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    Thread: Why is my coolant boiling over but car isn't overheating?

    1. 05-16-2005 11:55 PM #1
      My 1994 passat glx will boil over the coolant from the vent on the resivoir bottle, but the gauge inside reads fine. I haven't checked to see if the gauge or its sender is bad, but it climbs normally while the car runs. Any ideas?
      Also the passat is hard to start if it sits for a while (couple days). It takes about 20-30 secs of continuous attempts (holding the key) to get it to start. Once it starts, restarting is a breeze with NO hesitation. Any idea on what this could be?
      Thanks

    2. Senior Member TBT-Syncro's Avatar
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      05-17-2005 12:30 AM #2
      thermostat is seized closed.
      leak in the hot side causing a pressure drop, which causes low temp boil over.

    3. 05-17-2005 12:31 AM #3
      Thanks alot for the quick response...I'll check that out ASAP

    4. Member
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      05-17-2005 01:18 AM #4
      Quote, originally posted by TBT-PassatG60 »
      thermostat is seized closed.
      leak in the hot side causing a pressure drop, which causes low temp boil over.

      I don't agree. When my thermostat got stuck closed, my coolant temperature gauge went all the way into the red and my radiator fans went on their high setting, but my coolant never boiled over. It sounds to me like there might be a problem with the cap of the coolant tank not holding the pressure properly, or a leak in the coolant tank itself.
      Kenji

    5. 05-17-2005 02:48 AM #5
      Quote, originally posted by Kenji »

      I don't agree. When my thermostat got stuck closed, my coolant temperature gauge went all the way into the red and my radiator fans went on their high setting, but my coolant never boiled over. It sounds to me like there might be a problem with the cap of the coolant tank not holding the pressure properly, or a leak in the coolant tank itself.

      what i think it is but we'll wait for the poster to respond! I would check the o-ring on the coolant cap. also if that thermostate is stuck closed, squeeze all the coolant hoses you can, some should be rock hard, others easy to compress (hard=after waterpump but before thermostat, soft=after thermostat)

      Onto your starting problem, a wild guess could be that perhaps the fuel pump is not priming for a cold start, but once running fuel is throughout all the lines hence the easy starting. Like i said a wild guess never looked into a problem like this just speculating.


    6. 05-17-2005 01:38 PM #6
      Quote, originally posted by Dubluva »
      My 1994 passat glx will boil over the coolant from the vent on the resivoir bottle, but the gauge inside reads fine. I haven't checked to see if the gauge or its sender is bad, but it climbs normally while the car runs. Any ideas?
      Also the passat is hard to start if it sits for a while (couple days). It takes about 20-30 secs of continuous attempts (holding the key) to get it to start. Once it starts, restarting is a breeze with NO hesitation. Any idea on what this could be?
      Thanks

      Looks more like a blown head gasket, maybe due to overheating. Does the coolant has a brown colour? Or are there any bubbles coming up to the coolant reservoir with running engine and the reservoir cap removed?


    7. 05-17-2005 07:19 PM #7
      The coolant is new..there was none in it when i bought the car (2 weeks ago)..one of the coolant hoses was removed, so the coolant boiling over is the right color. Haven't seen bubbles in coolant when car running with cap off, but i'll check that and the hardness of the hoses and post findings.




      Modified by Dubluva at 7:21 PM 5-17-2005


    8. Member Vdubsolo's Avatar
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      05-17-2005 07:32 PM #8
      I agree with the fact that it might be the seal, O-ring....For the cap.....

    9. 05-17-2005 08:05 PM #9
      might be the cap o-ring or could be a blown headgasket, the exhaust gasses are pushing into the cooling system, you can buy a dye you put in the coolant to check for exhaust, and it will change color if there is exhaust present.

    10. Member Sn0wMaN's Avatar
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      05-17-2005 08:33 PM #10
      Doubt its a headgasket, your system is loosing pressure somewhere causing low temp boil which was stated before. Do the hose squeeze thing and see if you have pressure.
      91 GTI VR6 - 13.8 @ 98
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    11. 05-20-2005 10:29 PM #11
      Okay..I added coolant today, started it up and let it run for about 20 min. The upper hose got hot pretty quickly...too hot to touch, but it did have pressure. The lower hose remained cool enough to hold, and was softer to the squeeze. After some looking around I found a thermostat sitting in the rain-tray, but didn't get to check if there was one in the engine (the rain caught me). The gauge temp never rose past halfway; the cooling fans never came on. They do however work, I've seen them come on before.

      That's where it is as of right now


    12. 05-21-2005 06:36 AM #12
      STEP 1: remove the small hose from your coolant reservoir, hold it over the opening of the coolant jar. With the engine running, you should have flow. No flow= bad water pump or a restriction in the system. Yes flow= step 2.

      STEP 2: In the morning, engine cold... take the cap off, start the engine. If coolant immediately rushes out of the bottle, you've got yourself combustion gases in the CS... bad head gasket, basically. If this doesn't happen, go to step 3.

      STEP 3: Verify your heater blows hot air when at operating temp. Then, engage the A/C and put your hand downstream of the air that the cooling fans are blowing. Does it feel hot like the heater, or cool? If it's cool, put a thermostat in it. And while you're there, replace the housing and also the crossover pipe. They'll eventually break.


    13. 05-21-2005 06:38 AM #13
      One more thing...

      The cap o-ring, if not seated properly or defective, WILL cause boil over. If the car does not exhibit any abnormal symptoms as listed above, try a cap o-ring. Good luck!


    14. 05-21-2005 11:37 PM #14
      I haven't tried anything yet...but the previous owner has bypassed the heater core so i won't get heat inside the car at all. When I engage the A/C, the fans come on so i'll try your steps and i'll post the results.
      Thanks

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