I learned this in school but you explained it 10x better plus you dropped a diag jewel when you explained what the results of a wet compression test vs cranking compression test could mean.
There should be a Schrader valve (like the valve stem on your tire) in the hose. Someone (probably whoever rented it last) likely removed it. Without that valve, any pressure the engine builds will be gone as soon as the valves open, and you'll get a zero reading.
Sometimes it happens that the previous renter didnt report an issue with the tool, to avoid getting charged for it. That happened to me with a torque wrench at autozone. I went back and mentioned the issue and they gave me another that worked fine.
excellent video. i knew nothing about how to do this test, now thanks to you i know how to do it and alot more detail as well; like what could be causing low compression in cylinders. thanks for not talking sooo fast, like most others..and speaking clearly and to the point without a lot of unwanted music, drama etc. ..yoour an excellent teacher..actually a professor.
Absolutely excellent video. All information was incredibly useful and concise. It’s exactly what I needed. Only thing is I have a mechanical fuel pump, so removing a fuse won’t work on that one. Anyway, you have a new subscriber, as you are a great teacher
Looking at other RUclips videos some of them say you make sure the enginer is warmed up before you do this test. That seems like sound advice as metal expands when warmer so it seems sense that it could effect compression.
Absolutely perfect, exactly the information I needed! I'm trying to figure out the cause of low compression on one cylinder, and am hoping it's just in need of a valve adjustment (common for the engine). If I can go get a $50 compression tester and use the oil trick to determine piston rings or valves...would be...just...amazing. I suppose it wouldn't tell me if the valves are wasted or just out of spec, though. Still, thank you!
I'am Your Newest Subscriber Great Videos . I Have A 95 S10 2.2 Liter With 5 Speed Manual Has Choptop Roof Hasent Ran In 11 Years I Wanta Get It Running Again Has Low Compression In A Few Cylinders
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.
There's two schools there. If you warm the engine first, letting things have a chance to seal up, you're getting a reading at operation, yes but, if you do the test cold, you actually can find out what's worn or wearing. I want to know if the rings are just starting to wear or the valves are carboned up and need to be "blasted." Doing it with a hot engine just tends to mask the problems you're trying to find. I'm an ASE engine performance and drivability tech and I came up in the old school world of actually finding any mechanical issues rather than try to cover them up. An engine always gives up its secrets and runs the worst when it's cold... And that's when you find out what lays ahead. :)
Hi, Great Video. Question.?. I own a 1970 Chevy Impala with a 350engine. How do I stop the fuel from going into the carburetor.????. And I also have a HEI Distributor. Can you please let me know how.🙏🏽☹️
Disconnect the fuel inlet from carb, put a tube on it and put the other end into a portable gas tank (so you save that gas) As far as your distributor, disconnect the connector that leads into the HEI. This prevents any spark from being created.
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.
So if I stop the fuel and spark it should be okay to remove the exhaust manifold to get to those back three spark plugs when I'm doing this test, right? Cheers & thanks.
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.
You are 100% correct. Always remove all the plugs, have a good battery to crank the motor and have your throttle wide open. Maybe Cooley thinks he knows, but doesn't really know.
@@jonhromeo6108 To me the most accurate way on a carbureted engine is simply to remove the carb intself. But as it may be a pain to do, unplug the the pump intake line fist. Then let the engine die. After that you can perform the test. Be sure that you maintain WOT and also that the cold start device would'nt mask the carb air intake during cranking operations. Best result if you remove the air filter. Cheers
Vaporised gas, can disturb results as gasoline has a tendency to wash the cylinder liners oil compound when no ignition occurs. Results may vary between a dry or a wet cylinder.
Dylan, If you have a rubber hose somewhere ( AFTER THE PUMP ) crimp it off with vice grips & rubber hose over the teeth. Or disconnect the steel fuel line ( AFTER THE PUMP ) & add rubber hose to it ( WITH HOSE CLAMP ) then run it into a bucket.
To calculate the compression pressure you need to multiple the compression ratio by atmospheric pressure then add the atmospheric pressure to your multiplied result eg if you have a compression ratio of 9 to 1 and a atmospheric pressure of 14.7, 9x14.7 =132.3 +14.7 =147 psi , also I would look up how to carry out a compression test properly
What if the compression drops? Or does that matter? Mine read good at 150 but dropped very slowly like almost not noticeable. But did drop after a while
Please explain more my brother!! My compression was a lot higher but all consistent with each other just after 5 compression strokes. And after the test The 5.2 will not start now. Did I f^__ something up.l disconnectied coil to safe place but not fuel?? Lost here my friend!! Montana Rick.
