Cannot purge air in coolant system BHW B5.5 2005 Passat TDI

Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by Adam Chasen, Oct 4, 2017.

  1. Adam Chasen

    Adam Chasen New Member

    Joined:
    Oct 4, 2017
    Messages:
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    Car:
    Passat TDI GLS 2005
    Location:
    Raleigh, NC
    I had to change a stuck open thermostat in my 2005 BHW B5.5 Passat which opened my coolant system. All coolant I drained from the radiator looked like it was in great condition. Everything went well and now my engine temperature doesn't drop on the highway.

    Since then, I have had the occasional gurgle in my dashboard, but seems more likely when under load. AC system is not on, so it is not refrigerant. Heat appears to work just fine.

    I have performed multiple incarnations of the purge process with the weeping hole on the hose. Engine on, engine off, coolant cap open, coolant cap closed, lifted reservoir, etc. I thought it would purge itself over time, but it doesn't seem to.

    I did not backflush the heater core or oil cooler. Is it possible air bubbles are getting trapped in the heater core? I can't imagine that my heat would work well at all if the core were blocked to the point of holding back air.

    I would like to prevent the gurgling, but isn't worth a ton more time investment. Is there any issue with air in the system? I recall reading corrosion or wear issues. Any pointers on the next steps?
     
  2. Peca

    Peca Member

    Joined:
    Jun 12, 2013
    Messages:
    113
    Car:
    Passat b6, 2007, 103 KW
    Location:
    Pale, Sarajevo BIH
    Engine temperature should be constant it should not drop at any time when engine goes to operating temperature. VW engines should purge themself, you have to check if radiator hoses are hard after driving at the end of the day. If they are hard it means the additional air comes into cooling system. If they are normal you should replace heater core under the dashboard.
     
  3. Adam Chasen

    Adam Chasen New Member

    Joined:
    Oct 4, 2017
    Messages:
    4
    Car:
    Passat TDI GLS 2005
    Location:
    Raleigh, NC
    From where I have squeezed so far, they are not hard (hot, yes). Are there any hoses I should specifically check?

    I believe the system is under pressure quickly after starting. Wouldn't there be (big) leaks?
     
  4. Peca

    Peca Member

    Joined:
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    Messages:
    113
    Car:
    Passat b6, 2007, 103 KW
    Location:
    Pale, Sarajevo BIH
    The hoses should not be to hard, especially after starting. When the engine is hot they should be a little harder then cold but not to hard. I think you have a head gasket problem.
     
  5. Adam Chasen

    Adam Chasen New Member

    Joined:
    Oct 4, 2017
    Messages:
    4
    Car:
    Passat TDI GLS 2005
    Location:
    Raleigh, NC
    A head gasket problem would be very sad news. Would (replacing) a stuck open thermostat exacerbate a head gasket problem? I do not recall having this issue before I replaced the thermostat (and introduced air into the coolant system). Any tests I can do? Any common weak points I can visually inspect? Would I see coolant leaks if the hoses or fittings had any issues?

    The coolant I pulled out of the car and in the reservoir and what has come out of the weep hole when bleeding after the thermostat switch appears to be clean. Would some introduced exhaust due to a small gasket problem make a visible/noticeable impact to color/smell?

    I am going to change the oil this weekend and will check for any contamination, but once again, would a small problem show?
     
  6. Peca

    Peca Member

    Joined:
    Jun 12, 2013
    Messages:
    113
    Car:
    Passat b6, 2007, 103 KW
    Location:
    Pale, Sarajevo BIH
    If you had not a problem before thermostat job I doubt you have a head gasket problem. You just have an aditional air in system but I don't know how that happened, I changed a lot of thermostats and never had that problem. You have to go to your garage or dealer for precisely diagnose.
     
    Last edited by a moderator: Oct 13, 2017
  7. Adam Chasen

    Adam Chasen New Member

    Joined:
    Oct 4, 2017
    Messages:
    4
    Car:
    Passat TDI GLS 2005
    Location:
    Raleigh, NC
    Thanks, will probably inspect a bit more thoroughly. Am I correct assuming that any crack or other "opening" which could introduce additional air into the system would likely leak coolant as well?

    Is anyone familiar with the the mechanism used to bleed air from the liquid loop in the sealed system? (not the weep hole, but how air is "purged" when in operation and sealed) I see the small hose at the top of the coolant outlet from the engine and believe that is the mechanism, but not sure. It also slopes down which I thought was a bit odd, but maybe that is to provide a little back pressure on the port to prevent a venturi effect of pulling air from the reservoir into the liquid.

    Any other troubleshooting tips? What would be the next step for a garage?
     

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