Compression test values - JeepForum.com
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post #1 of 34 Old 08-19-2019, 04:14 PM Thread Starter
Alex_
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Compression test values

Hello again everyone; I have posted here before about my grand Cherokee 2007 having some issues specially with overheating and losing power to injectors 1 and 2 the later was fixed but the overheating started happening shortly after and there's also a consumption of coolant but no puddles on the floor.

So pretty much I did a compression test and this are the values:

Dry (4 cranks)

Cylinder 1= 135
Cylinder 2= 130
Cylinder 3= 135
Cylinder 4= 132
Cylinder 5= 145
Cylinder 6= 130
Cylinder 7= 140
Cylinder 8= 134

Dry (6 to 8 cranks, until the gauge was not going up anymore)

Cylinder 1= 160
Cylinder 2= 150
Cylinder 3= 170
Cylinder 4= 159
Cylinder 5= 163
Cylinder 6= 145
Cylinder 7= 150
Cylinder 8= 150

Wet (on the lowest cylinder cranked 6 to 8 times until the gauge was not going up anymore)

cylinder 6= 165
cylinder 2= 162


what I observed on the 6 to 8 cranks test is that there is delta of 25 psi, which from what I understand that is no good (or am i wrong?) and when the compression test was done wet on cylinder 6 and 2 the values went up.

what im wondering with this if it could be a piston ring or a head gasket since I dont know what else I can do to diagnose where the coolant is going or the engine is overheating but less than before.

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post #2 of 34 Old 08-19-2019, 07:41 PM
Smith3973
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Im guessing for the wet test you put about a tablespoon of oil in the cylinder? If the wet test has more compression than the dry unfortunately that means your rings are worn out
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post #3 of 34 Old 08-19-2019, 08:32 PM
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I just had an over heating problem with my 07 hemi & a loss of power but couldn't find any leaks.
bottom line, I removed the water pump & found the impeller had come unfastened from the pully shaft there fore there was no coolant flow. replaced the water pump, coolant temp came back to normal & power levels came back. didn't run a second compression check.
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post #4 of 34 Old 08-19-2019, 08:39 PM Thread Starter
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Quote:
Originally Posted by Smith3973 View Post
Im guessing for the wet test you put about a tablespoon of oil in the cylinder? If the wet test has more compression than the dry unfortunately that means your rings are worn out
That would be correct, one tablespoon onto the spark plug holes; so it seem to be pointing to the rings, I was thinking it could also be a head gasket leak.
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post #5 of 34 Old 08-19-2019, 08:43 PM Thread Starter
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Quote:
Originally Posted by nvrdone1 View Post
I just had an over heating problem with my 07 hemi & a loss of power but couldn't find any leaks.
bottom line, I removed the water pump & found the impeller had come unfastened from the pully shaft there fore there was no coolant flow. replaced the water pump, coolant temp came back to normal & power levels came back. didn't run a second compression check.
I had a broken water pump impeller, the water pump was replaced along with the thermostat and the radiator hoses; now it can keep cool longer but I had a few instances where I'm almost at redline with no explanation possible or 1/4 past the middle temp gauge mark.

Also when doing the compression test, I inspected the spark plugs and they look terrible for some plugs that don't have more than 2000 km, some seems to have some oil and other seems to be rusted looking.
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post #6 of 34 Old 08-19-2019, 08:57 PM
Chris Radley
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Can you post any pics of said spark plugs so we can see?
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post #7 of 34 Old 08-20-2019, 07:18 AM Thread Starter
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Originally Posted by Chris Radley View Post
Can you post any pics of said spark plugs so we can see?
Absolutely, as you can see on the picture I don't even think this spark plugs have 1000 km they dont even have 2 weeks of being installed and they already look like that.
Attached Thumbnails
plugs 1.jpg   plugs 2.jpg  
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post #8 of 34 Old 08-20-2019, 08:22 AM
RCS1300
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Good test. Great results so far.

To objectively pin point the issue you will need to perform a leak down test. It requires compressed air and a gauge. There are several videos on youtube about how to do the test and the test is not difficult to perform. The test will definitively tell you if you are losing compression on the rings, the valves, or the head gasket by where the air is escaping.
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post #9 of 34 Old 08-20-2019, 09:26 AM Thread Starter
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Originally Posted by RCS1300 View Post
Good test. Great results so far.

To objectively pin point the issue you will need to perform a leak down test. It requires compressed air and a gauge. There are several videos on youtube about how to do the test and the test is not difficult to perform. The test will definitively tell you if you are losing compression on the rings, the valves, or the head gasket by where the air is escaping.
I was thinking of doing one but I will need to take it to a place that can do it since I don't have access to a leak down tester or an air compressor.

From what I'm gathering from the test, the compression values are not that bad for an engine with 265.000 km, it does looks healthy in terms of psi but the 25 psi difference between cylinder 6 and cylinder 3 makes me think from what I been reading that there is a leak somewhere what im not that sure is if its the rings or head gaskets.

I think 150 psi across most cylinders is not bad but then again its a 20 psi difference between them and I think the threshold is 10% of the higher compression cylinder (I may be mistaken) so around 17 psi difference.

I was starting to think than on cylinder 6 and 2 since I only performed the wet compression test went up by quite a bit that It could be pistons 6 and 2 rings and maybe the head gaskets in general too since In the picture in a post above, the spark plugs are brand new, they don't even have 1000 km and they look corroded and some have oil in them.

