Do i need to be concerned about these compression numbers yet

T

Tmakaro

Seaman
Joined
Nov 22, 2011
Messages
66
hi, I just did a cold compression test on my 4.3 mercruiser. I couldn’t warm the engine up because my manifolds are currently off. The motor is a 2010 with 560 hours on it.
here are my numbers
1 = 145
3 = 150
5 = 178
2 = 183
4 = 175
6 = 180
seems to idle fine
 
M

Mc Tool

Petty Officer 1st Class
Joined
Aug 7, 2024
Messages
312
Numbers 1 & 3 dont look so good , and they are next to each other so maybe head gasket leaking between the two.
Has it been sitting for a while ? I would do a hot comp test after you have run it a bit before reading to much into it .
 
tpenfield

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,137
I usually look for numbers in the 5-10% range of deviation from the 'norm', which in this engine appears to be 175-180 psi. So, yes, #1 & #3, are a bit out of range.

A cylinder leak test would be my next step.

Most engines will idle and even rev-up just fine, despite any issues.
 
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