Compression test results, how bad?

eburrows

Well-known member
On my D2 with 320k miles (~200k on this engine), I once heard bubbling in the heater core, and had a coolant over-pressure/temp dump, so I did a compression test:

1: 170
2: 180
3: 175
4: 195
5: 105 (140 with a squirt of oil)
6: 205
7: 170
8: 210

So, to the greybeards out there: Is this a "Holy crap, rebuild/replace that engine ASAP", a "Meh, drive it until you get misfires, etc." or somewhere in between?

It had a new head gasket (w/ machining) about 10k miles ago.

Thanks!
 

robertf

Well-known member
Jan 22, 2006
4,781
356
-
I'd ride it out since its news you probably don't want to hear. Had a 96 with similar problem. Block had cracked along with the liner, not rebuildable. It passed emissions and was a perfectly fine around town vehicle, though AC was practically worthless on that truck since the needle would climb almost instantly when on. Eventually it left me stranded and since it was my least favorite of the fleet it became donor parts for my other two.
 

eburrows

Well-known member
Jeff Blake: I changed the oil within the last month, and saw no milkyness.

jymmiejamz: I once heard bubbling on startup, but just once. I'm not aware of any event where the engine got overheated, but at least once I saw the expansion tank overflow spout flowing. At the time, I assumed it was due to engine shutdown heat spike, as I had just ascended a mountain trail, but it could also have been exhaust gases overpresurizing the system. I don't know which for sure.
 

squirt

Well-known member
Nov 13, 2008
824
13
Los Angeles
Those compression numbers seem a bit wonky in general. Not only do you have a wide range, but the numbers over 200 seem unusually high. (granted gauges can vary and the comparison between cyls is more critical)
 

eburrows

Well-known member
squirt: What's a normal value? Are the 170's normal-ish? I used a new MightyVac gauge, and checked all the cylinders once, except for #5, which I did a few times to make sure there were no sealing problems, etc.

One other thing, I did take a pic of all the spark plugs. None look excessively dirty (or steam cleaned) to me:
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eburrows

Well-known member
Thanks all, what I didn't hear was, "Holy, crap that thing's going to blow up any minute!", so, as with so many other minor issues, I'll put it on the list of things to keep my eye on, rather than actively worry about. Worst case, I have 300-mile AAA.