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How to do a compression test on your engine

Cooley shows you how to do the king of all engine tests.

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  • hellcat1988
    April 12, 2017

    While I applaud you for showing this, there are a few things that you left out.

    Also, you can use a remote starter like the one shown on almost any engine with an electric starter. Many are connected to full battery power 100% of the time and that button only bridges power to the signal connection, which is the same kind of signal it would get from the ignition of the car when you turn the key.

    The only real difference for more modern cars with a typical starter design is that instead of a ring terminal and bolt holding the signal wire on, it's usually some form of spade connector.

  • thejeffinvade
    April 12, 2017

    That is a ford demo engine

  • Will
    April 12, 2017

    Loving the more cooley vids!

  • roguedogx
    April 12, 2017

    for the third kind of compression loss, smell the oil. if it smells like a marina, you've got work to do. that or grab your drink of choice and call your mechanic, trust me you'll need the drink.

  • jose
    April 12, 2017

    awesome one on one

  • Bill Wilmington
    April 12, 2017

    Did one last week lol

  • FastLikeUNO
    April 12, 2017

    Excellent video Brian!

  • Nick Stern
    April 12, 2017

    Cooley Nails it again!

  • Oshane Williamson
    April 12, 2017

    Well done Cooley

  • anonymous parrot
    April 13, 2017

    great vid

  • Fernando Sosa
    July 11, 2017

    I think you forgot to mention about opening throttle body on newer cars and trying to do it with a warm car… allowing the metals to expand to closer to operating temps.

  • Jesus Moya
    July 15, 2017

    if I take out all the spark plugs start from cylinder 1 2 3 4 on my 91 Honda CRX without disconnecting anything else like the ignition system or pulling out fuel relay just taking out the spark plugs will I get an accurate reading?

  • B T
    October 17, 2017

    excellant video please don't delete it

  • S54
    December 2, 2017

    Great video. I done my first compression test today. I got 137 132 129 141psi. Then i done it again and got 131 131 131 130psi. Which would be the most accurate. Thanks!

  • Jaskanwar Randhawa
    March 8, 2018

    just hold the gas padle all the way to the floor no spark fuel will be sent to the engine anything newer then . 2000 you can try it in your car it will not hurt any thing it will just crank

  • Lennox
    May 8, 2018

    Hi , i think there is no need to remove the fuse for the Ignition , because i have to crank the
    engine using the ignition , right ?

    One more thing is that to Crank the engine it might discharge the Battery even if the battery is new
    so what should we do to avoid discharging the battery while doing compression test for all the
    cylinders ? thanks ..

  • J R
    June 10, 2018

    Great how to perfect explanation and I was watching a TV show and trying to explain they should do this before doing what they're doing by replacing a top end on a engine but they didn't do a leak down test 1st and they just put new heads with a cam and intake, sad because 1 piston can be junk on compression, will find out the hard way. Its an old 70's truck that you know had been pushed. Oh well, who am I, just a TV watcher, mechanics on tv shows should show or tell reasons why their aren't doing it. The sad part is its a customer's vehicle that gets done but not right all the time.

  • VSW
    September 4, 2018

    Is the running of the engine up to standard running temperature before commencing the test advisable?

  • Stephen Brennan
    June 12, 2019

    Outstanding hosting. Nice production quality too.

  • Richard 77
    June 19, 2019

    I thought you needed to remove all plugs and connect the battery to a booster pack

  • Raymond Oflaherty
    July 5, 2019


  • better soc
    August 25, 2019

    thank you, good tutorial

  • Jo t
    August 26, 2019

    About how much oil to squirt in a cylinder ?

  • Blind River Bill
    September 3, 2019

    take out ALL the plugs, hold the throttle wide open, and you should wear a tuxedo (WTF with the street clothes?)

  • truth tellor
    September 3, 2019

    Rented Oreillys tester… got zero psi on all cylinders, drove back and went somwhere else on zero psi car….

  • J Garced
    September 7, 2019

    I did my first test on my Honda Ridgeline, but I think they are too high, 235 225 225 220 230 230, is that good???, I took out all the spark plugs, fuel pump relay, ignition fuse, ignition coils etc.

  • Pro Joe
    September 15, 2019

    Short and sweet, nothing but the information i wanted and needed, thanks.

  • Lisa T
    February 24, 2020

    hmmm you begin by saying" if you are even remotely mechanically inclined" …. Not sure if I even quality for that much. I do want to learn though.

  • Monir Obaid
    March 22, 2020

    so if the pistons are bad and leak oil it will read high compression ? because already has its own oil

  • Budget Boost DIY
    March 26, 2020

    My FSM wants me to get engine to normal operating temos before I do the compression test,I read NOT to remove spark plugs from hot engine so I was considering removing them while engine is still cold then just snugging them down about 1-2ft lbs or just hand tight using the enter of the rachet for less leverage and THEN warming up the car.

    Would this be the most ideal way to do this?My only concern is blowing out the spark plug or something but maybe that cant happen?

  • Shajahan shajahan
    May 28, 2020

    you could have done this video much more simple,and better!

  • CrociatoAzzurro
    June 8, 2020

    I forgot to disable fuel when I did one today.

  • manu Sankar
    June 28, 2020

    Sir I have a doubt.
    If the piston rings are damaged is it possible to burn engine oil already in engine .

    If it's happen the engine oil thus entered will act as a seal and will shows the compution pressure reading
    That will show when we pour some oil in it for sealing

  • Andrew Dean
    July 11, 2020

    If you're doing a compression test and it takes 20 compression Strokes to get up the maximum pressure on your compression gauge, does that indicate worn piston rings?

  • Umanng Mittal
    July 12, 2020

    So concise yet covered everything. No blabbing, you know your stuff. I like it!

  • Bdan6999
    July 18, 2020

    How do you resolve the issue if there is no compression in one of the spark plug slots? I have a 2009 Toyota Passo which uses 3 spark plugs. The middle one has no compression. My mechanic suggested that I change the entire engine. Is there a cheaper alternative?

  • Piri Hern
    August 10, 2020

    Muy bueno gracias

  • Glenn Rae
    August 27, 2020

    Brilliant cheers

  • mokhtar traples
    September 18, 2020

    One like for new information that i lrean from you thanks

  • Jean Philippe GUERRE
    September 20, 2020

    Warm engine, healthy battery, all spark plugs removed and wide open throttle during cranking are both required to perform a real accurate test to me.

  • MihalyMusic
    October 23, 2020

    Straight forward. No bs. Thanks

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