Cylinder compression numbers

[bighorse]

My 03 200 BR (5.0 MPI - Alpha G2) was leaking drive lube and the dealer determined the leak was at the impeller housing, which was limiting the amount of water being pumped to the engine. They said, based on this, it should have been running hot. It always indicated 175 or so on the water temperature gauge, which I was told was normal. Now I'm wondering if there was enough water being circulated to even register the temperature.

The exhaust flappers were melted, so it got at least hot enough to do that, but I never got an alarm of any sort, and the engine ran fine. I just had to keep filling the drive lube reservoir. I ran it enough that, if the engine was being damaged, I think there would have been symptoms. Oil pressure was always good, I never heard anything out of the ordinary, and the exhaust manifolds were only slightly hotter than touchable.

I asked them to run a compression test to determine if the engine got hot enough cause damage and the manager told me they got 115-120 psi on all 8 cylinders. I've ran compression tests before on Chevy v8's and always got in the 140-150 range. The engine has 43 hours on it, so it should still be fairly fresh. Do those numbers look right?

 

[fc3]

Bit on the low side for a new engine, even if it was cold. But the numbers are within spec.

 

[berth control]

that is all I have ever gotten in compression tests. I think some people leave all the plugs out and then the motor spins faster, higher compression. I wouldn't worry at all.

 

[fc3]

Generally the methodology is to remove all plugs, open the throttle, install the gauge, and turn the engine a few turns until the peak reading is reached.

Best regards,
Frank

 

[northern]

If you take all the plugs out do a compression test then squert oil in the cylinders and redo the compression and it goes up 30 PSI or more you probably got problems with your rings or sleeves. The rings could be cabron locked up or your cylinder sleeves are worn or your rings are too hard. If your plugs had a lot of carbon on them you may have carbon locking up the rings or your valves are not fully setting.

 

[stevea661]

You should warm your engine to operating temp before you test. This gives every thing an chance ti heat up and expand. Remove all your plugs and then test. If adding oil to a low cylinder causes it increase alot, it's rings. If it doesn't its probably valves. You can figure out more with a leakdown test but thats a little more involved.

 

[ShamuToo]

You should warm your engine to operating temp before you test. This gives every thing an chance ti heat up and expand. Remove all your plugs and then test. If adding oil to a low cylinder causes it increase alot, it's rings. If it doesn't its probably valves. You can figure out more with a leakdown test but thats a little more involved.

I second that. Pistons are aluminum and expand at a different rate. Cold motors allow a bit more pressure to slip by the rings. The discussion about all the plugs being out and spinning the motor a few times to peak the reading is also correct. Try all that and look for 150 psi.

 

[gerryb]

If 120 +/- is consistent across the cylinders, and you tested the engine cold, you are fine.