My car stopped when driving I think my timing belt slipped. My friend tried to push start it. Now it's reading no compression . Would push starting damage the valves?
Im scared.. I just bought an Engine, chasing a P0300 code. A friend said to do a compression test, but I'm scared to do it & find out if there is something internally damaged.
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?
The reading is accurate for that test condition. BUT please be AWARE that leaving the plugs out with everything else connected. Will mean the injectors squirting fuel, the pistons pushing that spray out of the engine in the mist of spark plugs doing what they do best, putting out a spark. With that in mind remember that gas spray and spark is usually a dangerous combination... ;-)
I would also open up the throttle body vanes to allow airflow into the engine. Make sure to undo this step before you put everything back together again and run it for real otherwise you won't be happy.
ok but using the compression tester you are using with no Shrader valve at the plug end will give you a incorrect reading as you are not correct in the swept volume of the cylinder. best compression tester is cp7828 with the scrader valve. .you will get low compression on that unit.
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
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.
I found alot of cars after the 1998 model year can still have their immobiliser kick in and cut power to everything except the ignition switch which then requires the key to be inserted and turned to the reds while metal contacts touch to reset the immobiliser My cars are some of them
@@ESISTTIGER You must have some pretty special cars then, because every vehicle I've ever worked on here in the US has worked fine with bridging the starter solenoid without the ignition key in or on.
@@hellcat1988 factory GM 1998 onward anti-theft in Australia is great only 2 ways too even crank the car 1 have the actual key 2 swap out the BCM, ECU, Steering column with a different barrel and a key too match which takes ages Anything else cuts power
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.
![How To Perform a Compression Test - [EASY]](http://i.ytimg.com/vi/3VmmL0YAO14/mqdefault.jpg)
![How To Perform a Compression Test - [EASY]](/img/tr.png)
Short and sweet, nothing but the information i wanted and needed, thanks.
So concise yet covered everything. No blabbing, you know your stuff. I like it!
I learned this in school but you explained it 10x better plus you dropped a diag jewel when you explained what the results of a wet compression test vs cranking compression test could mean.
Rented Oreillys tester... got zero psi on all cylinders, drove back and went somwhere else on zero psi car....
I was about to go and rent the tool from them too lol thats why I was watching this video. guess I'm not going to anymore
There should be a Schrader valve (like the valve stem on your tire) in the hose. Someone (probably whoever rented it last) likely removed it. Without that valve, any pressure the engine builds will be gone as soon as the valves open, and you'll get a zero reading.
Sometimes it happens that the previous renter didnt report an issue with the tool, to avoid getting charged for it. That happened to me with a torque wrench at autozone. I went back and mentioned the issue and they gave me another that worked fine.
Couldn’t have been user error!! 😂
Tool was obviously broken
OMG so quick and well spoken with no babble... THANK YOU :)
Exactly the style of information delivery we need more of.
excellent video. i knew nothing about how to do this test, now thanks to you i know how to do it and alot more detail as well; like what could be causing low compression in cylinders. thanks for not talking sooo fast, like most others..and speaking clearly and to the point without a lot of unwanted music, drama etc. ..yoour an excellent teacher..actually a professor.
Outstanding little video. Great way to introduce someone to compression testing basics…..
I'm so pleased that you spoke about the 'wet' compression test. So many 'experts' don't know about that one.
Straight to the point. Exactly what I was looking for
Great information, and great production and editing. Thanks for keeping it concise!
Outstanding hosting. Nice production quality too.
Absolutely excellent video. All information was incredibly useful and concise. It’s exactly what I needed. Only thing is I have a mechanical fuel pump, so removing a fuse won’t work on that one. Anyway, you have a new subscriber, as you are a great teacher
Thank you for this very simple and clear explanation of compression testing
I’m high and happy…
not me.. my car is misfiring and thats why im here.
@@lilgagey3889😢
Looking at other RUclips videos some of them say you make sure the enginer is warmed up before you do this test. That seems like sound advice as metal expands when warmer so it seems sense that it could effect compression.
