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Sucking air into coolant system

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by abiggerjimjr, Apr 30, 2013.

  1. abiggerjimjr

    abiggerjimjr New Member

    Feb 6, 2013
    Likes Received:
    [Apr 30, 2013]
    Ok guys, I've searched and searched and searched, and although I've gotten help from my searches, it's time to pose my own question.<br />
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    I have a 2002 A4 Quattro 1.8t engine code AMB (I think that's all the info you might need). I recently did a head gasket, metal impeller water pump, timing belt, thermostat, etc. job and ever since I've put everything back together, I've been fighting the infamous air bubble problem. I learned a lot about bleeding through various searches, and yesterday, after 20-30 minutes if bleeding and a big top off or two, I thought I finally had the problem solved. I had been experiencing a problem where I would run at normal temp until I got on the highway and ran for 10-15 minutes, then the temp gauge would quickly run up into the red in between 15 and 30 seconds. I would pull over and shut it down, of course (don't want to ruin my brand new head gasket), and steam would be coming out of the pressure relief in the reservoir tank. I decided I must have been having air pockets catch in the thermostat causing it to not open and therefore overheat the motor. After being on the highway for 20 minutes yesterday at normal temp, I thought I had all the air out and the problem solved, but there again went the temp gauge. I immediately put the heater on full blast, but there was no heat coming out if the vents. Sure enough, I found air in the system. My best guess is that there is a clamp that is not quite tight enough and that it's letting air leach into the system under higher revs/ coolant flow. I've already replaced all the problem parts, t-stat, both coolant temp sensors, and the rear flange. I need help from all you experts out there on where to start to find a connection that would have negative pressure during engine operation that would cause it to suck air if the clamp wasn't sealing tight enough.<br />
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    I should also add that I've found if I drive at around 60 mph instead of 70 mph, I don't seem to have the same air leeching problem, or at least it isn't anywhere near as bad because I haven't overheated yet while driving at that speed.<br />
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    Help, please!
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