Compression reading?
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Junior User
Joined: Sep 2009
Posts: 71
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From: Rochester, MN
Compression reading?
Hello all,
Well Friday I got a chance to have my truck tested for its compression
and I think the results are pretty good (to me at least...I was expecting
the worse :-). Anyway, all cylinders tested at 150 except for the number
2 cylinder which was 138 or so. How does this sound to you guys?
Jim
ps
My friend kept smelling a coolant smell so he thought I may have a blown
headgasket. However, since then I believe my radiator is leaking ;-(
Jim
Well Friday I got a chance to have my truck tested for its compression
and I think the results are pretty good (to me at least...I was expecting
the worse :-). Anyway, all cylinders tested at 150 except for the number
2 cylinder which was 138 or so. How does this sound to you guys?
Jim
ps
My friend kept smelling a coolant smell so he thought I may have a blown
headgasket. However, since then I believe my radiator is leaking ;-(
Jim
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Joined: Dec 2007
Posts: 7,986
Likes: 104
From: Boise, Idaho
150 is very good compression, I'd feel good about that.
The 138 is an 8% variation from the rest though. It's the % that makes a difference.
An 8% isn't bad (I can't remember above what variation you need to start worrying, but I'm pretty sure you're not there.)
Maybe take it for a drive and test again. Also, if you have a blown HG, check for coolant in the oil, or visa versa. You can also have a shop to a pressure test to see if your headgasket is okay. If it is, there are a few other tests you can do to see why the compression in #2 is slightly lower, like putting a little oil down the spark plug hole and trying again. IIRC, if the compression goes up, the rings are worn. If not, your valves are little worn.
Either way, your compression looks like it's pretty good.
The 138 is an 8% variation from the rest though. It's the % that makes a difference.
An 8% isn't bad (I can't remember above what variation you need to start worrying, but I'm pretty sure you're not there.)
Maybe take it for a drive and test again. Also, if you have a blown HG, check for coolant in the oil, or visa versa. You can also have a shop to a pressure test to see if your headgasket is okay. If it is, there are a few other tests you can do to see why the compression in #2 is slightly lower, like putting a little oil down the spark plug hole and trying again. IIRC, if the compression goes up, the rings are worn. If not, your valves are little worn.
Either way, your compression looks like it's pretty good.
