Compression leak down test? how to?


#1

I have a 2000 Honda Civic. Every 1000 miles I am a quart low. I have noticed a loss of power too. I purchased a leak down tester and the direction on how to use it were vauge. This is what i did… Set my air compressor regulator to 80psi, then with the line closed I set the leak percentage gauge to 0 percent, then hooked it up to the cylinders when each was at TDC, was this correct? If so cylinder #1 had 30 percent loss, cylinder 2 - 29 percent loss, cylinder 3 - 36 percent loss and cylinder 4 - 22 percent loss. Are these percentages bad? the plugs looked simular the outer edge of the plug looked black and the insulator looked tan-ish white. Can anyone give me a clues or hints where my oil is going, where my power went, and if I am doing the test correctly? Thanks guys! (and gals)


#2

Forgot to mention the car has 128,000 miles


#3

You are doing good, now add some oil to the cylinders and see how much affect it has and do a normal compression test. One technique I have used on cars with high oil consumption and low power is to use a scope to look at the cylinder walls (checking for vertical scoring).

When you get it back together get a manifold vacuum reading. If you run your finger on the inside of the tailpipe is it oily? if yes this would give a indication to the severity of the oil loss.

You may be dealing with a normal wear and tear condition.


#4

Those losses are pretty high. Now what you need to do is, when doing a leak down on a cylinder, listen at the throttle body for air leaking, (intake valve), exhaust pipe for air leaking, (exhaust valve), and air leaking out of the valve cover oil cap hole, (rings).

Tester


#5

A quart every 1000 miles is not too bad…30% leak down is not too good…I think Honda’s use the aluma-sil engine block and no sleeves. Usually, this engine building technique works quite well, the steel piston rings riding on the silicone “liner” that forms in the cylinders. But sometimes the silicone fails and the rings dig into the aluminum cylinder walls… I think perhaps any problem in the air intake that allows dust to get in the engine can result in this problem. Squirt a little oil in each cylinder, turn the engine over a few times and repeat the test. If the numbers greatly improve, it’s rings/cylinder walls…


#6

The loss is high.
Perform a straight dry compression test and follow that up with a wet test. If the numbers are down but go up with a wet test then the rings are at fault. If the numbers stay down then it’s valves.

Oil loss is either rings or valve seals. (assuming no leaks)
Irregular oil changes or even one overheating episode in the past can ruin piston rings or cook valve seals.

If the compression is down then you should go and inspect valve lash followed by retesting the compression. Factory recommendations of allowing mechanical lifters to go a 100k miles and more without inspection is pure idiocy in my opinion.

If the lash is tight (usually it’s the exhaust valves and overheating can help this along) then odds are the valves and valve seats are already damaged. This means valve job time.
The reason I mention overheating in regards to the valves is that the exhaust valves especially have a tendency to suffer valve stem stretch over time. Throw overheating into the mix and they may stretch even more. This in turn means less. or no lash, followed by burned valves/valve seats. Hope some of that helps.


#7

A leakdown test is used to determine how well a cylinder is sealing at the valves and the piston rings. A cold (or, even, a warm) engine will seal poorer than a hot engine; but, it’s not possible to do a leakdown test on a hot engine. It’s still a useful test on a cold, or warm, engine.

You should find this information useful on using a vacuum test gauge: http://www.secondchancegarage.com/public/186.cfm Click on a green Scenario button for a gauge demo.

A vacuum test, also, is used to determine how all the cylinders are sealing, en mass. The test can be done, with a vacuum test gauge, on an engine hot or cold. While the engine is hot, is the time when the engine (and engine sealing) are at their operating best, and you will get the best vacuum readings.


#8

my wife and I bought the car new. It has never overheated on us. I will try the wet test tonight when my wife gets home. The lifters are hydraulic I believe, I don’t know if there is any adjustments.