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heating troubles now...

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by evilscotsman, Dec 6, 2008.

  1. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 6, 2008]
    flippin heck, whats next?

    the heating is blowing stone cold air, even when the engine is at 90 unless you are driving at fairly high speed, the fans are working, the temperature can be set ok, but even at HI if you slow down or stop, the air turns stone cold. Any ideas?

    Hope its not the water pump, but it doesnt overheat even sitting still, in fact the temp gauge will drop to 50 again when stationary.
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  3. oneninet
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    oneninet New Member

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    [Dec 6, 2008]
    Did you sort out your pressure bottle cap?
    Dodgy thermostat?
    Fan on constant ?
    :uhm:
    #2
  4. Macduff
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    Macduff Member

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    [Dec 6, 2008]
    Temp guage should sit at 90 all the time once it's up there so something is amiss.

    Do you get warmth in the radiator hoses as soon as the engine is started? if so, 'stat is stuck open. Maybe the heater matrix is after the radiator in which case it may never really get warm coolant to work with. Doesn't explain the guage getting up to 90 though.

    The only time I've had a 'stat go was in the bike. It normally runs at 75C but wouldn't get above 50C when the air temp was around 5C
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  5. AndymacA4
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    AndymacA4 Member

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    [Dec 6, 2008]
    I'd usually guess the stat, but given the gauge reads 90 degrees and you still get no hot air at all that's a bit odd.

    SO the car will warm up and stay at 90 when you are going fast, but you still get no hot air? Then if you drive more slowly or stop, the temperature gauge drops down to the 50 mark after a while?

    I'm not sure about the design of the thermostat, but on some cars it is a two stage affair, first opening coolant to the interior for heating, then to the rad for cooling. I'd guess a blocked or trapped heater pipe and a poorly thermostat.

    Have you had a coolant change of late? Could be an air lock in the system somewhere? Anyways, with current weather it is worth getting someone to look at it! :cold:
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  6. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 7, 2008]
    aye an airlock is what im thinking now. I still havent replaced the expansion cap but think its slowly steaming the water away, it didnt complain this time about water level but it started blowing cold air I noticed it was right down below min, filled it up and it didnt cure it. It doesnt overheat ever, but the fan doesnt run all the time either, it will stay around 70 at idle anyway and 90 when driving.

    The air blows hot for a while when you get cruising at 60 but if you stop or slow down it gets cooler and cooler till its stone cold unless you drive again.....frozen stepper flap???
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  7. AndymacA4
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    AndymacA4 Member

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    [Dec 7, 2008]
    If you do get heat at all then the flaps must be working. Try getting hold of a replacement expansion tank cap. Can you get cheap universal ones from motor factors? That should stop the escape of coolant. I guess the hoses for the internal heater are designed to empty before the engine coolant. Most cars use this feature to avoid engine damage if water starts to run low.
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  8. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 7, 2008]
    yeah sounds good andy, will have to get that cap replaced.

    Anyone know where the cabin temp sensor is located? The first problem I noticed is it tried to cook us even at 18 deg setting, then no matter how high it was put it blew cold, so want to make sure the sensor is ok
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  9. jase0851
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    jase0851 Member

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    [Dec 7, 2008]
    there,s 1 sensor in the headlining near the light and 1 on the front of the climate unit where the little vents are. IIRC
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  10. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 7, 2008]
    cheers mate.
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  11. jase0851
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    jase0851 Member

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    [Dec 7, 2008]
    np scots, vag-com would come in handy if you have it.
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  12. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 8, 2008]
    ive got a chinese vag com cable that used to work with 409 and 607 but when 704 came out it broke the flippin firmware in the cable head. I tried to re-flash it, seemed to work but now the laptop says its ok but it doesnt see the car....:(
    #11
  13. Macduff
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    Macduff Member

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    [Dec 8, 2008]
    There's also a sunlight sensor on the middle of the dash near the windscreen. It's the black thing in the middle of the vent. It's possble it could also be causing the issue but it sounds more like one of the temp sensors.
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  14. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 9, 2008]
    it suddenly started working again......

    weird.
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  15. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 10, 2008]
    ok, there seems to be a sucking sound behind the head when i squeeze the top rad hose, water is still escaping somewhere and the cap has been replaced.

    The system doesnt build noticable pressure tho the gauge works normally and reads 90 when warmed up, the fan is running all the time on the rad I noticed today, its just quiet - the heating works as long as the water is at max level, and only when accelerating or cruising at speed - im thinking the rear coolant sensor has developed a leak at the o-ring maybe so low water pressure and the car is trying to over cool to protect itself?

