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High Pressure in the Coolant Expansion Tank

Discussion in 'Technical Discussion' started by T.K., Aug 24, 2014.

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  1. T.K.

    T.K. Senior Member

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    Gentlemen, I am experiencing high pressure (1.8 bar) and some coolant loss in the expansion tank. It only occurs at high engine rpm.

    Are there any other causes apart from a failing cylinder head gasket and exhaust gases escaping into the coolant system? Can tightening the cylinder head bolts a quarter turn solve the problem assuming the gasket is not damaged?
  2. 993RSR

    993RSR Senior Member

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    Try posting that question on boatdiesel.com. Forums specific to your engine. Very helpful
  3. K1W1

    K1W1 Senior Member

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    Hi,

    What temp is the coolant getting to when you have this problem and do you re fill the expansion tank everytime you use the boat?
  4. T.K.

    T.K. Senior Member

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    No increase in coolant temperature. It remains at 85 degc. Correct, the expansion tank needs to be topped up with approx. 4 liters of coolant each time the boat is used.
  5. Marmot

    Marmot Senior Member

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    Let's start the troubleshooting in an orderly manner.

    For a start ...

    What make and model of engine? (Is it a MaN that requires jacket water pressurization?)

    Where are you measuring coolant pressure?

    Is the coolant expansion tank overflowing so the loss occurs at that point or is it vanishing someplace else?

    Have you tested the coolant for combustion gases?

    Have you used a tracer dye test to look for coolant leaks?
  6. K1W1

    K1W1 Senior Member

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    Hi,

    If you don't top up the expansion tank how much comes out next time you run it?
  7. Capt Ralph

    Capt Ralph Senior Member

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    Is there a recovery bottle? Is the cap of correct type?
    Lots of minds here to help, we need some more info.
  8. Capt J

    Capt J Senior Member

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    No, the head bolts cannot be tightened solve the problem, as the head gasket would already be damaged if you're experiencing a loss of coolant through it. I'll wait till you respond with the info everyone is asking for before answering more. You could also be losing coolant in other places also, heat exchanger, aftercooler, etc.
  9. T.K.

    T.K. Senior Member

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    - Volvo Penta D6-435
    - Coolant pressure is measured by means of a pressure gauge fitted instead of the expenasion tank cap.
    - Coolant is lost through the expansion tank cap.
    - No. How is that performed?
    - No.

    Thank you all for your help.
  10. K1W1

    K1W1 Senior Member

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    Please see my replies inserted into the quote
  11. Marmot

    Marmot Senior Member

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    Tracer dyes glow brightly under UV light. That makes it very easy to find leaks from systems which have it added. Your existing coolant may or may not already flouresce but a tracer dye removes all doubt as to the source.

    But, if as you say the loss is through the cap, make sure the right cap is installed and is working properly. If the expansion tank is pressed up when cool and the cap is installed then normal expansion will blow a lot out and create considerable pressure.

    Do you have a recovery tank installed? Is the expansion tank cap the right kind for use with a recovery tank?
  12. T.K.

    T.K. Senior Member

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    Thanks, I have found the leak detection kit and purchased one.

    Best regards, T.
  13. T.K.

    T.K. Senior Member

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    The cap is the correct part, I have even replaced it when the problem first occured.

    I have measured the pressure at the cap using a pressure gauge and it measured 1.8 bar with a running engine at operating temperature when it should not exceed 1 bar.
  14. Marmot

    Marmot Senior Member

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    When you refill the tank do you fill it completely to the edge of the cap?

    What is the pressure rating marked on the cap itself?

    K1W1 asked: "If you don't top up the expansion tank how much comes out next time you run it?"

    That is a very important question because if you don't lose any more and the pressure does not exceed the cap rating then you may be overfilling it.

    What happens after the 4 liters gets blown out? Does more coolant keep flowing? Do you get "steam" or vapor? Does the pressure drop? Does the engine temperature increase?
  15. karo1776

    karo1776 Senior Member

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    Couple Suggestions from an amateur!

    I don't know what you have for engine coolant but I am assuming it is not raw water... ! OK enough joking.

