Compression Testing; Water Torture Test
 

I have a 1989 4 cylinder LE with 144k miles that I've owned for about two months. The engine seems fine and, while it won't win any beauty contests, passed California's smog testing upon purchase. I just regapped the spark plugs (which looked okay as to color/lack of soot), changed the spark plug wires/distributor cap, and ignition rotor. Upon purchase, #3 cylinder had a spark plug boot tip that broke and disintegrated, and I was just able to remove the debris to remove and check spark plug #3 (gap was 0.050" and regapped to specifications) and finish the above tune up.

There is no coolant loss, smoke from the tail pipe, and the oil and coolant look fine. It has never overheated on my watch.

Yesterday, I checked engine compression, engine warm, as a baseline, to get to know my car, and to rule out any engine problems that I might have missed. Readings were:

cylinder psi
1 148
2 153
3 151
4 156
average: 152

Haynes' says that 128 psi is minimum and 171 psi is normal. Thoughts on my readings? For a 25 year-old car with 144k miles, is my 152 average normal, or a sign of problems to come?

I've read that Seafoam, water, or a lipophilic solvent like isopropyl alcohol, introduced through an intake manifold hose, can clean up dirty combustion chambers, which, given the poor baseline condition/maintenance of my car, I presume is present. Thoughts on doing that? I presume that removing that gunk will increase the combustion chamber area, thus lowering my compression.

How often would it be prudent to check compression?

Thanks!

Suggest you may be overly concerned.

The 171 psi may be stated to be normal. But your compression ratios are well above the low of 128 psi and pressures are consistent between cylinders.

Water and alcohol can remove carbon but suggest not using either!! Some owners have removed the vacuum hose from the brake booster and added Seafoam here. The internet has post and video's on doing this.

My opinion is given the engine runs fine to do nothing.

Compression testing is typically done if low compression is suspected. Such as lack of power, blown head gasket, engine will not start.

If all is normal in the engine there is not much one can do to change compression ratios and most likely it doesn't mater. The real test is if the engine runs OK, doesn't use excessive amounts of oil, passes an emissions test, starts OK, has OK power, etc.

thanks!