1997 5.7 LX leak down test

[AKJohne]

I am concerned about the results of a cylinder leak down test I did today, ~ 172 hours on a rebuilt (others) motor.
Engine has closed cooling.

Test was performed with engine hot ~ 140F and cylinder PSI at 100
#1) 84
#3) 93
#5) 92
#7) 76
#2) 90
#4) 88
#6) 80
#8) 84

All leakage that I can determine is at the exhaust valves, no detectable leaks at the air horn, dipstick and no bubbles in the HE.

I decided to do this test as on my last outing I had to add ~ 1/2 gallon of coolant during 30 hours of use (much of it a trolling speeds), there is a recovery jug for coolant, motor was not overheating and I would check it in the morning and add some to the reservoir if needed.

Over the winter I resealed the mannies, risers etc as I had some issues there, I am 100% confident the prior coolant leak is now resolved. New hoses everywhere. Prior to the leak down test I performed a coolant pressure test and the system lost 3 pounds in a 24 hour period. no evidence of coolant in the bilge at any time.

I dont like adding coolant and was concerned about a possible head gasket even though that seemed unlikely.

The leak down test confirmed the compression test results I had done in the past, showing a slow degradation of the motor,
First test was done with 32 hours and showed 180 PSI on all 8. (cold motor)

Second test was done with 91 hours, also cold
#1) 175
#2) 174
#3) 173
#4) 170
#5) 178
#6) 160
#7) 160
#8) 167

Third test at ~ 140 hours hot motor
#1) 160
#2) 160
#3) 165
#4) 165
#5) 165
#6) 152
#7) 155
#8) 160

It is evident that we have two weak cylinders and have to believe the heads will need some attention before too long.
My initial reaction was to pull the heads, however Its a busy time of year and would like to put it off until winter, we will conceivable put 100 hours on over this coming season. Where we use the boat is 350 miles away, so we will tow and leave it in Valdez for the summer.

I think I am propped OK, using a 15.25 X 15 and will see ~ 4600 RPM at WOT. The boat is fairly heavy and will typically cruise around 3300 RPM.

Any advice is appreciated, Thanks, John

 

[tpenfield]

Leak test: Test was performed with 172 hrs., engine hot ~ 140F and cylinder PSI at 100
#1) 84
#3) 93
#5) 92
#7) 76
#2) 90
#4) 88
#6) 80
#8) 84

I think you have 2 fair/poor, 3 OK, 3 good, as color coded (red, yellow, green)

Compression test was done with 91 hours, also cold
#1) 175
#2) 174
#3) 173
#4) 170
#5) 178
#6) 160
#7) 160
#8) 167

Compression test at ~ 140 hours hot motor
#1) 160
#2) 160
#3) 165
#4) 165
#5) 165
#6) 152
#7) 155
#8) 160


Did you do the compression test when it was newer (32 hours), or was it someone else?. It is unlikely that all cylinders would be exactly the same (180 psi). If someone else did the test, the values may have been rounded up a bit.

I'd do a decarb with Mercury Powertune and see if your numbers come back a bit. You could also do a compression test with a cold engine to see if the numbers compare more favorably to the 91 hour test results.

#6 & #7 are definitely the lower cylinders on all tests.

 

[AKJohne]

I actually did the intial compression test, motor was cold and was rather shocked and pleased to see all the cylinders so close. We then decided to fire it up.

​https://vimeo.com/122218760?ref=em-share​​​​​

we bought the motor 2nd hand with 32 hours on it. Thinking the rebuild did not include "marine valves", maybe they are starting to tulip, maybe its common.... Question is, does it have another 100 hours in it before i have to fix? I wll have to look around for the merc decarb.