Comparison Between Compression Testing- & Leakdown Testing Results on a '99 Corolla VE

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I present comparative engine health testing results on my '99 Corolla... with about 127,000 miles on it. Car was acquired with about 100,000 miles, some 15 or so years ago. Not much use 🙂.

I tested the car cold, using the FAA directed leakdown testing method (used for piston engined aircraft). My reason for the FAA process is because in the automotive world no standard exists for the orifice used for the leakdown testing equipment. FAA is, by comparison, very specific. Limits of rejection for the FAA test is 25% leakdown.

I also tested the car hot, using the same test rig. Finally, I tested with my compression tester, hot, with throttle on the floor and fuel inj. relay pulled.

See comparative results, attached.

My Dad's '50's or 60's vintage SnapOn compression tester says, on the face of the gauge, that cylinders should be no more than 10 psi different from one another. Others say cylinders should be no more than 10% different from one another (using the classic compression test). Incidentally, I did not use my old SnapOn; it's too old and likely has lost accuracy, leaks, etc. I have a much newer device.

My point in showing the comparison between traditional compression testing and leakdown testing is that they tell different stories, sometimes. With a traditional compression test, not only the final figure is important, but the vigour with which it reaches the final figure. If you get high compression pressures, even on the 2nd "hit", that's vigorous and healthy. If it agonizingly slowly gets to final... that's not so good.

Incidentally, all quick-connect fittings downstream of the restriction orifice, on my (rather ugly) leakdown tester are pressure washer type... low restriction/through-bore. If they were traditional compressed air type couplers they might affect the results.

Discussion on this would be welcomed!
 

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One follow-up comment: it's quite easy with leakdown testing to rotate the engine backwards by mistake. This can have really dire consequences... i.e. binding-up the camchain or timing belt slack-side tensioner, and causing the engine to skip a tooth or more. It is critical that you start from BDC on compression and stop the barest amount before TDC... like 1/2 of a degree to prevent this. On the other hand, to obtain accurate results you will want to ensure the rings load the bottom piston ring lands on the piston... so always go in one continuous pull from BDC to that 1/2 of a degree before TDC and you should have no prbs.

NP at all with cyls 1 and 3 on my 1, 3, 4, 2 firing four cylinder... but if BDC is NOT pre-marked by the mfr (often it is not) you need to be very accurate in putting a paint dot to mark it yourself! Use a caliper to determine the pulley dia. (on its belt flange/rim) and calc the half-circumference... and use a tailor's measuring tape to find BDC in that manner.
 
Q: What do you mean by a standard orifice isn't used for leakdown testing of automotive ICE?

For automotive applications I've only seen wet and dry tests where a pressure gauge is attached by way of the spark plug hole and the engine is dry started to build up pressure. Standardization isn't required.
 
Looks like you have more invested in the test equipment than the car. Looks fine to me but you're using too much pressure in the leak down test. 35 psi is enough. Even with some orifice, 80 psi is too much. This ain't a Cessna.
 
Looks like you have more invested in the test equipment than the car. Looks fine to me but you're using too much pressure in the leak down test. 35 psi is enough. Even with some orifice, 80 psi is too much. This ain't a Cessna.
Ah, most automotive leakdown testers use 100 psi, not 80. 35 psi? Nah, no one uses less than 80... As to $ invested, it cost me next to zero. Remember; I said its ugly...

Have you guys never heard of leakdown testing? Precision engine builders use 'em all the time as a test of the quality of their builds... A quality build gives 2, 3, or 4% leakdown. Less than 5% in any case.

 
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Q: What do you mean by a standard orifice isn't used for leakdown testing of automotive ICE?

For automotive applications I've only seen wet and dry tests where a pressure gauge is attached by way of the spark plug hole and the engine is dry started to build up pressure. Standardization isn't required.
You're talking about a standard compression test (which I did perform, hot and dry). I did a leakdown test, using an FAA std 0.040" dia. X 0.250" long orifice.
 
Looks like you have more invested in the test equipment than the car. Looks fine to me but you're using too much pressure in the leak down test. 35 psi is enough. Even with some orifice, 80 psi is too much. This ain't a Cessna.

35 psi won't tell you anything. You need enough pressure to load the rings. Running at
I do regular leakdown testing, but I use a simple Longacre setup that I bought from Summit.
 
I present comparative engine health testing results on my '99 Corolla... with about 127,000 miles on it. Car was acquired with about 100,000 miles, some 15 or so years ago. Not much use 🙂.

