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 Post subject: Can somebody walk me through a cylinder leakdown test?
PostPosted: Tue May 15, 2018 1:35 am 
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I am merely driving my van
I am merely driving my van

Joined: Sat Apr 21, 2018 1:02 am
Posts: 2
So, i just got done doing a kindof preview cylinder leakdown test(it got dark so i just tested the main suspect cylinder, #4 because I found oil on the inside of the plug accompanied by smoke out the tailpipe), but im not %100 sure i did it correctly because ive never seen one done and only had the internet as my coach...

Here's what i did:
Engine cold(all the plugs were already out and i just wanted to try out the tester)
All plugs out
TDC on #4
Compressor at 100psi
Tester at 15psi

Here's what i saw/heard:
%10 immediate leakdown
More like %20 after a small amount of time(plus the compressor kicked back on so i dont know how accurate the reading was)
I heard air leaking through the oil filler tube(no noise at exhaust and no bubbles in coolant)
Attachment:
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(Blah blah harbor freight tools, didnt wanna spend $150+ for something im hopefully not going to have to use a lot)

If time permits, i aim to do a complete test tomorrow. So if someone could spell out for me exactly how to do this test and/or tell me what im doing wrong or what im not doing at all, thatd be great!

Also, i'm new here. Thanks for having me!


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 Post subject: Re: Can somebody walk me through a cylinder leakdown test?
PostPosted: Tue May 15, 2018 5:59 am 
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I sleep in my van

Joined: Sun Jan 13, 2008 5:23 am
Posts: 738
Hi,

Did you do compression test? Dry and wet?

Or does the leak down tester eliminate the need to do compression test?

How many miles on engine?

Welcome and good luck.

AP


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 Post subject: Re: Can somebody walk me through a cylinder leakdown test?
PostPosted: Tue May 15, 2018 4:40 pm 
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ASV Supporter
ASV Supporter

Joined: Tue Jan 02, 2018 2:11 am
Posts: 98
Welcome, and congratulations on having the ambition and going a step farther with the tool purchase.
I used to use a leakdown test quite a bit when I was wrenching for a living. It expensive at the time ( 30+ years ago) but still an inexpensive model, compared to the professional versions.
I always used the information derived from that test along with the compression test.
A compression test gives you a meaningful, but general, idea of the combustion chamber sealing. ( By doing both dry and wet tests, a relative indication of ring sealing can be obtained)
The leakdown test will add some information about the source of leakage, even if low compression is not an issue.
Using a leakdown tester on just one cylinder does not help very much. It will give you an idea of the source of leakage but it really needs to be compared to the other cylinders if you are attempting to find the reason for a specific problem.
I think the readings may vary quite a lot, from one inexpensive test device to another. Maybe aircraft quality units are calibrated with some specific orifice size, but I doubt the inexpensive ones are so accurate between devices.
Having said that, I don't think it is particularly important for our use.
The idea is to get a reading of 'relative' leakage on each cylinder, under similar conditions; and to determine as best you can, the source of the leakage ( listening at carb/FI opening, crankcase vent and exhaust).
Compare those findings with the different cylinders and you 'may' find a correlation with the compression readings and/or symptoms (such as your oil issue). Keep in mind that oil consumption through worn valve guides may not show up on either test.
The leakdown test is just another tool, to help pinpoint problems.
Rod J
Issaquah, WA

_________________
WE7X aka Rod Johnson
Forest Green Metallic '98 LS AWD
Issaquah, WA


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 Post subject: Re: Can somebody walk me through a cylinder leakdown test?
PostPosted: Tue May 15, 2018 5:53 pm 
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I am merely driving my van
I am merely driving my van

Joined: Sat Apr 21, 2018 1:02 am
Posts: 2
Astrophysics, my dry compression test came out to 155psi across the board, with maybe 2psi difference on one or two cylinders. I have not done a wet test. Engine has 100,040 miles on it. Oil is clean, coolant is clean, the machine drives fine just has a horrible idle accompanied with some ugly smoke out the tail pipe.

WE7X, thanks for the comments. I knew doing just one cylinder wouldnt tell me much but it had gotten a bit late to be running my compressor outside, but i just wasnt even sure if I was performing the test properly in the first place... Im gunna get back out there after work and get some readings for all six.

Have a good day my dudes!


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