Compression test 180 and 160

[Rustycycles]

Did a compression test on my merc 4.3 and all 5 cylinders read 180psi except for 1 cylinder which read 160-165 psi. Is this an acceptable difference? The boat also hasn’t been running for a while. Thanks for your input.

 

[bruceb58]

That's fine. 180 actually seems very high. This a good compression gauge?
I take it you had the engine warmed up right?

 

[Rustycycles]

That's fine. 180 actually seems very high. This a good compression gauge?
I take it you had the engine warmed up right?

Yes engine was warmed up. The tech didn’t seem too concern with this reading. I just wanted other opinions.

 

[mr 88]

As noted ,gauge is inaccurate. Reading should be no more than about 155 from the numbers I got when I googled the mercruiser 4.3

 

[Lou C]

Compression test results can vary for a lot of reasons, engine should be warmed up throttle valve open. Normally the 4.3 tests from 160-170 in my experience, but gauges can also be off. Mine has never been lower than 160 or more than 175. Carbon build up can also raise comp test results. As long as it runs well and does not miss at idle or burn oil I’d just run it.