Thinking of machining and resurfacing the heads since apart from the leak down test don't know what else to do; the machining, resurfacing, chemical bath and machining the valves if any is damaged and can be recovered is around 160$ in my country which I don't think is that bad; of course I would also have to source the valve stem seals, the head gaskets, any damage valves and correct me if I'm wrong but I think once you take out the timing chain you cannot reuse it, I'm not sure on that one.
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post #10 of 34 Old 08-20-2019, 09:49 AM
RCS1300
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My suggestion would be to perform a leak down test and then decide new re manufactured engine or engine repair or new vehicle. The timing chains, all three of them, should be fine. But when I replaced my engine heads at 85,000 miles due to a sticking valve I also did the timing chains. Did all the work myself.

The cause of the overheating issue is what you are chasing now, I think. Need to solve that problem.
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post #11 of 34 Old 08-20-2019, 09:59 AM Thread Starter
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Originally Posted by RCS1300 View Post
My suggestion would be to perform a leak down test and then decide new re manufactured engine or engine repair or new vehicle. The timing chains, all three of them, should be fine. But when I replaced my engine heads at 85,000 miles due to a sticking valve I also did the timing chains. Did all the work myself.
I think I will be going with the engine repair route, I will also look on who can perform the leak down test; the reason I'm going to repair it is because in my country (Venezuela) is easier to get the spare parts shipped via courier than a complete re-manufactured engine (which can be stolen in customs and is too flashy) due to shipping cost and the insurance I would have to pay on it.

the engine honestly is not in bad shape the only issue is the overheating that is happening at the moment, since switching the water pump is less but sometimes I almost reach redline or 1/4 past the middle temp gauge.

Vehicle prices over here are weird, things don't depreciate with time, they go up in the used automotive world; a guy was asking 20.000$ for a 2010 toyota fortuner which is ridiculous, another one was asking for a grand cherokee 2013 60.000$ so a new vehicle at this point is out of the question; you can find cheapo cars sub 20k and sub 10k but they usually have issues that needs repairs or are older than 2010.
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post #12 of 34 Old 08-20-2019, 10:04 AM
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Originally Posted by Alex_ View Post
Absolutely, as you can see on the picture I don't even think this spark plugs have 1000 km they dont even have 2 weeks of being installed and they already look like that.
It good that the plugs look similar, except for the one, oil-wet looking plug. The motor is aged , of course, so things will start to go wrong.

Coolant doesn't disappear, unless you have a leak, or the motor 'eats' it. You haven't found a leak, so that means water is being consumed by the motor. Usually a head gasket, but sometimes a crack is the culprit.

The 'leak down' will pinpoint the likely cause of cylinder variation, and MAY also identify a head gasket problem. Leave the radiator open during the tests. Compression usually backflows into the radiator via the 'blown' area.

Arranging your data into banks of 1,3,5,7 and 2,4,6,8, I don't really see a significant inter-cylinder variation that would scream "Blown Gasket'. A crack can lose water into the chamber and NOT affect some tests, as the crack often 'closes' after cool-down, and may not be detectable that way.
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post #13 of 34 Old 08-20-2019, 10:12 AM
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Originally Posted by gutthans View Post

Coolant doesn't disappear, unless you have a leak, or the motor 'eats' it. You haven't found a leak...
Keep in mind that it is possible that coolant is leaking from the heater core and not visible. You would probably smell it, but do not assume it is the engine until you can test the engine to prove it is or is not.

Given that you plan to repair the motor a leak down test is the next best step to find the source of the leak and likely the cause of your over heating issue.
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post #14 of 34 Old 08-20-2019, 10:16 AM Thread Starter
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Originally Posted by gutthans View Post
It good that the plugs look similar, except for the one, oil-wet looking plug. The motor is aged , of course, so things will start to go wrong.

Coolant doesn't disappear, unless you have a leak, or the motor 'eats' it. You haven't found a leak, so that means water is being consumed by the motor. Usually a head gasket, but sometimes a crack is the culprit.

The 'leak down' will pinpoint the likely cause of cylinder variation, and MAY also identify a head gasket problem. Leave the radiator open during the tests. Compression usually backflows into the radiator via the 'blown' area.

Arranging your data into banks of 1,3,5,7 and 2,4,6,8, I don't really see a significant inter-cylinder variation that would scream "Blown Gasket'. A crack can lose water into the chamber and NOT affect some tests, as the crack often 'closes' after cool-down, and may not be detectable that way.

Really? I would have thought a 25 psi variance was a big difference pointing to a leak somewhere either blow gasket and maybe piston rings; now that you said it, a crack on the heads or the block could also be an issue that I cannot visually inspect, hopefully the leak down test can pin point more of the engine issue.
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post #15 of 34 Old 08-20-2019, 10:18 AM Thread Starter
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Originally Posted by RCS1300 View Post
Keep in mind that it is possible that coolant is leaking from the heater core and not visible. You would probably smell it, but do not assume it is the engine until you can test the engine to prove it is or is not.

Given that you plan to repair the motor a leak down test is the next best step to find the source of the leak and likely the cause of your over heating issue.
that's another interesting theory, don't know how to check the heater core though and I'm not smelling any coolant. my next step on this week is find someone that can perform the test since I don't have the tools for it.
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