    Short of pressure testing it, has anyone else had this? It sounds like the thermostat from other recent posters experiences, but the sucking sound coming from behind the head is making me wonder about the sensor, as the thermostat is at the front rhs in the pump housing yeah?
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  16. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 11, 2008]
    stat wouldnt really make any noise, it just wouldnt control the temp properly and it would run cold.

    When our stat went the guage would drop to about 60ish while driving (as the stat was letting too much water thru the rad and overcooling the engine), and would only get to 90 if left idling.

    Yours seems to be a different issue however.

    Sucking noise behind the head could be an airlock of some kind or it could be the leak itself...
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  17. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 11, 2008]
    Also, i dont think the car is capable of "overcooling to protect itself" Its more likely that the temperature drops because theres no longer any water around the coolant sensor, so it has nothing to measure.
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  18. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 11, 2008]
    Maybe I post in a confusing way.

    The facts are:

    1. The indicated temperature on the dash gauge is always correct.
    2. The heating, even on high setting, is cool unless accelerating.
    3. The sucking noise happens if you squeeze the rad hoses.
    4. The rad fan runs continuously.
    5. The water disappears from the header tank over the course of a week.

    Cheers all.
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  19. ozique
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    ozique Member

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    [Dec 11, 2008]
    I have same problems as yours. When in traffic, it becomes cold, so when car is in motion, it get warms.
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  20. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 11, 2008]
    annoyin aint it?

    Im gonna get the system pressure tested.
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  21. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 12, 2008]
    What i'm saying is the facts dont make any sense?

    IE the engine when left idling while stationary will get hotter, not cooler. The only two things that i can think of that could cause that, is an airlock forming around the temp sensor, so the sensor is reading nothing, or the stat being stuck open AND the fan managing to cool the engine down enough to lower the temp to 50c.

    When our stat was gone the only time it would reach 90c was when idling in traffic or similar, if we were moving at all it would quickly drop and high speed motorway driving would see it drop all the way to 65ish.

    You say the fan runs all the time, isnt it viscous coupled? ie it will run all the time? It is on the B5 anyway. If the VC is working you should be able to stop the fan with your hand with the engine at normal temp (although dont stick your hand in it incase its broken, use something else)

    So either the guage is lying, or the stat is stuck open AND the rad fan is somehow managing to keep the engine cold (which is unlikely, but possible i guess?)

    You need to find the source of your water leak, i think its far more likely you've got a leak and its introducing airlocks into the system, when accellerating the raised RPM might be managing to shift some of them and actually circulate water round the heater matrix properly.

    Heres what i'd do, ensure the water is full, drive the car around for 10mins to get it warm then park, leaving the engine running, open the bonnet and feel the rad hoses (both of them), they should be hot, and firmish. If they're still soggy the system isnt pressurising, and its probably spraying water out the leak, have a look round the engine, listen for hissing and see if you can see crystalised antifreeze anywhere. Also compare the dash temp with the temp of the hoses, 50c is just about holdable, 90c is "owch thats fricking roasting"

    See what you come up with.
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  22. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 14, 2008]
    yeah the hoses are soggy and not pressurising, I noticed that last week.

    will have a serious look for a leak tomorrow in the daylight. The fan is electric and mounted on the rad next to the automatic blind that controls airflow thru the rad on warm up.

    :)
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  23. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 14, 2008]
    Ye it seems like some of the B6 models have single or twin electric fans and some use viscous coupling. B5's are all viscous hence my confusion

    Does the car have aircon? It may run the rad fan if the aircon is on, which might be confusing matters?
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  24. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 14, 2008]
    yup it has aircon but when set at 20deg as it is cold just now, it doesnt run the compressor, just supplies heat. Theres no visible signs of leakage like puddles etc, just the gradual loss of coolant from the header tank over a week and erratic cabin heating.
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  25. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 14, 2008]
    My bro's S4 runs the aircon even in these temps if its on "auto". No idea why, but if you select Auto or Windscreen demist on the climate unit it kicks the aircon on...

    I think it does it to dry the air, because if you click the aircon off manually the windows tend to steam up for a few minutes
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  26. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 14, 2008]
    hmm mine might do as well then, your right i did get steamy windows when i put it on econ one day....
    #25
  27. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 15, 2008]
    I think that econ button turns the AC off.

    On the S4 there is a button that looks like a snowflake and a corresponding symbol on the display, When you press auto or demist the snowflake appears and the AC fires up, regardless of the desired temperature. If you then press the snowflake button the AC cuts out and the snowflake disappears.

