Reply
 
Thread Tools Search this Thread Display Modes
 
Old 07-29-2014, 09:57 PM   #1
Ensign
 
Join Date: Jul 2014
Posts: 3
Default 5.7 compression test- one cylinder at 150 psi, worry?

Doing a mechanical on a 2006 2600SE we are considering purchasing and the mechanic indicates cylinder 6 compression is 150 psi- all others 165. Is this a problem we should be worried about?
__________________

westcoastcalvin is offline   Reply With Quote
Old 07-30-2014, 12:28 AM   #2
Commander
 
Join Date: Jul 2011
Posts: 345
Default

In the cylinder that showed 150 psi, squirt a little oil, and re-test. If the psi changes, it could be a sign of leaking rings. If it doesn't, it could be either a bad head gasket, bad valves, or possible block problem. There shouldn't be more than a 10% delta across cylinders. These numbers are on the border.
__________________

jamanati is offline   Reply With Quote
Old 07-30-2014, 12:28 AM   #3
Lieutenant
 
Join Date: Sep 2012
Location: Watersedge Dundalk
Posts: 78
Default

they say that a 10% varience is ok
mrxitmt is offline   Reply With Quote
Old 07-30-2014, 01:26 AM   #4
Ensign
 
Join Date: Jul 2014
Posts: 3
Default

Quote:
Originally Posted by jamanati View Post
In the cylinder that showed 150 psi, squirt a little oil, and re-test. If the psi changes, it could be a sign of leaking rings. If it doesn't, it could be either a bad head gasket, bad valves, or possible block problem. There shouldn't be more than a 10% delta across cylinders. These numbers are on the border.
A number of mechanics have told me not too worry about it. The boat hadn't been in the water for a couple years. Plan to run it in the water and re-check. This make sense?
westcoastcalvin is offline   Reply With Quote
Old 07-30-2014, 02:54 AM   #5
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Essex, Maryland
Posts: 10,175
Default

Welcome aboard.

150 psi is considered a good compression. Low compression is lower than 130. The cylinder should be within 10%.

If anything is weak I would think a leak valve and not the rings with a reading this high.

Sounds like a good plan go me. Also check oil and gear lube after the run.
__________________
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2

Mike
mmwjr is offline   Reply With Quote
Old 07-31-2014, 03:57 PM   #6
Ensign
 
Join Date: Jul 2014
Posts: 3
Default re-test came up the same, 150 psi

Quote:
Originally Posted by mmwjr View Post
Welcome aboard.

150 psi is considered a good compression. Low compression is lower than 130. The cylinder should be within 10%.

If anything is weak I would think a leak valve and not the rings with a reading this high.

Sounds like a good plan go me. Also check oil and gear lube after the run.
After running the boat the re-test came up the same- 150psi. The boat only has 360 hrs on it, which seems low hours to start seeing a 10% vriance in cylinder compression, no?
westcoastcalvin is offline   Reply With Quote
Old 07-31-2014, 04:31 PM   #7
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Essex, Maryland
Posts: 10,175
Default

Engine build tolerances can result in a 10% variance right from the start. I would not be concerned. A gas engine typically last ~2000 hours so 360 is ~ 20% of the overlife.
__________________
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2

Mike
mmwjr is offline   Reply With Quote
Old 07-31-2014, 11:29 PM   #8
Lieutenant
 
njones's Avatar
 
Join Date: Jan 2010
Location: Decatur, AL
Posts: 53
Default

150 psi certainly sounds like a healthy cylinder to me. I wouldn't worry too much about it.
njones is offline   Reply With Quote
Old 12-13-2014, 04:16 AM   #9
Lt. JG
 
Join Date: Jun 2010
Location: winnipeg,canada
Posts: 32
Default

I wish I had 150 psi. My 1995 7.4 L has around 105 psi each. I then did a leak down test and they came in at around 8 % . I was ready to pull it out and rebuild it. Then I found a Mercruiser Service Bulletin from 1997 that said as long as they were above 100 psi all was good? Sure sounds low to me. It runs good. A little low on power for a 7700 lb boat. It ain't broke so unless I come into a bunch of spare money then I guess I won't fix it.
canada randy is offline   Reply With Quote
Old 12-13-2014, 01:13 PM   #10
Admiral
 
mmwjr's Avatar
 
Join Date: Feb 2012
Location: Essex, Maryland
Posts: 10,175
Default

Quote:
Originally Posted by canada randy View Post
I wish I had 150 psi. My 1995 7.4 L has around 105 psi each. I then did a leak down test and they came in at around 8 % . I was ready to pull it out and rebuild it. Then I found a Mercruiser Service Bulletin from 1997 that said as long as they were above 100 psi all was good? Sure sounds low to me. It runs good. A little low on power for a 7700 lb boat. It ain't broke so unless I come into a bunch of spare money then I guess I won't fix it.
How many hours are on it? What shape is the exhaust in? If the exhaust is allowing water to leak and it's get back to the engine burning water will damage the exhaust valves causing them to not seal properly.

However with all cylinders being low one would tend to think worn rings. So until the power is too low or she is puffing smoke I would hold off.
__________________
1997 Silverton 362, 7.4 Crusaders
1997 2400 SCR, 5.7 Vortec / Bravo 2

Mike
mmwjr is offline   Reply With Quote
Old 12-14-2014, 10:52 PM   #11
Lt. JG
 
Join Date: Jun 2010
Location: winnipeg,canada
Posts: 32
Default

Hours are unknown. No hour meter if you can believe that. I thought all boats had em. The leakdown test indicated any leakage was at the rings. She doesn't smoke. Runs very good actually. Just not as much power as I'd like. I had the exhaust apart to change the flappers and all looked good. Fresh water boat so it doesn't eat up exhaust like salt water.
__________________

canada randy is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 05:39 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2024, vBulletin Solutions, Inc.