Compression psi?

Sterling · Feb 24, 2017

I have a 2001 5.9 with 167000. I need to replace the plenum gasket and valve seal seals because I'm burning oil. I'm sure the cat is probably clogged by now too. Not much in parts but hours of labor. The head gasket appears ok, at least passed the blue fluid test. Before I get started I'm going to check the compression. What would be the expected psi. If they are all close what would be the cut off before I just replace the motor? I know this is subjective but I'll take opinions

dodge dude94 · Feb 24, 2017

Minimum is 110psi with a 10PSI variation between cylinders.

Sterling · Feb 25, 2017

Thanks

rod7515 · Feb 25, 2017

I just did a compression test on my 5.2 with 183k on it. They ranged from 140-150 in all 8. You may also want to do a cyl leakege test before making a decision. I just did that as well. That will tell you if you have ring, head, valve train issues. With both sets of information you can make a bettter decision.
Rod

crazzywolfie · Feb 25, 2017

anything over 100psi on a compression test is ok but you probably do want to see at least 150psi or so across all cylinders. my 81 sits at about 170psi accross all cylinders. just make sure to hold the throttle open when cranking the engine over. also you may want to make sure to do both a dry and wet test especially if you are getting low compression numbers.

i would agree with rod tho. a compression test is a cheap and quick way to check an engine but a leak down test is a more thorough way to see if there is any issue with rings or valves

Sterling · Feb 26, 2017

Thanks for all the info. I was pretty happy with 1-7 getting around 140, except 5 which was 125,but 8 was 60. Ugh!

Not sure if it's a head issue or ring issue or if matters. I'll probably limp it along. I guess I'll fix the plenum so it runs as good as possible.

Any recommended long blocks?

crazzywolfie · Feb 26, 2017

did you do a wet test on cylinder 5 and 8? that would let know if your issue was with the rings or the valve.

Sterling · Feb 26, 2017

Not yet. Is there any recommended oil to use? I've heard use atf because it has a lot of cleaning agents, 20w-50 oil because it's thick and sea foam because breaks down carbon. Any recommendations?

dudeman2009 · Feb 26, 2017

For soaking the rings during a compression test, any oil will work, whatever the cheapest oil you have is. You only want to put a little in, a bottle cap worth is enough.

If the pressure rises quite a bit, then the rings are gone, if not the valves are leaking or the head gasket is bad. To tell if its the headgasket or not, check your coolant, if its disappearing or mixed with oil/black soot its the head gasket. If not, its possible the head gasket is still bad, just not as likely. Another possibility is leaky valves, but you cant really test those without pulling the heads.

If that cylinder is bad and pressure won't go up, there is really nothing you can do besides rebuild it. either partially or fully.

crazzywolfie · Feb 26, 2017

i have heard water works pretty good to get rid of carbon in the cylinders when used like sea foam. i don't know if it is true or not. as far as engine oil goes i prefer to run shell rottella 15w40. it has a whole bunch of diesel truck additives that will help keep the inside of your engine clean.

dudeman2009 · Feb 26, 2017

crazzywolfie said:
i have heard water works pretty good to get rid of carbon in the cylinders when used like sea foam. i don't know if it is true or not. as far as engine oil goes i prefer to run shell rottella 15w40. it has a whole bunch of diesel truck additives that will help keep the inside of your engine clean.

Water will work like seafoam. To properly clean the carbon with water, take the truck for a decent drive to get it warmed up, then slowly sip water either into the intake, or through a vacuum line while at high idle.

Compression psi?

Sterling

Junior Member

dodge dude94

Millennial Boomer

Sterling

Junior Member

rod7515

Member

crazzywolfie

Senior Member

Sterling

Junior Member

crazzywolfie

Senior Member

Sterling

Junior Member

dudeman2009

Senior Member

crazzywolfie

Senior Member

dudeman2009

Senior Member

Similar threads

Latest posts

Staff online

Members online

Forum statistics

Share this page