Need opinions on compression and leak down tests


LJ4ever

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Good Morning,

If anyone can help me make a decision on my test results I would highly appreciate it. Test was done due to a knocking with high miles (206k miles). It is a 2004 LJ with 206k miles but was well maintained by previous owner. Motor still has plenty of power, good oil pressure and water temp never exceeds 210. After reading numerous threads in what the knocking can be (piston slap/lifters/cam/bent push rod/ect....) I decided to share my test results in the hope that i can get a little help in making a decision to rebuild engine or just the head. I was amazed on the compression considering the miles.

Finished testing compression test and leak test, these were the results.

Compression ————--Leak down test-————————————-Air flow detected at:​
#1 165-———————--100psi in/ 88psi reading. 12%———--valve cover/oil dip stick​
#2 165-————————-/ 92 8%——————————————--valve cover​
#3. 160-———————-/ 82 18%——————————————-valve cover/oil dip stick​
#4. 168-———————/ 94 6%——————————————-valve cover​
#5. 170-———————/ 90 10%—————————————--valve cover/oil dip stick​
#6 160-—————/ 60 40%—————————————--valve cover/oil dip stick/exhaust​
 
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Chris

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The compression numbers look fine, though I'm not entirely sure how to read a leak down test. Maybe someone else can chime in on that.
 

pagrey

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When does it make noise? Have you checked the timing chain? I don't think compression or leak down is going to point to where your problem is unless you got some really crazy results.
 

CodaMan

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The way I see it is you have good compression, but may have a slight exhaust valve problem on #6. If i wasn't getting a misfire code for #6 I would leave it. What concerns me is you say there is knocking. Nothing in the head should cause knocking. Does the knocking speed up and slow down with RPMs? or does it go away with an RPM increase? Does engine temp make any difference on the knocking?
 
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LJ4ever

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When is starts up cold, the engine is real quiet, then about the 1 to 3 min mark the knocking comes. No codes are being displayed. The knocking slow down, I believe under acceleration, but hard to hear over fan. at idle is when you really can hear the knocking. Sounds like a diesel at idle.
 

Goatman

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Under normal conditions compression will mostly indicate ring condition. Leak down mostly valve condition. The #4 and #6 are off. Possible very small head gasket issue. Very, very small. And I agree the knock is what is concerning. With no other indicators (oil pressure, codes, fouling plugs) I would be hesitant to act on that comp/leak test. I would run some Mystery oil or Diesel to try and clean up any varnish or sludge before pulling the engine apart. And try to locate better where the noise is coming from first.
 

CodaMan

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When is starts up cold, the engine is real quiet, then about the 1 to 3 min mark the knocking comes. No codes are being displayed. The knocking slow down, I believe under acceleration, but hard to hear over fan. at idle is when you really can hear the knocking. Sounds like a diesel at idle.

That really sounds like a lower end (piston, rod, wrist pin) problem.
 

pagrey

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Your description sounds a bit like a rod knock. I'd strongly recommend the checking the timing chain, it can mimic that and is really easy to check and replace. The rod, not so much.
 
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LJ4ever

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Wow, I forgot to mention, i apologize, this all occurred after an oil change. Oil change with 10w-30 / Mopar filter.
In reference to timing chain, wouldn't it make clacking noise instead.
 

pagrey

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Wow, I forgot to mention, i apologize, this all occurred after an oil change. Oil change with 10w-30 / Mopar filter.
In reference to timing chain, wouldn't it make clacking noise instead.
Nope, low knock, the camshaft bounces around at idle and sits just about level with the pistons in the block. It does not rattle at all.

Edit: not at all suggesting it is likely, just really easy to check and there is a small chance that is it
 

pagrey

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If it started after the first oil change it is possible the previous owner had used some really thick oil to mask a problem. You might dump the 10w30 and get some 15w40 or 20w50, couldn't hurt if the temps aren't too low where you are.
 
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LJ4ever

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can that mask timing chain noise, yes I tried 15w-40 even used Lucas, but same issue. This why I posted cause Im confused. Idles great, runs strong, no codes, regular temps and oil great pressure
 
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CodaMan

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My OCD would never allow me to let it go plus, I would always be worrying about it giving up the ghost at the worst possible time.
 
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LJ4ever

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That’s what I was leaning towards but I have left the engine without running for a few days, so I know that the oil has drained to the oil pan. On start up I can hear the ticking of the valves then it goes away when the pressure goes up
 

pagrey

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can that mask timing chain noise, yes I tried 15w-40 even used Lucas, but same issue. This why I posted cause Im confused. Idles great, runs strong, no codes, regular temps and oil great pressure
The oil wont change the chain at all. Have you connected an oil pressure gauge? The factory dash gauge is fake.