3.0L mercruiser compression

[Finz123]

Hello, first off my boat is a 2005 SeaRay 175 sport with 3.0 mercruiser motor. Bought it last year, seemed a little slower on take of than I thought it should be and only get 4000rpm at wot without trim and 4400 trimmed. Just last week I took it to a repair shop to have them look at it and they said I have low compression. The numbers are 145, 150, 145, 145 then they told me it should be at 180. I did a search on compression and it seems like 145 to 150 is a decent compression for the engine, but maybe that is wrong. Question is what's a good compression for the motor?

 

[alldodge]

Find another shop, the 140 to 150 is golden
Look closer at your prop pitch

 

[alldodge]

Could throw it back at them
Tell them to build you a motor with 180 compression that runs on 87 octane with current prop and drive

 

[Finz123]

Find another shop, the 140 to 150 is golden
Look closer at your prop pitch

I dropped from a 19 pitch to a 17, sk feels a little slow off the bat

 

[Finz123]

Could throw it back at them
Tell them to build you a motor with 180 compression that runs on 87 octane with current prop and drive

They also claim i have lots of blow by

 

[alldodge]

They also claim i have lots of blow by

No way you have blow by with 150 psi, or their gauge is crap Hey @Scott Danforth

 

[Finz123]

They mentioned maybe stuck rings

 

[Scott06]

Find another shop, the 140 to 150 is golden
Look closer at your prop pitch

100% 150 is new , get a different mechanic.

Hello, first off my boat is a 2005 SeaRay 175 sport with 3.0 mercruiser motor. Bought it last year, seemed a little slower on take of than I thought it should be and only get 4000rpm at wot without trim and 4400 trimmed. Just last week I took it to a repair shop to have them look at it and they said I have low compression. The numbers are 145, 150, 145, 145 then they told me it should be at 180. I did a search on compression and it seems like 145 to 150 is a decent compression for the engine, but maybe that is wrong. Question is what's a good compression for the motor?

3.0 is a great motor for economy of ownership and reliability, not speed. Yes you should be able to get it to 4600-4800 rpm but that is probably prop related. When I had a 3.0 I ran a 16” prop for skiing etc , may need to drop in pitch.

 

[Scott06]

They mentioned maybe stuck rings

Again find a different mechanic. Ask them to show you the published compression numbers in the mercruiser manual, it’s 150 psi… please do not spend any more money with these guys have they verified your tach against a shop tach ?

 

[kenny nunez]

All 4 cylinder engines have what feels like “blow by” but it is really the result of the pumping action of pistons pushing air from the crankcase which is normal. With real “blow by” from worn or stuck rings there will be oil all over the top of the valve cover along with white smoke.

 

[Finz123]

Again find a different mechanic. Ask them to show you the published compression numbers in the mercruiser manual, it’s 150 psi… please do not spend any more money with these guys have they verified your tach against a shop tach ?

No i haven't verified my tach