I'm looking at a 3.0CS with compression numbers across all 6 cylinders at about 100 psi (and minimal variation among them; less than 5%). The low variation is obviously good, but the 100psi is in my opinion either unacceptable, or just barely acceptable, indicating a fairly tired engine. I would benefit from hearing others' opinions, though. Thanks in advance.
compression #s
- Thread starter ajf
- Start date
Honolulu
Well-Known Member
That's low, but the even-ness makes me wonder if the test was done correctly. All throttles held open, plugs removed, four to five compression strokes, maybe a little light oil in the cylinders if not run lately...
Get a backup compression tester.
There's little chance those numbers are correct
There's little chance those numbers are correct
Why? Because (a) they are unlikely to be so consistent? (b) they are unlikely to be so consistent at this low of a compression value? or (c) because they are unlikely to be this low overall? I'm guessing you mean option (b).
Unfortunately I didn't do the compression check myself so can't vouch for how it was done.
Thanks for the input.
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Yes gauges can vary, also ambient temp, temp of engine (it was done warm, yes?), throttles wide open, plugs off as menitoned. How does the car run?
B is the answer
Anything that worn is unlikely to be worn so evenly
Try another mechanic with a different tool.
Anything that worn is unlikely to be worn so evenly
Try another mechanic with a different tool.
I will get another compression test or, better yet, do it myself. It seems to run ok whatever its compression numbers are.
Are others in agreement that 100 across the board, more or less, is on the bottom end of barely acceptable? I really don't feel like being the one holding the car when the engine requires major attention...
Thanks again, all.
Are others in agreement that 100 across the board, more or less, is on the bottom end of barely acceptable? I really don't feel like being the one holding the car when the engine requires major attention...
Thanks again, all.
I have never seen a car test like that.
Don't believe it.
Don't believe it.
The statistical chance that six cylinders would all be down 38% from normal and all be within 2% variance of that norm is
Unlikely!
Unlikely!
Dude, I was not questioning anything anyone said about the irregularity in readings, and in fact I deeply appreciate the input and expertise.
The only issue at the time when I asked for additional input from others was regarding how low people interpret 100 to be, since that was not really addressed (the only input about that was "that's low" at that point). I agree it's low, I was only hoping to hear opinions on whether it's "run away from it" low or "drive it and don't fret" low. Sorry if I offended anyone by asking questions, but I thought that was in the spirit of the board. I'm here to learn from others and if possible help others too.
Thanks again to all who have taken the time to provide input, I'm genuinely grateful.
Honolulu
Well-Known Member
Look on the bright side (always)... and never compression test an engine that isn't running poorly enough that you'd consider seeing your banker to determine why.
Compression testing just came up with a pal who got a small ancient outboard motor for which all parts are NLA. He borrowed my compression gage, then complained the engine wouldn't turn over. Of course, the piston was hitting the adaptor screwed into the sparkplug hole. So I brought my hold-it-in-with-your-thumb tester that I got 40 years ago in my aircooled VW days, and we (this time)did it again: low compression on one of two cylinders, didn't even try the other. Also noted a helicoil in one plug hole, so there's no end to how bad it could be/get. He only wants it as a kicker for a small sailboat (he's far too outa shape to row). I told him heck, as long as it runs, it'll hold against the tradewinds, and Bob's yer uncle.
Whatever... if you can live with how the car runs now, it may not get much worse, and what you're looking at, is how it'll be.
This all assumes the original set of numbers weren't someone's imagination or fabrication.
Compression testing just came up with a pal who got a small ancient outboard motor for which all parts are NLA. He borrowed my compression gage, then complained the engine wouldn't turn over. Of course, the piston was hitting the adaptor screwed into the sparkplug hole. So I brought my hold-it-in-with-your-thumb tester that I got 40 years ago in my aircooled VW days, and we (this time)did it again: low compression on one of two cylinders, didn't even try the other. Also noted a helicoil in one plug hole, so there's no end to how bad it could be/get. He only wants it as a kicker for a small sailboat (he's far too outa shape to row). I told him heck, as long as it runs, it'll hold against the tradewinds, and Bob's yer uncle.
Whatever... if you can live with how the car runs now, it may not get much worse, and what you're looking at, is how it'll be.
This all assumes the original set of numbers weren't someone's imagination or fabrication.
I reread this thread, and I read Don's posts to strongly suggest that you not make a decision based on the data you have in front of you. This is the reason why we are not responding to the question "what would you do if your compression readings were in the range of 100 psi?" We might be leading you down the wrong path.
TREMK
Well-Known Member
ajf, If you have found a good solid rust free car just figure the cost of engine overhaul or 3.5 upgrade into your price negotiations if the engine truly is tired. One of the most costly jobs with these cars is major body work. Would like to see compression in the mid 100's or better. If you give your location maybe someone local can advise. Welcome and good luck. Mike