2000 Montero Sport XLS, 212k on the clock. Doing some work on it and needed to pull the intake manifold. Since the engineers thought it would be a dirty trick to bury the spark plugs under the intake manifold, I'm doing those while it's all open. While they were out, I performed a compression test. Here's what I got:

#1 - 150#
#2 - 142#
#3 - 125#
#4 - 125#
#5 - 150#
#6 - 180#

 

theyre the rear cylinders? So they normally run hotter...
I would say thats actually enough deviation front to back to look at skimming the head.

 

I was speaking in terms of firing order:

5 6
3 4
1 2

| Specifications | Firing Order | AutoZone.com

 

so they're not the two rear cylinders?

do the "oil down he hole" tes which'll tell you if it's rings or not...

 

Correct -- the low cylinders are both center cylinders. I will do the oil test to confirm, but from what I've read elsewhere, the bottom ends on these motors seem to be pretty stout and problem free and most low compression issues tend to be with valves. I'm considering sending the heads out to be freshened up, but I'll definitely squirt some oil in there first to be sure.

What are the target compression numbers for a well sealed motor? What is typical of an older motor?

 

compression more about balance than numbers, yours id aim for 150.
If the oil test doesnt change it, you can do a leak down test to check the valves.