    Check the exhaust for a different smell usually leaks that are serious show up that way... now don't know what coolant you are using so that may not work. Its a real rough guide but if you smell coolant in the exhaust you are in deep merde!

    Back to minor leak checking suggestions.
    While engine is cold fit a pressure adapter to the coolant expansion tank or the cap... use a regulated source of compressed air to pressurize to the correct running pressure. What to use well you can adapt a engine leak down tester and use it but if you know how to use that don't accept any leak down rate! But IMPORTANTLY... If the coolant goes down in the tank... you gotta leak. Now it will go down at first a little because of hose expansion and the like but it will stop quickly. If it keeps going down that is the key.

    First place I would check is the heat exchanger to raw water... or any other heat exchanger. You might need to remove the cover to get access to the inside. Now if you have a sonic leak tester you can use that to find the leak... this works better if the coolant has been drained but will work without draining. This is a microphone that picks up the sound of leaks... one like they use to check vacuum bag leaks in composite manufacture... you wonder how the boat builders find the leaks in the vacuum bags... that is how. The sound is different with water than an air filled system. I learned when I involved with race cars... the coolant systems would be pressure checked before filling with coolant and the ultrasonic leak test done with air... .

    If you cannot find the leak then you warm the thing up to operating temp. and then shut down and do the pressure leak testing. But try cold first as it is easier to check around a cool engine than a hot engine.
  16. weto

    weto Senior Member

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    I have one question, Why is dbltime trying to refer OP to another website ?
    :confused:
  17. K1W1

    K1W1 Senior Member

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    Probably because he/she can
  18. T.K.

    T.K. Senior Member

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    Gentlemen, the leak is one way only. The pressure in the expansion tank increases to 1.8 bar with the engine running at operating temperature and only at very high rpm. The pressure in the expansion tank does not decrease if the engine is slowed down or even if it is stopped. It remains at 1.8 bar with the engine switched off until it is manually bled and the pressure gauge removed to replace the cap. This means that there is no coolant leak into the chambers or into any other part of the engine. The pressure is only forced into the cooling system but is not allowed back.
  19. karo1776

    karo1776 Senior Member

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    Thanks for the reminder. The tragedy of man is he forgets.

    A few questions are in order...

    What make / brand of engine, year, model, how many engine hours, and what is the engine condition details would help the experts here?

    Predominately do you do your own service... have a hired engineer or captain doing it... or do you use the manufacturers service ?

    What is the coolant temperature verses power, and where is this measured?

    What specification does the manufacturer have for coolant temperature ?

    Now to be clear... the pressure is what at normal cruise?

    At high power... the pressure goes up to 1.8 bar and then stays there!

    What happens to coolant level at startup to warmed up and operating at normal cruise?

    What happens to coolant level from warmed up operating at normal cruise to the high power output conditions?

    Can you estimate if and how much coolant loss there is... may be none! This last question seems not to apply but just checking.
  20. Marmot

    Marmot Senior Member

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    One last attempt ...

    What happens after the initial 4 or 5 liters are expelled through the cap?

    Is the loss ever more than that amount?

    Do you fill the expansion tank to the brim before closing the cap?

    There is a reason that tank is called an "expansion tank."

    You are not helping much by not providing answers to the questions that probably hold the answer.

    As an aside, if you are filling the tank to the brim then putting the cap on, you have to expect the coolant to be lost as it expands. If you replace the venting cap with a closed cap and gauge, the expanding coolant can reach very high pressure very quickly. You are lucky it hasn't caused damage to the system elsewhere.

    In normal operation, the coolant pressure should not exceed the pressure rating marked on the cap - you never answered that question either - and if the expansion tank is overfilled it will expel enough water to relieve the pressure above the marked maximum pressure then go no higher unless there are combustion leaks or a high temperature condition.

    If coolant is normal or low (which implies an air space in the X tank) and you have 1.8 bar pressure the coolant temperature has to be around 130*C so if it stays at 85 you need to reconsider the story, your test methods, or your temperature monitoring equipment.