Compression test interpretation help

[Kevin Breaux]

Old 5.9 magnum 225k miles . Dry/wet test help with interpretation please I know it’s worn out but trying to troubleshoot a smoking in the morning issue . Recently posted on another thread results but must not have done it right. This time controlled as possible. Engine completely warm .6 seconds per cylinder . Also using a oil can 3 squirts per cylinder . Of course throttle wide open and ign/fuel disconnected.

 

[dodge862]

Circled is the dry test I assume?
"Smoking in the morning" as in first start for the day it smokes some?

 

[jawzs2]

I'd pop off a valve cover and take a look at the valve seals, compression test doesn't look that bad.

 

[dodge862]

Valve stem seals was going to be my suggestion as well. Had a similar issue with stalling on startup and smoke from the exhaust.
But I'm also facing compression issues and trying to determine whether it's a problem with rings, valves, or something else... Wasn't ready to point in the wrong direction if I could help it

 

[crazykid1994]

I would say for one that compression is a bit low. If I remember correctly my 318 tested 120 dry and 130 wet but had 2 cylinders dry tested 90s and wet tested 120. That was rings going bad. Almost seems like you may be having a valve sealing issue possibly just from carbon buildup but that’s not your early morning smoking. That’s from oil dealing into the cylinder which is more than likely valve stem seals going bad from age. While you’re working on it may want to take a peak at the plenum and make sure it’s in good condition as well as that’ll cause smoke too

 

[GTyankee]

I have always been told that as long as there is not more than a 15% difference between cylinder readings, don't sweat it.

Of course when all of them drop down to some predetermined amount, it's time to rebuild or replace

 

[Dodge 1500 4X4]

Did you remove all of the spark plugs? It needs to have no resistance when cranking over, Also circled looks like a Dry test that will be lower and the numbers on the left are higher for a wet test indicating warn compression rings, also bad valve seals and worn valve guides will consume oil, have you done a leak down test?

 

[Octane]

Rebuild the heads

 

[crazzywolfie]

are you cranking till the gauge stops going up? those numbers are really low and the difference between the wet and dry test is minimal. if you cranked till the gauge stopped going up i would say you likely have a head issue. definitely might want to do a leak down test to help try and figure out where your issue might be.

Did you remove all of the spark plugs? It needs to have no resistance when cranking over

you don't need to remove all the plugs but it does help the battery last better.

 

[El Huapo]

I'm sure some will disagree but here's my thoughts:

Old school test if you pull the heads: if you can "catch" your fingernail on the ridge at the top of the cylinder, you probably should get it re-bored and new pistons, etc. A small ridge is OK.

Smoking mostly only on start-up is likely the valve seals. Tricky to replace with heads on but it has been done.

I broke down and did a valve job on my old 5.9 and felt embarrassed at how much better it ran afterwards, shoulda done it much sooner.

 

[CVX20]

Rebuild the heads

Be a waste at that mileage.Needs a complete build or just do valve seals and drive it.

 

[Daw14]

Old dates......".........

 

[crazzywolfie]

Be a waste at that mileage.

not necessarily. if that is the only issue with the truck it is likely worth it but they should do a leak down test first to verify how bad the heads or valves might be. also have to take into consideration that they are in Texas and not exposed to the salt and sand to make them rust out like they do in Ontario

 

[G-Ride990]

not necessarily. if that is the only issue with the truck it is likely worth it but they should do a leak down test first to verify how bad the heads or valves might be. also have to take into consideration that they are in Texas and not exposed to the salt and sand to make them rust out like they do in Ontario

Completely agree. Those numbers aren't bad enough to justify a full rebuild yet. I also think you might have a valve stem seal issue.