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  1. #1
    Join Date
    Dec 2008
    Location
    Bourne, MA, USA
    Posts
    307

    Default cooling system pressure check

    Other than checking the cylinder compression (on another thread) I am also testing the cooling system for a possible leak. I got a loaner Stant style pressure tester from Autozone and then checked online for directions on how to use. (http://ww2.stant.com/repository/docu...1164_20091.pdf) When I tested the 7# psi caps, the caps from both 8.1L engines would prevent any higher pressure than about 7# but neither one would hold any amount of pressure. The online tester directions indicate that the caps should hold pressure which makes sense to me. I purchased an automotive radiator cap and it would hold pressure while preventing pressure above 7#. Are marine heat exchanger caps different that automotive (other than cost which is normal for anything to do with boats)?

    Another test is to connect the tester and start the engine and observe the pressure. One engine does show pressure slowly building up to about 7-8 lbs but the suspect engine does not. However if a pump the tester up to about 8-10 lbs it will hold pressure both with the engine running or with it shut down. So it "appears" to be holding pressure OK and I don't know now if the recent loss in coolant may just have been due to an air pocket in the system which finally cleared.

    Ideas and suggestions please.

    Erich

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    6,765

    Default Re: cooling system pressure check

    I didn't check your link but the Stant documents I've found in the past are excellent at explaining the hows and whys with closed cooling.

    If the cap isn't holding pressure, check its gaskets...long term compression could deform them and cause a "failure" when testing.

    The design is common between auto and marine; some of the materials change (on the better caps) to retard the effects of corrosion. As long as the correct design is selected, the caps will usually interchange as the auto standards are typically used.

    If you connect the pressure tester and start the engine, the pressure in the closed system will rise as the coolant heats up...using the "good" engine for a baseline is a reasonable approach...some vriation between them is likely but not much.

    As far as compression testing goes, GM redefined their official procedure almost 15 years ago. I posted it a while back but can't tell you when. If a search doesn't locate it, and you want it, send a PM with the email you want it sent to and i'll get to it as time permits.

  3. #3
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    9,092

    Default Re: cooling system pressure check

    You say that you've had a recent loss in coolant.
    Do your H/E's have recovery systems?
    If so, the recovery systems must have no suction leaks to/from the reserviors... and must have the correct pressure caps for a recovery system.
    IOW, they must seal at the inner pressure release side, but also seal at the upper area for the suction coolant return to work upon cool-down.

    You can also purchase test strips to detect the presence of hydrocarbons within the ethylene glycol side of the system.


    .
    Last edited by RicardoMarine; 07-29-2014 at 06:14 PM.
    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  4. #4
    Join Date
    Dec 2008
    Location
    Bourne, MA, USA
    Posts
    307

    Default Re: cooling system pressure check

    Quote Originally Posted by RicardoMarine View Post
    You say that you've had a recent loss in coolant.
    Do your H/E's have recovery systems?
    If so, the recovery systems must have no suction leaks to/from the reserviors... and must have the correct pressure caps for a recovery system.
    IOW, they must seal at the inner pressure release side, but also seal at the upper area for the suction coolant return to work upon cool-down.

    You can also purchase test strips to detect the presence of hydrocarbons within the ethylene glycol side of the system. .
    Yes the system has a recovery system. I recently went on a 4 hr cruise and I believe the overflow/recovery container was about half full and therefore I assume the HX and closed system was full also. A day of two later I was checking oil and antifreeze and saw that the recovery container for the port engine was empty. The stbd tank was 1/2 full as it was before the trip. The HX took about a quart and another quart or so went into the recovery tank. This loss of coolant is what prompted me to get a pressure tester to check the system. So I believe that part of the system is working OK. I am getting a new HX cap tomorrow. Today on a cold port engine I pumped the system up to 10 lbs and 3 hours later it was still at 10 lbs. So I will try running with a new cap and watch it closely for coolant level/loss.

    Why would I test for hydrocarbons and what does that mean if the antifreeze has them in it? Where can these test strips be purchased?

    Thanks,
    Erich
    Last edited by erich; 07-30-2014 at 09:04 PM.

  5. #5

    Default Re: cooling system pressure check

    Sorry. I replied to wrong thread!
    Last edited by Okiedokie; 07-18-2017 at 09:18 AM.

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