Coolant overflow keeps overfilling and coolant level goes down. Why?

Posted by 96gstdsm, Sep 9, 2007
Newbie Forum - Beginner/newbie/general DSM modification questions. First mods, how to run 10's when you haven't run 12's yet, any tech question that doesn't fit in another tech forum.

  1. 96gstdsm

    96gstdsm Proven Member

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    monroe, New_York
    My car has just finished getting many mods, one including a fmic that has been giving me some cooling problems. I have been overheating. The highest I have seen was 224 that was on the hottest day of the year. The temps only get really hot when I am on the highway and only sometimes with the stock needle go up to almost 3/4 to hot. I had a logger hooked up before to monitor the temps but don't have it hooked up at the moment.

    I checked my coolant levels and they were a little low, so I added some water and coolant. My overflow was right at the correct level.
    After driving for some time and then checking it again the next day, I looked and my overflow tank was overfilled and my coolant levels in the radiator and all went down.
    I am not burning any coolant or anything and have no smoke or anything coming out.
    Why does my coolant keep going from my radiator and lines to my overflow tank?
    Could a bad radiator cap cause this? I have a new one I am putting on as soon as it cools down.
    Would just overheating in general cause this?
    Also why would my car only sometimes overheat when on the highway going the same speed and with the temperatures outside being the same. When driving around they will go up and down when traveling at the same speeds. And sometimes during my trip the needle will stay right around the middle line if not below and other times it will be 3/4 to hot.
    The needle acted the same when I was able to monitor the temps as well.
    #1
  2. jiggysnitz

    jiggysnitz Proven Member

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    Woodinville, Washington
    I seem to have a similar problem, every now and then it appears that my coolant level has dropped. My car stays completely perfect temp around town but once im on the freeway the temps start to rise and rise and rise?
    #2
  3. Clay

    Clay Proven Member

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    626, California
    Check for coolant leaks?
    #3
  4. turbosax2

    turbosax2 Moderator

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    Glenshaw, Pennsylvania
    I suspect the radiator cap. Replace it and the thermostat.
    #4
  5. 90gst_sean

    90gst_sean Proven Member

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    Seattle, Washington
    /\ what he said /\
    #5
  6. meliketoball

    meliketoball Proven Member

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    Maybe your FMIC is restricting a lot of the air to your radiator.
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  7. Loewen21

    Loewen21 Proven Member

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    Steinbach, MB_Canada
    Could be a bad rad cap but this is also a classic sign of a blown headgasket, pressure getting into the system and pushing out the coolant into the overflow. Check to see if the coolant is milky or also if there is any coolant in your oil
    #7
  8. JDMHVN

    JDMHVN Proven Member

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    Pewaukee, Wisconsin
    I had the same problem.. Turns out I had a leak in my cooling system by my overflow tank. I replaced the tank and it never happened again. I would start narrowing down where you could have a possible leak and start from there.
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  9. meliketoball

    meliketoball Proven Member

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    Bay Area, CA, California
    COOLANT PRESSURE TEST THAT BITCH! :rocks:
    #9
  10. ricktb

    ricktb Proven Member

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    Edmonton, AB_Canada
    -new rad cap
    -new thermostat
    -purge system of air bubbles, squeeze lower rad hose 10-15 times with engine running and heater on high (rad cap off, bubbles should come to top)
    -top up to brim under cap with 50/50 mix or so
    -fill resevior to low mark on cold engine

    double check upper rad hose gets warm (thermostat open)
    double check fan is on
    double check water pump is spinning

    coolant should stay within the high, and low line or maybe theres other issues then consult the wisemen
    #10
  11. roadrunner2176

    roadrunner2176 Proven Member

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    South Bend, Indiana
    Just another thing to add, make sure your using a proper mix of coolant. And give your exhaust a whiff. Smells like antifreeze and you have a head gasket leak.
    #11
  12. absolute_DSM

    absolute_DSM Proven Member

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    Boise, Idaho
    This is more than likely why the OP is overheating.
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  13. Black 95 TSI

    Black 95 TSI Proven Member

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    Springfield, Virginia
    Sounds like a headgasket to me, My truck did the same thing to me. every few days I would dump the overslow back in the the rad. I finiley checked the thte system with a block tester and OPPS blown hg
    #13
  14. jessdogg

    jessdogg Probationary Member

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    New Castle, Delaware
    check your hose in your overflow tank from the cap. i've seen where the hose doesn't go down like it should, sometimes it folds up if your not careful. that would let coolant drain into the overflow and not get sucked back into the cooling system. hope that helps
    #14
  15. talon187

    talon187 Proven Member

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    torrington, Connecticut
    had the same problem with my 1g was a headgasket the kid that had the car before me put a diffrent head on the car but didnt have it resurfaced so i ended up with a nice head gasket leak
    #15
  16. 96gstdsm

    96gstdsm Proven Member

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    monroe, New_York
    OK well got a new radiator cap and it seems to have fixed the overflow tank filling up to high. My coolant temp gauge(stock) also has not gone over half way really with the ac fan on always since I put the new cap on. I don't have the ecu+ engine management hooked up right now to confirm that the temps have gone down for sure or not though. Will shortly.
    #16
  17. evo9mrtt

    evo9mrtt Proven Member

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    Arvada, Colorado
    I recently had my car compression and boost leak tested by a good friend and everything checked out ok. My compression was 135 across the board and the only leak we could find boost wise was at my throttle body cause my shaft seals are bad. So i ordered new shaft seals and got a new isc. I also replaced my thermostat not even a year ago with a oem unit. I also wired my ac fan to my regular fan so both fans come on when one does. but now my coolant keeps over filling my catch tank and over flowing...a lot. It only over flows out of the catch tank. It seems as if i add coolant everyday. Any clues as to what could be causing this? I don't have any leaks in my system either. Any help or ideas would be greatly appreciated.
    #17
  18. WILOWNU

    WILOWNU Proven Member

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    having the same problem, but when I boost I get a whiff of coolant...not sure if it is coming out of my overflow and hitting my exhaust (becuase my overflow has been moved to be on my firewall) or if my motor is burning it due to a hg blowout. going to put a new rad cap on today and see what it does...if no fix, im gonna do a coolant pressure test and see WTF is up....I will post up results later this evening.:thumb:
    #18

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