Coolant Header Tank
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HT4100 4.1, 4.5, 4.9 Discussion, Coolant Header Tank in Cadillac Engine Technical Discussion; At what level is yours when cold and when hot?...
  1. #1
    Ruud is offline Cadillac Owners Fanatic
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    Coolant Header Tank

    At what level is yours when cold and when hot?

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  3. #2
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Full when cold, don't check when hot unless you want a face full of hot coolant!!

  4. #3
    Ruud is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Quote Originally Posted by daniel58 View Post
    Full when cold, don't check when hot unless you want a face full of hot coolant!!
    Hmm..then I probably need to add quite a bit because there's nothing visible in the tank hot or cold..

  5. #4
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    These call for sealant pellets (OEM), they are cheap from any parts store. You may want to add that as well.

  6. #5
    Ruud is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Quote Originally Posted by daniel58 View Post
    These call for sealant pellets (OEM), they are cheap from any parts store. You may want to add that as well.
    Thanks for that. Unfortunately not available in the UK. I've found a pack of 6 GM tabs on Ebay US for $13.99
    Is it possible to use a different leak sealer like K-seal?

  7. #6
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Probably would be ok to use an alternative, but Cadillac recommends the seal tabs. Really the best thing would be to find the leak and repair it. Check the side tanks on the radiator and the front cover/ waterpump area. If you have an internal leak (head gaskets) you have big trouble. Check for coolant in the oil or bubbles in the coolant cold of course. Also these have a metal pipe that runs under the eng that rusts out which you can replace with heater hose.

  8. #7
    Ruud is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Quote Originally Posted by daniel58 View Post
    Probably would be ok to use an alternative, but Cadillac recommends the seal tabs. Really the best thing would be to find the leak and repair it. Check the side tanks on the radiator and the front cover/ waterpump area. If you have an internal leak (head gaskets) you have big trouble. Check for coolant in the oil or bubbles in the coolant cold of course. Also these have a metal pipe that runs under the eng that rusts out which you can replace with heater hose.
    Thanks Daniel,

    I have no bubbles in the coolant or an oily coolant, the oil looks normal and not milky at all. The only thing that I could find is a white/tan foamish stuff under the oil filler cap. This can be there due the engine runnung for short periods only. The car is not on the road yet so I guess after a good blast down the motorway it should clear up. There is no sign of external leaks either.

  9. #8
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    Those are good signs that the eng is ok, but the lost coolant had to go somewhere. I have had situations where the leak would not show up unless the car was working hard on the highway, hard to see then. You may try blocking the front of the car, cardboard or somethng. Monitor the temp with the on board diagnostics while doing this. The plastic end tanks on the rad would be a good place to watch. Could be somethnig easy like the radiator cap is weak.

  10. #9
    Ruud is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    1 thing puzzles me though. The overflow tank is at atmospheric pressure so always lower or equal to the pressure in the system. How can coolant from the overflow tank get in the system?

  11. #10
    daniel58 is offline Cadillac Owners Fanatic
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    Re: Coolant Header Tank

    The coolant from the overflow tank gets drawn back into the rad as the rad coolant cools (contracts) through the small hose connected just below the cap. Problem areas here are to make sure the hose is in good shape and have good rad cap. Radiator caps are cheap and should be replaced every 2 years or so when you do your regular coolant change.

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