3.5 compression numbers

[mudpie]

Howdy.

I picked up a '98 Montero, not running, with some stuff off the motor because someone was digging for a coolant leak. It's a long story.

I want to do a compression test to see if it's a head gasket, but also to get a general idea of how solid (or not) this motor is. It's got over 300k, but was maintained pretty well. I don't know what compression numbers I should be expecting. I tried searching, but I keep coming up with info on compression ratio, not compression gauge readings. I'm sure the info is out there, but I'm time limited on the computer at the moment, which is also a long story.

Any input appreciated.

 

[nwoods]

Howdy.

I picked up a '98 Montero, not running, with some stuff off the motor because someone was digging for a coolant leak. It's a long story.

I want to do a compression test to see if it's a head gasket, but also to get a general idea of how solid (or not) this motor is. It's got over 300k, but was maintained pretty well. I don't know what compression numbers I should be expecting. I tried searching, but I keep coming up with info on compression ratio, not compression gauge readings. I'm sure the info is out there, but I'm time limited on the computer at the moment, which is also a long story.

Any input appreciated.

171 PSI standard, min of 127 PSI, maximum of 14 PSI difference between cylinders
page 11-A3 of the factory service manual from MitsubishiLinks.com

 

[evomaki]

What nwoods said. I recently did a test on a Montero I recently purchased and got a low on one cylinder of 170 with the highest cylinder at 180. This is on a cold engine with all plugs out and fuel pump disconnected, but warm outside. My intake was off, but I would at least hold down the throttle to open the throttle plate. I would have pulled a fuse to the fuel pump but I could not figure out where it was so carpet up inspection plate off and just old-school unplugged the fuel pump at the tank. This is for a vehicle with 160 thousand miles and probably average care by the previous owners. All gauges will be a bit different, and so it's not just the absolute but the relative cylinder to cylinder.

 

[mudpie]

...factory service manual from MitsubishiLinks.com

Nice link. Thanks.

I did the compression test. It's not a head gasket, but my numbers are a little odd. On the right bank, I got 90, 110, 90, dry readings. Squirted some oil in the hole and did it again and got 170, 210, and 230. Left bank I got 210, 120, and 210. I put some oil in the 110 hole and got 190. I didn't do the others two a second time since it was starting to rain. I'm going to put it back together and see what happens. I'm hoping the odd numbers were a result of the fact that it has been sitting for at least 6 months, and I was rushing to get done.

The guy I got it from said his daughter was driving it and reported that "it just stopped". When they checked it out, they found it low on coolant, so they had somebody start working on it but decided to sell it instead. Beyond that, he didn't know or couldn't remember much of the specifics. When I pulled the plugs, they were a disaster. The top row is the right bank (easy to get to), and the bottom row is the left bank. Not so easy to get to, and probably weren't changed in a while. I'm surprised it ran at all.

I'll throw plugs in it and put it back together. If it runs, I'll do the t-belt, water pump, and a bunch of other stuff, then the fun will begin.

Thanks for the help.

 

[Pntyrmvr]

Needs rings.


"Talk is cheap. Whiskey costs money."

 

[RyanY]

Judging by the looks of those plugs, I'd say the previous owner didn't really bother to maintain the vehicle. Probably just topped up the oil anytime it got more than a quart low rather than changing it regularly, and there's engine wear problems as a result.