[gizmopt2002]

According to the FSM:

Compression pressure
Minimum pressure
Difference between each cylinder
1.3 MPa (13.3 kgf/cm2, 189 psi) or more
1.0 MPa (10.2 kgf/cm2, 145 psi)
0.1 MPa (1.0 kgf/cm2, 15 psi) or less

My results:
1 - 150
2 - 160
3 - 150
4 - 150
5 - 140
6 - 150

Synthetic its whole life, 160k

Is this normal? Kinda discerning one cyl. is below the minimum and the others are right there.

[BlackWorksInc]

How are you doing the compression test and how many "Puffs" of the gauge are you doing?"

[gizmopt2002]

I'll get back to you on that, it was done by a shop.

[fdbyrne]

How are you doing the test?

When I did mine on my old Tacoma I first did it with all of the plugs still in place except for the one that I removed to insert the compression tester. The engine has to work harder to crank when all of the cylinders are sealed off like that.

I think you're supposed to do it with all the plugs removed. That really helped my numbers.

[gizmopt2002]

They had at least one side out. They sent me a picture with 3 spark plugs. I'll find out in the morning when I pick it up.

[RonJR]

Keep in mind that there is nothing precision about the normal compression test on an engine. To a first approximation, the pressure should be equal to the (compression ratio -1) times the local atmospheric pressure. However, that gets modified by the adiabatic constant of the intake charge, which changes with air fuel mixture. It also gets modified by how fast the compressed air dumps heat to the cylinder walls, and by valve timing. All of this stuff has more or less effect depending on cranking speed. Finally, throttle opening determines to some degree how much air gets pulled in during the test and will also affect the numbers.

Bottom line, it's very difficult to compute the proper value. The number in the factory service specs is empirically determined by testing a known good engine under a specific set of conditions. If you don't do the test exactly as the FSM specifies, you'll get different results.

Also note that the target compression numbers drop by about 4-5% per thousand feet of elevation, since there's less air to compress at higher altitudes. Here in front range Colorado, at 5000 feet, 125-135 psi is typical of a good engine.

[Carwoman]

Originally Posted by RonJR

Keep in mind that there is nothing precision about the normal compression test on an engine. To a first approximation, the pressure should be equal to the (compression ratio -1) times the local atmospheric pressure. However, that gets modified by the adiabatic constant of the intake charge, which changes with air fuel mixture. It also gets modified by how fast the compressed air dumps heat to the cylinder walls, and by valve timing. All of this stuff has more or less effect depending on cranking speed. Finally, throttle opening determines to some degree how much air gets pulled in during the test and will also affect the numbers.

Bottom line, it's very difficult to compute the proper value. The number in the factory service specs is empirically determined by testing a known good engine under a specific set of conditions. If you don't do the test exactly as the FSM specifies, you'll get different results.

Also note that the target compression numbers drop by about 4-5% per thousand feet of elevation, since there's less air to compress at higher altitudes. Here in front range Colorado, at 5000 feet, 125-135 psi is typical of a good engine.

Thank you SO much for the reminder about altitude affecting pressure. I'm going to test mine this weekend and would have likely not thought about it and assumed the engine was screwed. (it probably is still screwed with a bad head gasket thanks to some inept mechanics who kept telling me I didn't have a problem, so I'm doing the work myself now!)

[pahaf91]

here in Sacramento where the altitude is about 150 above sea level, i got 180-185 PSI all across 6 cylinders. I did the test with all spark plugs out and cranking it about 5 times. I do have a blown head gasket in cylinder number 4. and it read 185psi as well.

[Captsolo]

Originally Posted by pahaf91

here in Sacramento where the altitude is about 150 above sea level, i got 180-185 PSI all across 6 cylinders. I did the test with all spark plugs out and cranking it about 5 times. I do have a blown head gasket in cylinder number 4. and it read 185psi as well.

What year 4runner? How many miles?

What caused your blown HG? do you know?

You might want to try Blue Devel before you tear down the heads at a shop. Some get three years of use.

Does your coolant level drop every time you drive?

[Oneluv13T4R]

Originally Posted by Captsolo

What year 4runner? How many miles?

What caused your blown HG? do you know?

You might want to try Blue Devel before you tear down the heads at a shop. Some get three years of use.

Does your coolant level drop every time you drive?

Why in the heck would you recommend pouring crap like Blue Devil in their engine as a temporary fix/band aid instead of fixing the issue properly when the issue arises. thats the most stupidest thing I've heard and should never recommend that kind of advice.
fixing a head gasket isnt a complicated job, but with a mentality like that I can only assume many things must get band aids that cross your path. never recommend crap fixes unless the person is asking for that advice. just my .02!