    If you don't have a snowflake button/symbol, try switching on econ and seeing if the rad fan stops.
    #26
  28. bhdseller
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    bhdseller New Member

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    [Dec 15, 2008]
    I have just logged into this forum to see if anyone was having the same problem and found this post!! It's exactly the same for me. I have an a4 Cab and when I'm driving slower, it's cold, and as soon as I get up to around 3000rpm, it starts blowing hot air. The only thing worth noting for me is that I had a Coolant Warning light come up the last few days, which is around the time this heating problem happened. I have topped up the coolant as it was way below Min level (worryingly), but the heating is still not working properly. I'd be interested to see if anyone has any other ideas... I might have to take it to a garage tomorrow though as I don't fancy my daily commute in 1deg temperatures... thank god for heated seats! :beee:
    #27
  29. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 15, 2008]
    I got the coolant warning a few times too and the water was below the min, now it doesnt warn me any more, just gradually disappears. I think I am going to have to get it pressure tested at a garage, as there is no sign of water leaking out as far as I can see anywhere, unless its a small trickle and getting vapourised.

    I did notice a wee puff of steam from the front grille, but when I opened the bonnet it was gone, thinking maybe pinholes in the rad somewhere ?
    #28
  30. AndymacA4
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    AndymacA4 Member

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    [Dec 15, 2008]
    Try a tube of rad seal, it is a bit thuggish, but does the job on very small leaks like rust pin holes in rads?
    #29
  31. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 16, 2008]
    bhdseller: The problem is down to the water leaking out and airlocks forming in the heater matrix. If your going to be driving the car, ensure you top up the water, and check it EVERY time you drive the car, until you find and cure the leak. You will find if you top the water up fully and bleed the heater matrix your heat will return, until the level drops again. If you top it up continually and dont let the level drop, the matrix should stay airlock-free.

    as i suggested to evil, once you've topped it up (and bled it) go round very carefully with the engine running and hot and see if you can find the leak. A visual inspection might also uncover the leak as antifreeze will leave white/brown crystalised deposits around where its leaking from.
    #30
  32. golf
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    golf ***** rent boy VCDS Map User

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    [Dec 17, 2008]
    I had this problem, it slowly got worse where the air was cold all the time rather than only at higher revs. Thought it was an airlock or the thermostat, but turned out to be the bloody water pump. Could be the case with yours too.
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  33. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 19, 2008]
    yeah that crossed my mind mate :(
    #32
  34. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Dec 19, 2008]
    Usually when the waterpump dies it will overheat pretty quickly. The heater stops blowing hot because theres no circulation, but the engine would still overheat and you'd know about it.

    It also doesnt explain the loss of water, unless you can see the water pissing out the hole in the pump casing...
    #33
  35. evilscotsman
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    evilscotsman Space Cowboy

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    [Dec 21, 2008]
    ok, im beginning to wonder i the head gasket is involved in this.....the exhaust is very steamy even when fully warmed up and after a brisk drive for an hour, outside temp was 5deg, and the white smoke from the exhaust was very visible when sitting in the petrol station. It smells pungent but not oily etc, and feels extremely damp on your hands.

    Theres no mayo inside the oil cap but the expansion tank smells "enginey" inside (lol) - maybe theres a tiny HG leak between the water jacket and a cylinder?
    #34
  36. evilscotsman
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    evilscotsman Space Cowboy

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    [Jan 25, 2009]
    i tried a test - driving at a fair lick (70) the heat appears, so I slow down coming into the village, and the air turns cold. I pull over, and while its sitting still and blowing cold, I revved the motor to 3k and held it, the heat instantly returned, then disappeared just as quick when I let the throttle go again.

    I now beleive its the water pump, anyone got an idea of cost to replace at a garage?
    #35
  37. Emmo
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    Emmo Member

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    [Jan 26, 2009]
    Mines had a similar issue before the new year. Coolant was disappearing and no heat from the heaters sometimes.
    Turned out there was a leak from the coolant flange at the back of the engine. After this was replaced there was no coolant loss. The heaters still ran cold, soI took the top off the coolant reservoir and ran the engine for 5-10 mins which got rid of the airlock and the heating was back to the normal roasting hot.
    #36
  38. evilscotsman
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    evilscotsman Space Cowboy

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    [Jan 26, 2009]
    cheers mate that fits perfectly with what ive been getting, I noticed tonight that if I spent a while letting the bubbles out with the cap off the heat works even at low speed, so its just leaking and drawing air. DOH!

    I guess that a coolant flange may be in order but its a real bitch to see down there, god knows what its like to change it.....garage job I reckon unless you guys have done it at home?
    #37
  39. Emmo
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    Emmo Member

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    [Jan 26, 2009]
    The flange is actually a £13part, but is a bit awkward to get to,I left it to my local specialist, got it sorted in no time.
    #38

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