Okay, here is a problem for those of you guys who are good at math (I am hopeless in that department lol). I ran a compression test today and the mechanic said the numbers for my cylinders were 15 - 14.5 - 14.7 - 14.5. I presume it's all in kilograms per square centimeters. How the heck am I supposed to know if my engine is in good shape or not? The engine is an F23A4. Thanks in advance!

UPDATE: I have been able to convert that to psis - 213 - 206 - 209 - 206 psi. How do I convert that to a compression ratio?

 

Why are you trying to convert that into a compression ratio? Compression tests do not compare the results to anything but itself really... You compare the 4 results of your test (1 result per cylinder) to make sure there is not a large variance in one or more of the cylinders. Your results show a healthy motor.

Two different people conducting the test can have two different sets of results on the same exact motor, due to the nature of the test procedures and even the equipment used. There wouldn't be much point trying to compare it to the compression ratio or even another F23 motor.

 

Exactly, the compression ratio is the ratio of the volume in the cylinder when the piston is at Bottom Dead Center to the volume in the cylinder when the piston is at TDC. It's determined by the geometry of the engine.

 

I see your point about the variance, but what about the normal compression ratio? I thought that by comparing my results to the norm I could deduce the extent of tear and wear of my piston rings. My engine has 195 k miles on it, and it looses about a quart of oil per 1000 miles, so I am getting worried that maybe I should begin to think about replacing my piston rings and/or valve seals...

 

Besides, some people are saying that 213 psi may be a little too much for this engine and may be a sign of excess build up on the combustion chamber walls. Does that sound right? If so, is there some liquid that I could pour in to fight the build up?

 

213 is within the acceptable variance of your other cylinders. I wouldn't worry about about any kind of piston ring wear, as your numbers would be much, much lower if they were excessively worn. I think the lowest acceptable numbers are around 160 or 165, and that's with a little room for variance due to equipment and test procedure.

If you're worried about carbon build up in the cylinders, you can run some seafoam (or any other good top-engine cleaner) through your motor. Do a search for "seafoam" if you're not aware of what that entails.

For the oil leak, I would be more concerned with checking the spark plug tube seals and valve seals, aside from the more obvious leaks such as the valve cover gasket, oil pan gasket, etc.

 

Thanks for your advice! Well, I have oil on the outside of the engine, so a couple of seals are definitely leaking, but I don't see any oil under the car in the morning, so there is no way it can loose a quart per 800 miles because of the engine seals...

So I am more worried about oil getting burned in the cylinders, which is indirectly corroborated by white build up on the spark plugs. My question is, with compression being so high, is is possible that oil gets in the combustion chamber through the piston rings? Or can I rule that out and focus on the valve seals?

 

I would focus on seals other than the piston rings. If compression was just excessively high (don't worry, it's no where close, and not likely to happen), and/or your piston rings were worn, you would probably have a lot of blow-by (exhaust entering the crankcase). Oil would not be pushed into the cylinders, as that would be acting against all the pressure.

Valve seals and spark plug tube seals are common areas to look at. Also track down your external leak, as some of them might be replaced while tracking down the internal leaks...

 

Philad, got you! Will replace the valve seals as soon as they are delivered and see if it helps. Thanks!