OP
    OP
    BAZ-500SL

    BAZ-500SL Hardcore MB Enthusiast

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    I see so they will only work when I got the A/C on not to cool the engine, and the engine cooling is the single one ?
     
  4. RichardF

    RichardF Hardcore MB Enthusiast

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    The engine driven fan provides the main cooling, electric fans are for the A/C.

    If it's an original MB set up they will provide some additional cooling but only when the engines very hot. Make sure your engine driven (viscous) fan is working correctly 1st.

    What's the problem?
     
  5. Mercland

    Mercland Authorised Forum Sponsor Authorised Forum Sponsor

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    All that controls those fans on an early R129 is a relay, fuse and the temp switch on the engine. I would check the temp switch and wiring to it. Its not the one that provides reading to cluster, there is a seperate one.
     
  6. OP
    OP
    BAZ-500SL

    BAZ-500SL Hardcore MB Enthusiast

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    The problem is the engine is getting hot at standstill, I have checked the bottom hose and it's hot so I have know the stat should be ok,no have also checked for any air in the system and it seems to be ok, the big fan is turning but I still need to check if the clutch is working, but these two small fans are not working, but if I put my AC on these should come on ? so that will eliminate that they are ok, I'm just worried that the temp rises and doesn't cool at standstill , it's not loosing any water and everything seem ok I'm that section, but just heats up on standstill, where would I find the relay for these fans and the thermo sensor so I could see if they are ok, thanks again guys do appreciate this
     
  7. hotrodder

    hotrodder Hardcore MB Enthusiast

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    The aux fans are switched according to AC refrigerant pressure and/or coolant temp. They're usually a 2 speed deal that'll run on low speed as necessary for the AC and cut in/speed up if the coolant temp reaches ~110°C and cut out when the coolant drops to ~100°

    The main engine driven fan has a viscous clutch that should 'lock up' somewhere around 100° give or take a few degrees. When they do it's pretty noticable as they make a racket due to the amount of air they shift when fully engaged compared to when they're freewheeling/spinning slowly as the clutch isn't locked up

    If the temp didn't go over 100° there's a good chance nothing's wrong as it's not even close to overheating. Time to start properly fidgeting is if the temp carries on climbing towards/beyond 110 and no fans cut in to bring the temp down

    For peace of mind/reassurance that the fans do work then as said the viscous fan is the place to start along with the coolant temp switch for the aux fans. It's a two pin deal somewhere on the thermostat housing or at the front of the engine. Bridging the pins should energise the fans. There'll also be a single pin sensor near it for the temp gauge and a larger 4 pin deal for the ecu.
     
  8. OP
    OP
    BAZ-500SL

    BAZ-500SL Hardcore MB Enthusiast

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    Hello left the car idling and the temp goes to about 110 degrees the twin fans kick I'm and bring it back down to 105 degrees, I tried to stop the big fan but it's just keeps moving, there is no air in the system, but my concern is why it gets so hot the car is not smoking or losing water and I had her started for about 1-2 hours and she just stays at between 105-110 degrees, any Idea what to check next the car has been stood for some time I should mention
     
  9. brucemillar

    brucemillar MB Club Veteran

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    You need to be certain that your temp readings are what you say/think that they are?

    Where are you taking the readings from?

    The best way to be sure is to use an infrared thermometer (you can get one in screwfix). Point that at the top hose or stat housing when the stat is open. What temp reading that give.

    As hotrodder says you are just about at the trigger point for all you fans. If you are reading from the gauge? that may not be accurate. The gauges are an indicator and cannot be relied on for an accurate reading.

    Ambient temp has an effect on engine temps. The past few days have been very hot in the South East (34c) This impacts on the standing temps as you should expect an increase over the "norm"

    The viscous fan (The one that is cooling your engine/rad): That should not stop when hot. With the engine cold it should turn with some resistance (it should not freewheel) that resistance will increase until the engine is hot 80+ at which point it will lock up.

    Do not be tempted to stop it with your hands (hot or cold). With the engine hot and at idle, use a rolled up news paper and poke it in the blades. If it shreds the paper it is likely to be OK. If it stops then it is failing.
     
  10. RichardF

    RichardF Hardcore MB Enthusiast

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    In a high ambient temp that sounds pretty normal. When you drive the car it should quickly drop down to 80-90c
     
  11. OP
    OP
    BAZ-500SL

    BAZ-500SL Hardcore MB Enthusiast

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    Thanks guys I have tried to stop the big fan with a rolled up cardboard and a metal stick but it just won't let me stop it just keeps going and pushing what I use away from it, the engine does get hot quite quickly , the car when it used to be used did used to drop in temp as it was being driven and as mentioned at standstill it will rise I have felt the bottom hose once switched off and it seems to be hot weather this is due to the heat from the engine bay or the water passing through Im not sure, the temps I'm going from are by the temp gauge on the dash
     

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