I tested the car cold, using the FAA directed leakdown testing method (used for piston engined aircraft). My reason for the FAA process is because in the automotive world no standard exists for the orifice used for the leakdown testing equipment. FAA is, by comparison, very specific. Limits of rejection for the FAA test is 25% leakdown.

I also tested the car hot, using the same test rig. Finally, I tested with my compression tester, hot, with throttle on the floor and fuel inj. relay pulled.

See comparative results, attached.

My Dad's '50's or 60's vintage SnapOn compression tester says, on the face of the gauge, that cylinders should be no more than 10 psi different from one another. Others say cylinders should be no more than 10% different from one another (using the classic compression test). Incidentally, I did not use my old SnapOn; it's too old and likely has lost accuracy, leaks, etc. I have a much newer device.

My point in showing the comparison between traditional compression testing and leakdown testing is that they tell different stories, sometimes. With a traditional compression test, not only the final figure is important, but the vigour with which it reaches the final figure. If you get high compression pressures, even on the 2nd "hit", that's vigorous and healthy. If it agonizingly slowly gets to final... that's not so good.

Incidentally, all quick-connect fittings downstream of the restriction orifice, on my (rather ugly) leakdown tester are pressure washer type... low restriction/through-bore. If they were traditional compressed air type couplers they might affect the results.

Discussion on this would be welcomed!
In the interest of completeness, do a running compression test and compare. Running test shows how well the engine is breathing, among other things.
 
Thanks for sharing.

In the shade tree auto world its not really used for this.

You do a compression test to determine overall engine health. If there all fairly close - good enough.

If you have operation problems you do a compression test to see if that is it. You do a wet and dry leakdown to determine if its the rings or valves.

Absolute pressure in a car engine doesn't tell you a lot generically, at least for daily driver use.
 
I use leakdown tests for all my small engines. Most of them have compression release which makes doing any meaningful compression test difficult. The hardest part of leak down testing larger engines is always getting the cylinder your testing to compression stroke top by yourself and keeping it there.
 
Clap your hands. That pop sound is compression... but with 100% leakdown. I've seen quite a few engines that were burning oil, compression test was consistent 180-190 psi but 2 cylinders showed >20% leakdown and 3 more at 15-20%. Compression test is a poor check of engine health.
 
Clap your hands. That pop sound is compression... but with 100% leakdown. I've seen quite a few engines that were burning oil, compression test was consistent 180-190 psi but 2 cylinders showed >20% leakdown and 3 more at 15-20%. Compression test is a poor check of engine health.
That's been my experience. Look at my numbers. Hot compr test looks 'real good. Hot leakdown, not so much. Leakdown test is more severe and allows you to much more so pinpoint source of the prb. If you buy a commercial leakdown tester just be sure the one you're buying actually HAS an orifice! Some of the more inspired designs (heavy sarcasm) DON'T!
 
Thanks for sharing.

In the shade tree auto world its not really used for this.

You do a compression test to determine overall engine health. If there all fairly close - good enough.

If you have operation problems you do a compression test to see if that is it. You do a wet and dry leakdown to determine if its the rings or valves.

Absolute pressure in a car engine doesn't tell you a lot generically, at least for daily driver use.
Yeah, I'm not dealing with a race engine, for sure. I was trying to diagnose a prb... and I had the plugs out (for replacement) and I've had that leakdown tester for donkey's years. Easy enough to do on a four cylinder, in any case. Quite easy to accurately find and mark TDC for cylinders 2 and 3. Being WRONG with that marking can have dire consequences in some engines though... so I'm very careful.
 
In the interest of completeness, do a running compression test and compare. Running test shows how well the engine is breathing, among other things.
@willbur, I don't know a whole lot about running compression tests. Can you further explain? What does it tell you? Is it hard on the tester? Do you need to introduce some kind of orifice in the line to lessen potential compression test gauge damage?

I can imagine that on a four cylinder you leave the sparkplugs and ignition intact on all but the cylinder you're testing. It'll start and run, but poorly...

??
 
@willbur, I don't know a whole lot about running compression tests. Can you further explain? What does it tell you? Is it hard on the tester? Do you need to introduce some kind of orifice in the line to lessen potential compression test gauge damage?

I can imagine that on a four cylinder you leave the sparkplugs and ignition intact on all but the cylinder you're testing. It'll start and run, but poorly...

??
There's alot of internet info available. Google "running engine compression testing"
 
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