You want me to calibrate the gauge? Mechanics have said each gauge reads differently, but what is important is how close the cylinders are, although I am pretty sure being at or below minimum specifications is important. From what I can tell, I can find a place that will calibrate your gauge or hook it up to a compressor and compare gauges. I would need a compressor for a leakdown test.
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With the above said, you squirt the tablespoon of oil (SAE 30W is fine) into a cylinder that is reading low. Crank the engine two revolutions or so to spread the oil then retest the cylinder. If the compression comes up markedly, 40 PSI or more, the trouble is poor ring to bore sealing. If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head.
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Technical Articles at Greg's Engine & Machine
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Reading results
No engine will have perfect sealing with 0 percent loss. Five to 10 percent loss indicates an engine in great to good running order. An engine between 10 and 20 percent can still run OK, but it’ll be time to keep an eye (or ear) on things. Above 20 percent loss and it may be time for a teardown and rebuild. Thirty percent? Major problems. The percent of leakage should also be consistent across the cylinders. Any great differences indicate a problem in that cylinder.
Hearing problems
Beyond getting an overall picture of engine condition, the engine leakdown test is an excellent way to pinpoint where problems are before tearing down the engine. Listening for where the air is escaping by ear can isolate the problem.
Intake valve : Air whistling out of the intake, carburetor or throttle body indicates a leak at the intake valve.
Exhaust valve : Air heard hissing out of the tailpipe, turbocharger or exhaust manifold means an exhaust valve leak.
Piston rings : Whistling or hissing out of the PCV valve, oil filler cap hole or dipstick tube means the air is pushing past the rings. Suspect ring or cylinder wall wear.
Head gasket : Air bubbles in engine coolant seen at the radiator filler cap could mean air escaping into the coolant past the head gasket.
Cracked cylinder head : Bubbles in coolant or coolant being pushed up out of the radiator neck can also indicate cracks in the cylinder head or cylinder walls.
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https://mobiloil.com/en/article/car-...-leakdown-test
Now I want to see if Mobil has a compression test page, but it is kind of irrelevant!
Compression increased 12 - 18 PSI from wet to dry--"If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head." My car has lost 19.5 - 27% per cylinder. "it may be time for a teardown and rebuild."
Does it actually benefit me to know what the specific problem is? I love data, but I am not sure this is worth the time, energy, and money. Meanwhile, if I rebuild the engine, I will replace all of the seals and inspect the metal components.
Warped head--on my car? Wouldn't I have that machined like for the Subaru head gasket? Pulled head studs?
Weird. Most people obsessed over replacing the head studs when I replaced the head gasket, but RockAuto's kit does not include it: RockAuto offers a DNJ ENGINE COMPONENTS EK297M Master Kit; Includes Oil Pump & Timing Belt or Timing Kit for $369.99. Perhaps looking for another car would make more sense, but I probably would not be able to get another HX.
Rebuilding the engine would save me money eventually over driving the Accord daily. It is an automatic!