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  1. #1
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    Aux. waterpump hiccup. Strange sucking sound. Why?

    Today I noticed some weird stuff happening with my car:

    -the interor lights briefly dim slightly every 2 seconds.
    -there is a regular whining sound changing briefly pitch every 2 seconds. It's like a hiccup.
    -about two seconds after turning off the engine there is a brief but quite loud sucking noise coming from somewhere under the hood that lasts for less than a second.

    The whining sound is there both with the engine running (engine hot) and with the engine turned off and the key at position 2.

    The sound comes from where the aux. waterpump is located and I'm pretty sure it's the pump itself making that noise because -with the engine off and key at position 2- I can feel the radiator vibrate and I can also feel the thick upper water hose pulsate with the same rhythm as the whining noise when pinching the hose with my hand.

    Is this the auxiliary waterpump on its way out or is there something else going on?

    And what's that sucking noise? A vacuum leak maybe?

    I just had my coolant changed and waterpump and pullies replaced. AFAIK, my mechanic properly bled the engine afterwards. The engine idles fine, pulls as it always has and mileage is a decent 8.5L/100km >> 28mpg.

    The car is a 2002 525iT with automatic transmission and 68,000 miles on the odo.

    Any tips or info is well appreciated.

    Gadjo

  2. #2
    Craig in Canada
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    Re: Aux. waterpump hiccup. Strange sucking sound. Why?

    You didn't mention checking the coolant level.... :) Clearly not everything you've mention necessarily relates but it's still wise to check. Remember to check cold.




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    Coolant level

    The coolant level indicator -with a lukewarm engine/coolant- is some 2.5cm (1 inch) below the top of the filler hole (=max. position).

    I will check tomorrow morning to see how far it drops when the engine has cooled down completely and top off if necessary to the top of the filler hole.

    Gadjo

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    Coolant level corrected, still hiccup sounds,

    I had to add roughly a coffee cup of coolant (0.25L) to fill it up at the max with a cold engine. The hiccup is still there.

    What I did find out is that the hiccup is caused by the IHKA heat valves that regulate the cabin temperature. When I set the cabin temperature at its lowest (60F), the aux pump is shut down or runs at a regular speed without much noise or hiccup. When I set the temperature at the max, the pump hums a bit louder but also without hiccup. When it is set around the normal temperature (70F), it will hiccup. Maybe, the hiccup is noticeable when the pump is worn out and not if the pump runs smoothly by itself?

    I did some test at idle with brake cleaner to locate a potential vacuum leak that might cause the brief sucking sound after engine shutdown. No results so far: idle stays steady wherever I spray around the intake gaskets and hoses. Maybe a faulty CCV? How can I quickly diagnose a faulty CCV?

    Gadjo

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    Craig in Canada
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    Re: Coolant level corrected, still hiccup sounds,

    I've heard the valves (not the pump) thump from time to time when they are being cycled at a setting which is not 100% on or 100% off. Is this possibly what you're hearing?


  6. #6
    Miniron
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    Heater Valve and Aux Water Pump Operation

    Mine does the same. M52TU engine is similar to the M54 engine regarding the cooling system and heater/climate control.
    The heater valves are only ever fully open or fully closed at max or min temp settings. At all other intermediate temp settings the valves pulse open and closed at intervals of between o.36 secs and 3.6 secs.
    You can feel this by touching the heater valve assembly and you will feel a slight thump for each click. You can also feel the radiator hoses pulsing at the same time. If you have INPA software you can see the valves opening and closing on one of the digital indicator dislays.
    I haven't been able to work out if the auxilliary water pump runs all the time or only at low engine speeds or large thermostat openings to maintain adequate water flow through the heater cores. Does anybody know? I can't drive and look at INPA at the same time.

    Hope this helps.
    RonR
    99 528iT M52TU

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    Ed CT
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    Re: Aux. waterpump hiccup. Strange sucking sound. Why?

    Sucking sound: Check the brake booster vac line that goes from the intake manifold across into the area under the driver side cabin air filter. The tube goes thru the metal framework and connect to the booster underneath the brake/clutch fluid reservoirs. The hose may get brittle and crack over time.

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    Re: Aux. waterpump hiccup. Strange sucking sound. Why?

    Thanks for that tip. I didn't check that part yet. It will allow me at the same time to check for clogged drains in that area to make sure that I won't experience an immersed brake booster and a potential hydrolock nightmare.

    I did spray with brake cleaner spray around the intake manifold, DISA valve and intake hoses/elbow/AFM but no result.

    I also read about a leaky CCV possibly causing sucking sounds. Do you know how I can quickly diagnose this part without taking it out?

    Gadjo

  9. #9
    Ed CT
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    Re: Aux. waterpump hiccup. Strange sucking sound. Why?

    You have the more complex CVV. You can test the crankcase vacuum by simply removing the oil filler cap while the engine is idling, and seeing if there's a slight vacuum - place a piece of notebook paper over the filler opening, and there should be a slight vacuum that holds the paper against the hole, with maybe a small depression of the paper over the hole.

    Gadjo, also don't rule out that the sucking sound is actually a hissing-depressurizing sound, esp. if there's positive pressure in the crankcase, or, (hopefully not) a leak in a pressurized fuel line.

    Have you tried listening at the engine bay immediately after the engine is shut off to locate the sound's source?

  10. #10
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    CVV check okay

    Hi Ed,

    I checked the CVV per your description and the paper on the oil filler hole behaves exactly like that. I also checked the vacuum line to the brake booster; no abnormalities found either.

    The brief hissing sound is difficult to locate. It seems to come from somewhere below the DISA valve but I can't tell for sure. I had someone else to start and shut down the engine a couple of times while I was listening closely to where the sound seems to be coming from. Maybe I should do a smoke test.

    I'll give it a rest for now; the car drives and idles fine. The only thing left to do is to re-bleed the engine to make sure there's no trapped air left. My aux pump has started to whine since the recent coolant flush/water pump replacement.

    Thanks for your advice.

    Gadjo

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    ? New reservoir may be defective???


  12. #12
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    Interesting write-ups!

    Thanks for sharing.

    However, I still have cabin heat and still the original radiator + expension tank. So I don't think I have a flap restricting/blocking coolant flow.

    But I will have those parts replaced as well in the foreseeable future anyway since end-of-life of these parts is coming soon anyway at 9years/68kmiles. Your links prove this once more.

    I already replaced a faulty thermostat, preventively replaced main waterpump + pulleys + belt. So radiator + expension tank, aux waterpump and all hoses will be next. I'd rather be on the safe side than run into an overheating engine. I might even opt for a Zionsville; money is not really an issue when it comes to improving the reliability of the cooling system on my car since I plan to drive my E39 till the very last end.

    To be continued.

    Gadjo

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