260e 124 series, overheating

Discussion in 'Engine' started by emimec, Apr 18, 2015.

  1. emimec

    emimec Active Member

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    I ask if anyone can tell me please where the small electric pump, near the water expansion tank, is supplied power from, and when the motor should run. My one doesn't seem to be running unless of course it's due to temperature control somewhere
     
  2. hotrodder

    hotrodder Active Member

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    The aux coolant pump has nothing to do with coolant temp/engine overheating. It's a 'booster' pump for the heater. I'm not sure exactly how it's used i.e. whether it's simply on or off and switched by the heater or a variable speed/pulsed deal according to heater settings etc. http://www.w124performance.com/service/w124CD1/Program/Climate/83-630.pdf doesn't exactly go into much detail but suggests to me (possibly wrongly) that it'll only run flat out when the heater is 'working hard' hence setting to defrost and feeling the pump?

    If the aux pump isn't working i'd expect the heater output to be poor when the engine is idling and/or heat demand is high due to temp setting. Especially if the heater fan is set highish for demisting/defrosting. It'll be listed on the fusebox cheat sheet (both in your owners handbook and in the lid of the fusebox) somewhere, it's supplied by fuse #7 on mine along with duo valves and various other aux fans, HVAC bits and pieces and the reversing lamp

    If the engine is running hot then you need to look elsewhere... tired/knackered radiator and/or main waterpump, dead viscous fan, dodgy thermostat etc. A better description of how the car overheats may help us narrow things down
     
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  3. OP
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    emimec

    emimec Active Member

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    Thanks for the info
    Problem is what seems common with these cars. Normal temperature when driving, but then increases alarmingly, nearly into the red, when In traffic. But reduces as soon brunt get going again.
    I noticed water loss, and bubbling noises near the brake master cylinder, then on another occasion, Brown water marks over the expansion tank. Also, water coming out the overflow by front wheel.
    When I checked water level today, cold engine, noticed a steady drip from the booster pump plastic housing with the rad cap off. Checked later when hot, and under pressure, nothing dripping. This is why I suspected this pump
    Bob
     
  4. OP
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    emimec

    emimec Active Member

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    Predictive text error, brunt. Should read, as you.

    Car had head gasket done about 2 years ago,
    Up until recently, car ran normally at just under 80c, and not much more if in traffic.
     
  5. carat 3.6

    carat 3.6 MB Enthusiast

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    As Hotrodder said, a worn out waterpump, radiator, or viscous fan can cause your overheating issue. Or the head gasket could be on it's way out again.

    I'd look at how old those components are, and do a pressure test on the cooling system.
     
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  6. grober

    grober MB Master

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    Viscous fan coupling is the most likely cause. DO THE CARROT TEST to check its engaging when hot. However dripping from the booster pump requires investigation. Brown sludge in the expansion tank is classic CHG symptom altho this could be historic I suppose - check under the oil filler cap for white mayo or streaks of white tracer in the oil on the dipstick. An examination of all the plugs can be informative- a plug in a defective cylinder will look oily and black that's because its wet! Usually its the cylinders at the rear of the engine that go faulty as they are supposed to run slightly hotter.
    BIG question was the head professionally skimmed when the CHG was done last- if not then its likely the CHG has gone again. If you suspect the CHG get a garage to do a coolant head space "sniff test" with an exhaust gas analyser for combustion gas presence- easy and cheap to do and gives a good indication.

    ps it could be as simple as a dodgy cooling system pressure cap but best to check all possibilities.
     
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    emimec

    emimec Active Member

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    It's not the head gasket. It was done professionally, and none of the usual warning signs. Last time radiator was filled with thick cream.
     
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  8. grober

    grober MB Master

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    Viscous coupling on the fan would be next on my list then.
     
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  9. OP
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    emimec

    emimec Active Member

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    Viscous coupling makes sense, problem i have has become apparent more since the warm weather, and heater not being on, subsequently, the air con fan hasn't been on to assist with cooling.