Absolutely perfect, exactly the information I needed! I'm trying to figure out the cause of low compression on one cylinder, and am hoping it's just in need of a valve adjustment (common for the engine). If I can go get a $50 compression tester and use the oil trick to determine piston rings or valves...would be...just...amazing. I suppose it wouldn't tell me if the valves are wasted or just out of spec, though. Still, thank you!
Clearest information and tutorial. Just what I needed
Excellent excellent video; great communication skills too; very informative !!!!!!!
I'am Your Newest Subscriber Great Videos . I Have A 95 S10 2.2 Liter With 5 Speed Manual Has Choptop Roof Hasent Ran In 11 Years I Wanta Get It Running Again Has Low Compression In A Few Cylinders
Top notch professional tutorial!
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.
There's two schools there. If you warm the engine first, letting things have a chance to seal up, you're getting a reading at operation, yes but, if you do the test cold, you actually can find out what's worn or wearing. I want to know if the rings are just starting to wear or the valves are carboned up and need to be "blasted."
Doing it with a hot engine just tends to mask the problems you're trying to find. I'm an ASE engine performance and drivability tech and I came up in the old school world of actually finding any mechanical issues rather than try to cover them up. An engine always gives up its secrets and runs the worst when it's cold... And that's when you find out what lays ahead. :)
Pressure test should be done on cold engines.
Excellent video Brian!
On newer cars (ie after 1990) you can generally hold the accelerator and turn the key rather than disconnecting fuel and coils
why holding the accelerator?
Clear flood mode, prevents car from starting
Cooley Nails it again!
What an excellent video on the subject!
Informative and straight to the point.
Hi, Great Video. Question.?. I own a 1970 Chevy Impala with a 350engine. How do I stop the fuel from going into the carburetor.????. And I also have a HEI Distributor. Can you please let me know how.🙏🏽☹️
Disconnect the fuel inlet from carb, put a tube on it and put the other end into a portable gas tank (so you save that gas)
As far as your distributor, disconnect the connector that leads into the HEI. This prevents any spark from being created.
Cool Thanks 👍
Straight forward. No bs. Thanks
I agree, short and sweet!
Awesome quick video!
"Your engine is all about cylinders"
Me with 13b: I already failed that one
Thanks. Very helpful!
Well done Cooley
Best video so far 😊👍
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.
Boy I should have grabbed the drink before bringing it to my mechanic, that hurt my wallet
@@professionalgenny5096 sorry to hear that.
@@professionalgenny5096 Oof, been there...
Awesome....to the point.....no quirky comments or trying to be funny....
excellant video please don't delete it
Very good and informative video, thank you!
Great video very clear
Loving the more cooley vids!
So if I stop the fuel and spark it should be okay to remove the exhaust manifold to get to those back three spark plugs when I'm doing this test, right? Cheers & thanks.
I hope I don't regret buying one off of Temu, but I'm still learning anyway.
what is a good place to buy a used or rebuilt engine i am in sacramento ca
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.
Good job
Fantastic!! Thank you!
man! very well explained Thank's
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.
You are 100% correct. Always remove all the plugs, have a good battery to crank the motor and have your throttle wide open. Maybe Cooley thinks he knows, but doesn't really know.
@@johnnybonacci7114 CORRECT, both of you, I also put a battery charger on my battery while performing the test. HE DOESN'T REALLY KNOW, LMAO.
On carburated motors do u take off mechanical fuel pump before test ? Or just leaave on and test ?
@@jonhromeo6108 To me the most accurate way on a carbureted engine is simply to remove the carb intself.
But as it may be a pain to do, unplug the the pump intake line fist. Then let the engine die.
After that you can perform the test.
Be sure that you maintain WOT and also that the cold start device would'nt mask the carb air intake during cranking operations.
Best result if you remove the air filter.
Cheers
Vaporised gas, can disturb results as gasoline has a tendency to wash the cylinder liners oil compound when no ignition occurs.
Results may vary between a dry or a wet cylinder.
Novice question. I've got a 68 javelin running a mechanical fuel pump. What is the best way going about shutting off fuel supply? Thanks in advance
Dylan, If you have a rubber hose somewhere ( AFTER THE PUMP ) crimp it off with vice grips & rubber hose over the teeth. Or disconnect the steel fuel line ( AFTER THE PUMP ) & add rubber hose to it ( WITH HOSE CLAMP ) then run it into a bucket.
