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Thread: air bubbles in the coolant

  1. #1

    air bubbles in the coolant

    I have a 2000 Forester with 270K miles. It runs fine.. no issues and no bad or steamy exhaust.


    I just replaced the radiator. At that project I also replace the top and bottom radiator hoses , the radiator thermostat and put a new gasket on the water pump. I also put in a new radiator cap.

    It seems that I did what I've always done on old US cars for the last 20 years.


    So, Now the Subaru is having an odd issue.

    The overflow tank gets full after a drive and there are air bubbles also coming out too into the reservoir.


    When the engine has sat for an hour and cools off... I take the cap off and look inside the radiator. The fluid is low because I can see the aluminum on the inside.

    The next part is I start the engine with the cap off and add a little fluid and let the engine run and watch the radiator fluid.

    I add a little more fluid to basically fill the radiator.

    At this point with the cap off and engine running I can see air bubbles being pushed through the top hose because the air bubbles come over to the opened cap hole ... The temp gauge is showing normal temp as it points to the middle of the gauge...no over heating or under cooling.


    There is no oil in the radiator fluid and the engine oil is not foamy... and the trans oil is normal... no issues. Plus the heater is under the dash and it works and is not leaking.

    I can't figure out where the air bubble are coming from and what to do to make it stop.

    Am I missing something?


    Thanks

  2. #2
    Super Moderator Justin 05 Sti's Avatar
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    Sounds like a very mild case of blown head gasket(s). It is a pretty common problem.

  3. #3
    Scoobie Expert BigC's Avatar
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    If you don't have any cross contamination, a leak down test would be next if you wanted to throw money at the problem. If this has been going on a while...you could pull the spark plugs and check to see if they all look the same. Typically a leaking cylinder will run cooler than the others and reflect that in the color of the plug. The fact that it's not overheating is somewhat disconcerting although as Justin eluded to, it may be early in the head gasket failure phase. I have some parts lying about from an '01 Forester (except a motor) if you need something to troubleshoot with.
    -Brent

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  4. #4

    maybe I'm stupid

    Quote Originally Posted by BigC View Post
    If you don't have any cross contamination, a leak down test would be next if you wanted to throw money at the problem. If this has been going on a while...you could pull the spark plugs and check to see if they all look the same. Typically a leaking cylinder will run cooler than the others and reflect that in the color of the plug. The fact that it's not overheating is somewhat disconcerting although as Justin eluded to, it may be early in the head gasket failure phase. I have some parts lying about from an '01 Forester (except a motor) if you need something to troubleshoot with.

    I did the exhaust air in the radiator test with a too (combustion leak tester) l rented from O'Reilly's . I still get bubbles but the test water doesn't turn yellow and the therm temp doesn't change..

    Maybe I'm a moron... No idea.

    Unless I or someone else comes up with another idea that finds what is causing the air bubbles... I'm just going to drive the car in town until it passes away and I'll just walk away form it.

    I wish we could find what is causing this issue... or if it is really an issue.

  5. #5

    cylinder pressure

    I pulled the plugs and they all look the same...they are a few months old and they are all the same lite color... none are black or brown... they are light white.


    next I'll measure the cylinder pressure with a pressure gauge that I have and have used many years on other cars.

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