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  1. #1
    Established Member Two Rings
    Join Date
    Jan 25 2015
    AZ Member #
    Phenix City, Al (was Mich.)

    Coolant temps high, radiator only warm, erratic overheating...4.2 FSI

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    Hello Audi Gang! Well my Q7 has been running well for quite some time with no issues at all. Yesterday...I got stuck in a traffic jam that lasted for nearly 2 hours, but the traffic wasn't totally stopped, so we had to creep along at a speed just below was awful. Anyway when we finally got moving I drove maybe 2 miles and heard the "low coolant" alarm..I looked and also saw the temp was very high. I immediately pulled over and shut down. As soon as I shut the engine off, the cooling fans started running and the auxiliary water pump started running....just like normal. I waited maybe 10 minutes and started her up, temp right at normal, so off I went...only had about a mile to go to get home, and the temps stayed right at normal. I attributed this incident to being stuck in that traffic jam. Well today I started off on a highway drive and made it about 12 miles and then the temps started climbing again. I pulled over and did the same as down a bit....start-up and turned around and headed for home. The temps stayed normal for about 5 miles and then started climbing again, pull over, cool down, restart.....made it back home okay. Popped the hood and looked around, a bit of coolant was bubbling around the expansion tank fill cap, the expansion tank was hot, but the radiator was only luke warm. I slightly loosened the expansion tank cap, and it sounded like an old percolator coffee pot..gurgling sound, expel air....repeated maybe a dozen times. Finally when the system was done making noise I took the cap off and looked down into the tank, no coolant in it. Is it possible that there is or was air in the cooling system, or the system was low on coolant, likely both? I'm going to get some coolant and fill the system back up with the engine running and the heater on full....and drive it again and see what happens. There must be a leak in the system somewhere that I need to track down. It possible that there has been a small coolant leak for some time, that went unnoticed, the coolant level got low and an air pocket developed. I'm also wondering if the thermostat could have failed in the "closed" position?

    Inputs welcomed....thank you.

  2. #2
    Veteran Member Four Rings SQive's Avatar
    Join Date
    Apr 26 2014
    AZ Member #
    My Garage
    2012 R8 GT; 2016 SQ5; 2017 Q7

    The bubbling was just steam, because of over-heating. I doubt it's the thermostat or it would be getting hotter from the start. Once it's opened and flowing, it couldn't just stick closed. It could be a failing/leaking water pump is the likely culprit. Make sure there is no coolant in your oil, which would indicate head gaskets. Personally, I would have at least topped it up and rechecked it with a good, old-fashioned pressure test before posting. Perhaps it was just low because of an acceptably small leak.
    2012 R8 GT, Suzuka with carbon fiber (#298 of 333)
    2017 Q7 P+, Ink Blue, Pistachio Beige, Warm, Vision, Bose, Towing (wife's ride)
    2016 SQ5, Sepang, Black Optic, Technology, BBS CH-R Gold 20x10.5 with 295's
    -2014 SQ5, Monsoon, Sans pano, totaled by a Xanexed-out broad in a Denali XL


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