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  • Low compression

    Hi all,

    My v6 has just hit 250000ks and during the service I decided to do a compression test finding that 2 of the cylinders have lower compression around 170psi and the others are all 210, ran the test twice to verify with the same results, squirted a bit of oil in the cylinder and came up to 250psi,
    Should I be expecting lower compression at this mileage, the car runs fine doesnt use much oil between services, temp always spot on and no strange noises,

    Not really sure what the options are, any pointers would be great,

    thanks in advance!

  • #2
    its interesting that there is a difference , to this point , i dont know what margin is acceptable , a 10% difference i have heard before , but good boat mechanics work with no less than 5% difference.
    so if the highs are 210 you should have the rest no less than 189 , if its 10 % ... what difference would really be acceptable or sota normal . i havent checked mine , maybe one day soon i may , i have 270 on the clock.so i could imagine similar results.

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    • #3
      I thought that number looked high so I checked, admittedly only from a Gregory's manual.
      It says 190 psi upper reading with a low limit of 145 psi and 15 psi difference max to min readings.
      Compression tests are not always accurate, but those numbers seem well high.
      That variation between readings isn't great and could be investigated further via a leak down test.
      Did the plugs from all cylinders look similar, no obvious oily ones or such.
      Considering the K's and that you're happy with performance, oil and water usage etc I can't see the need for more checks.

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      • #4
        I have one at 167psi, 4 in the high 170's or low 180s and one at 192psi. 175,000kms. Seems fine. I am going to keep an eye on it.
        2007 120 Series GXL V6 Manual Black
        JTG Liquid LPG, Pacmaker Extractors, Redarc Dual battery system, 120W Solar Panel, Rino HD roof rack, Iron Man Awnings and Roof Top Tent, External LED Lighting, Longeranger 22L Water Tank, Black Widow half barrier, more to come...

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        • #5
          Those readings stooy would leave you with a 25 psi more or less variant and also a bit over 10 %....and well within the Gregory"s manual listing. . It would seem that you are good .I will try mine today and update this post . It will i think, be interesting, to see if i also fall in line with your reading.

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          • #6
            Did my pressure test but found quite a different lot of psi readings . also i knew that i have a slight rocket cover leak , but i didnt realize i had oil leaking also in the spark plug chamber , so readings are with a grain of salt cuz a number of them had oil fall into the chamber after pulling out the plugs, but here are the readings that i got ,,

            drivers side 195/205/218
            passenger side 216/210205

            all fairly high readings , but i will have to wait to repair those oil leaks and pressure test again in the future when those piston chambers are clear of oil dripping in and messing up readings.

            i'm wondering if that is why there are readings that seem a bit unbalanced from the other posts , if there was oil on the thread of the spark plug that was taken out , then oil dripped into the piston chamber /bore before you had a chance to pressure it ... reading will be incorrect.....

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            • #7
              Hi All,

              Sorry for not responding earlier its been a busy time for me!
              Thanks for the info, all plugs look healthy a nice grey colour, that coupled with it not using oil between services makes me think I shouldnt worry too much, I plan on keeping the car for another year or so and will keep an eye on compression every second service from now on.
              My compression tester might be inacurrate and showing high readins but ran the twest twice with consistent results so more of a comparison between cylinders more than anything,

              All the best!

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