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Compression test results?


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Old 01-05-2018, 12:24 PM
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Compression test results?

So, the compression test results for the truck Iím looking at came back ranging from 142-154 in the cylinders. Is this good, bad, so so? I would think not great. Shouldnít they all be within 5psi of each other. The shop also said there was a small coolant leak coming from the back of the engine but couldnít tell where from. Thoughts on this?

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Old 01-05-2018, 04:41 PM
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Coolant leak might be from the heads. Mine started leaking because the back two head bolts were loose. Easy fix. Not sure on the compression
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Old 01-05-2018, 04:49 PM
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15% max between cylinders is allowable. This is a basic industry standard. I start to worry once 10%+ is reached.
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Old 01-05-2018, 09:34 PM
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They are low results period. Did they have TB open?
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Old 01-05-2018, 09:37 PM
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Just curious what should compression numbers be?
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Old 01-05-2018, 10:35 PM
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Quote:
Originally Posted by VENOMOUS1 RACING View Post
They are low results period. Did they have TB open?
Iíll ask the shop and get back to you. Anything else to ask? I know they did it cold so that could effect it as well
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Old 01-05-2018, 11:54 PM
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Originally Posted by IronAffliction View Post
Just curious what should compression numbers be?
In a good sealing engine 175-180 never less then 170 unless rings are worn and it'll be sustantially lower. Leakdown test is just as important !
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Old 01-06-2018, 10:34 AM
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This is from Page 5519/8410 of the OEM Service manual for our trucks...

CYLINDER COMPRESSION PRESSURE TEST
The results of a cylinder compression pressure test can be utilized to diagnose several engine malfunctions.
Ensure the battery is completely charged and the engine starter motor is in good operating condition. Otherwise the
indicated compression pressures may not be valid for diagnosis purposes.
1. Check engine oil level and add oil if necessary.
2. Drive the vehicle until engine reaches normal operating temperature. Select a route free from traffic and other
forms of congestion, observe all traffic laws, and accelerate through the gears several times briskly.
3. Remove the Auto Shut Down (ASD) relay from the Power Distribution Center (PDC).
4. Disconnect ignition cables from spark plugs.
5. Remove all spark plugs from engine. As spark plugs are being removed, check electrodes for abnormal firing
indicators fouled, hot, oily, etc. Record cylinder number of spark plug for future reference.
6. Be sure throttle blade is fully open during the compression check.
7. Insert compression gauge adaptor Special Tool 8116 or the equivalent, into the No. 1 spark plug hole in cylinder
head. Connect the 0-500 psi (Blue) pressure transducer (Special Tool CH7059) with cable adaptors to the scan
tool. For Special Tool identification, (Refer to 9 - ENGINE - SPECIAL TOOLS).
8. Crank engine until maximum pressure is reached on gauge. Record this pressure as No. 1 cylinder pressure.
9. Repeat the previous step for all remaining cylinders.
10. Compression should not be less than 689 kPa (100 psi) and not vary more than 25 percent from cylinder to
cylinder.
11. If one or more cylinders have abnormally low compression pressures, repeat the compression test.
12. If the same cylinder or cylinders repeat an abnormally low reading on the second compression test, it could
indicate the existence of a problem in the cylinder in question. The recommended compression pressures
are to be used only as a guide to diagnosing engine problems. An engine should not be disassembled
to determine the cause of low compression unless some malfunction is present.

So, it looks like your fine especially if it was performed cold.

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Old 01-06-2018, 03:21 PM
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Quote:
Originally Posted by Aavt View Post
So, the compression test results for the truck Iím looking at came back ranging from 142-154 in the cylinders. Is this good, bad, so so? I would think not great. Shouldnít they all be within 5psi of each other. The shop also said there was a small coolant leak coming from the back of the engine but couldnít tell where from. Thoughts on this?
depends on how they did the test, but sounds like you are in the range of all being the same, ive seen low an high readings, our gauges show 160-180 but have seen other gauges show low
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Old 01-10-2018, 11:41 AM
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25% WOW. That is high MA Mopar. Shame on you
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