Please@@NoWr2Run
what should be the compression of the cruze 1.8 petrol engine??
my chevy has 11 bars for each cylinder
To calculate the compression pressure you need to multiple the compression ratio by atmospheric pressure then add the atmospheric pressure to your multiplied result eg if you have a compression ratio of 9 to 1 and a atmospheric pressure of 14.7, 9x14.7 =132.3 +14.7 =147 psi , also I would look up how to carry out a compression test properly
What if the compression drops? Or does that matter? Mine read good at 150 but dropped very slowly like almost not noticeable. But did drop after a while
Perfectly normal.
Do you have to warm the engine up to do it?
Does the engine need to be warm ?
Thanks.
Disabling the spark..is that the same as pulling out the COIL PACK?
Veteran in automotive industry experience
"hope your cylinders are all high and happy!" 🤣
Does 3 in 1 oil work just fine to spray into the cylinder like he mentioned? Or does it have to be motor oil
3 month old comment but it has to be motor oil. You don’t want to contaminate the oil with solvents.
You are right but if the top of the piston has carbon build up it will artificially raise the compression
Please explain more my brother!! My compression was a lot higher but all consistent with each other just after 5 compression strokes. And after the test The 5.2 will not start now. Did I f^__ something up.l disconnectied coil to safe place but not fuel?? Lost here my friend!! Montana Rick.
my toyota corolla 2014 model 1.3 Liter engine compression is 130 psi on each cylinder, is it good or not?
My car stopped when driving I think my timing belt slipped. My friend tried to push start it. Now it's reading no compression . Would push starting damage the valves?
Great vid
awesome one on one
very concise thanks!!!!!
great video :D
so if the pistons are bad and leak oil it will read high compression ? because already has its own oil
Excellent
So how do you cutoff the fuel for an older carbureted vehicle?
So would an engine with 10.5 compression ratio yield higher numbers then an engine with 8.5 ?
Google what your particular engine is supposed to be. My honda is 220 across the board lol
What if i actually kept the fuel pump on and start the engine to measure the pressure, is that ok?
That's ok if you remove the injectors cables, otherwise the catalytic converter won't like it.
The petrol will spray inside cylinder.
Im scared.. I just bought an Engine, chasing a P0300 code. A friend said to do a compression test, but I'm scared to do it & find out if there is something internally damaged.
If its carburated does throttle need to be wide open?
About how much oil to squirt in a cylinder ?
But I love the presentation very much ...no blabbing
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?
The reading is accurate for that test condition. BUT please be AWARE that leaving the plugs out with everything else connected. Will mean the injectors squirting fuel, the pistons pushing that spray out of the engine in the mist of spark plugs doing what they do best, putting out a spark.
With that in mind remember that gas spray and spark is usually a dangerous combination... ;-)
Jesus Moya that will alter your compression reading slightly. Fuel doesn’t compress.
Awesome , thanks
I would also open up the throttle body vanes to allow airflow into the engine. Make sure to undo this step before you put everything back together again and run it for real otherwise you won't be happy.
Warm or cold test? Or doesn't it matter?
Thank you
ok but using the compression tester you are using with no Shrader valve at the plug end will give you a incorrect reading as you are not correct in the swept volume of the cylinder. best compression tester is cp7828 with the scrader valve. .you will get low compression on that unit.
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
thank you!
Thanks homie
Just got a tester got the hood open and realized i left my tools in my buddies broke down van😂💀
What year is this Cougar?
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.
I found alot of cars after the 1998 model year can still have their immobiliser kick in and cut power to everything except the ignition switch which then requires the key to be inserted and turned to the reds while metal contacts touch to reset the immobiliser
My cars are some of them
@@ESISTTIGER You must have some pretty special cars then, because every vehicle I've ever worked on here in the US has worked fine with bridging the starter solenoid without the ignition key in or on.
@@hellcat1988 factory GM 1998 onward anti-theft in Australia is great only 2 ways too even crank the car
1 have the actual key
2 swap out the BCM, ECU, Steering column with a different barrel and a key too match which takes ages
Anything else cuts power
informative. thanks
You re a master
excellent video thanks!!
How to disable the fuel supply on a muscle car with a mechanical fuel pump?
I can tell that man cares a lot about his watch
Gus Fring of all engines
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.
What if the intake manifold is off?
If you are compression testing, do you want and need oil in the engine? I would think so.
Muy bueno gracias
You have not mentioned the most important reading on the gauge...the reading of d 1st crank
coincidentally I'm using this video to check the compression on my own mercury cougar 😂
Brilliant cheers
piston has to be at tdc as well