Compression test failed?

[paulw]

Compression on the 200CI 6 cylinder 68 Mustang is

135
145
185
140
150
155

Heads look like they have just been rebuilt with fresh paint. The block has what may be 40 years of grease caked on it. What do you think is going on with #3 at 185lbs? I was about to upgrade to DurasparkII, but not sure I want to spend the $$ now.

paulw
Torrance, CA

 

[rocklord]

Did you run the compression test dry?
If so, squirt some oil into the cylinders, then retest.

 

[rbohm]

Compression on the 200CI 6 cylinder 68 Mustang is

135
145
185
140
150
155

Heads look like they have just been rebuilt with fresh paint. The block has what may be 40 years of grease caked on it. What do you think is going on with #3 at 185lbs? I was about to upgrade to DurasparkII, but not sure I want to spend the $$ now.

paulw
Torrance, CA

8) except for cylinder number three, the number look pretty good. rerun the test dry and the wet and see what happens.

 

[paulw]

OK, did a wet test:

Dry Wet
135 210
145 200
185 225
140 200
150 210
155 220

Unfortunately, I don't think I did the wet test correctly. I poured several unmeasured ounces of oil in each cylinder. Then after testing, checked instructions on the internet which said to only use a teaspoon of oil. I'll let it drain out of the cylinders tonight and try again tomorrow. My guess is that it will drain better from 1 2 4 5 6, then from 3.

 

[JackFish]

And do the test on a warm engine.

 

[rbohm]

8) your wet numbers look just fine. i think that 185 reading is a bit suspect though. i would say overall though the engine is in pretty good shape.

 

[fordconvert]

If the engine runs I usually do a compression test with it warmed up. How warm depends on how easy it is to get to the plugs. On our 6's its usually easy since the plugs are on the other side from the exhaust. I usually only resort to the wet test on an engine that has not run for a while.

What you are really looking for is that they are fairly close to each other.

 

[mugsy]

When I bought my car I had similar numbers as you. In my case the high number was on the cylinder that would oil foul in about 100 miles. I figured that the leaking oil was help sealing the rings and had more than likely gunked the rings up. Does that cylinder act the same as the others on your engine?

With the jump between dry and wet I'd say that the rings are bad. But I'm no expert; maybe others here will confirm or deny my diagnosis.

I'd think the "large" amount of oil you put in the cylinders will only mean that you'll get a nice white-blue cloud coming out of the tailpipe for while after restart.

 

[LaGrasta]

install the DS as planned (nice hot sparks are good) and put some miles on the car! This will clean and loosen the rings, etc. I'd pour some Marvel Mystery Oil in there as well and after a few thousand miles, change the oil and do another compression test, you may be surprised to see everything much more stable. Heat cycles and MMO does a lot for getting things where they need to be.

 

[mugsy]

GM used to have "combustion chamber conditioner". You poured a bunch down the throat of the carb while it ran and then the rest to make it stall out. Leave it sit for a while and then restart. Seemed to help mine a little. Hey, whatever you use can't hurt. Some of those products ask that you change the oil after they are used.

 

[ludwig]

Hey, whatever you use can't hurt. Some of those products ask that you change the oil after they are used.

Oh, I dunno. I got some 'oil solvent' to 'clean the oil passages' after the car had sat for a long time until I bought it. I poured it in and ran a couple miles like it said on the instrux. Two miles away from my house the oil light went on, there was a whirring and then it started to knock like a hammer on one side of the block.

So the oil pump shaft had fallen out of the bottom of the diz, There is a friction clip that holds it in place and that was gone. The top end lost all oil and, since it was thinned to the weight of turpentine and drained down to the pan, there was no residual lube to get me home at low speed.

So be careful what you put in there. That event hastened my decision to get a new long block.

 

[mugsy]

Well that's the first time I've heard that!! WOW. I was referring to the products you pour down the intake, like seafoam and combustion chamber conditioner and stuff like that.