    In the first posted answer, comment was to check if the electric pump works by pressing DEF. I don't appear to have anything with that on in my car. Unless it relates to the air con buttons, top one seems to clear windscreen, middle button looks like a snow flake, bottom one is E, I think, and never really knew what that was for. Car is a 1991, 124 petrol, 260e. Air con has label saying it's upgraded to new refrigerant.
    Bob
     
  10. WDB124066

    WDB124066 MB Enthusiast

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    Another thing to check; There is a red over pressure switch installed in the AC gas circuit that can malfunction and prevent the electric fans from coming on. This is especially noticeable stuck in traffic with AC on. Question is, does the car behave normally with AC off - if so it may be this switch that lets the electric fans know to turn on that is malfunctioning..... A004 820 68 10 from memory.
     
    Last edited: Apr 19, 2015
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  11. optimusprime

    optimusprime MB Enthusiast

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    aug pump

    Must say that you can break open the plug 12 volt connection ,if you have one on the pump , thats if it is like mine .As i found they fitted one or two types of these auxiliary water circulation pumps. Some just plug right on to the end of the pump .I know a few have removed them and fitted a pipe and hose clips on to do away with the pump .This problem i have had last week ,my auxiliary pump was leaking coolant .So to cut it short i purchased a new one .To check it take a 12 volt supply to it from your battery ,REMEMBER BROWN WIRE IS EARTH..pull back the insulation and it will let you see the colours of the wires. I read in the Mercedes workshop manual that its important to keep this auxiliary pump in situ because the water pump on 260e is not sufficient to keep water temp correct .And i know some have bypassed it with a pipe connection and hose clips. And if you do want to replace any part inside the pump you wont get any spares for it ..other than you can make up brushes if you realy need to.
     
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  12. OP
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    emimec

    emimec Active Member

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    Did a couple of tests this morning. Engine cold, removed coolant cap, water drips from auxiliary pump, doesn't do this until cap is removed though. Ran engine, No drip from pump, which seems odd.
    Tried all sorts of heater control combinations, but my pump, and spare one, never run, so would really like to know what and when turns this on.
    Got a carrot, so will go for a drive latter and do test on fan.
     
  13. grober

    grober MB Master

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    One possible explanation is the leak is elsewhere- say the rubber return pipe to the engine and running down to the pump along the pipe. It would leak because when the engine cools it creates a slight vacuum in the cooling system which might hold the coolant in, removing the cap on a cold engine releases this allow coolant to escape. The leak might be present when the engine is running but the coolant is being blown away rather than running down the pipe so you don't see it. TAKE A CLOSE LOOK AT ALL THOSE FLEXIBLE PIPES
     
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  14. OP
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    emimec

    emimec Active Member

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    It's definitely from the plastic end of the pump, leaks in 2 places, both where the two halves join, steady drips. I have one, slightly different, but the same, if that makes sense, probable it's from my 1992 donor car and an updated version, electric plug is the same.
     
  15. OP
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    emimec

    emimec Active Member

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    Says your banned, so I won't follow your link you posted
     
  16. OP
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    emimec

    emimec Active Member

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    Did the carrot test this morning after a short run, but traffic, so it got up to 80, then left it idling for a while, to just over 80. No luck, carrot stopped fan blades and minimal damage to the carrot. I think it just was not hot enough for the viscous coupling to engage. The more I think about this, I think the problem is basically water loss from the auxiliary pump, this then let's the engine overheat in traffic is insufficient coolant, don't recall any warning lights though.
    I guess I'll wait for more water loss before trying the carrot again to confirm the coupling before changing pump.
    Bob
     
  17. WDB124066

    WDB124066 MB Enthusiast

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    VC cut in temp is from 96 to 104 Deg C.
     
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  18. optimusprime

    optimusprime MB Enthusiast

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    Emimec as you auxiliary pump have square slots? and if so is this the place it leaks from .Then the seals have perished over time. Mine had been on the car 26 years never changed till last week. Have you checked fuses,? I think it runs none stop .I will check it for you .And find how it works ,i do know that the brown wire out of the pair is EARTH ,black is live .
     
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  19. optimusprime

    optimusprime MB Enthusiast

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    info

    Checked this out auxiliary pump should run as long as the ingnition key is in start possition. So your axiliary pump runs all the time. Did you check it with 12 volt bulb.? with ingnition on .
     
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  20. OP
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    emimec

    emimec Active Member

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    I also had a feeling it ran all the time. I plugged a spare pump in, didn't run. Think it's fuse 7, which looks ok
     

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