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

 

[Scott Danforth]

Inline spec was 145-150

Verify your gauge and fire your "mechanic". (In quotes for a reason)

How old is the fuel?
Check how clean the spark arrestor is
Check if the flapper dropped

 

[Finz123]

Inline spec was 145-150

Verify your gauge and fire your "mechanic". (In quotes for a reason)

How old is the fuel?
Check how clean the spark arrestor is
Check if the flapper dropped

When I last ran it last season the fuel was fresh. I haven't had the boat out hat as they're is still some ice on the lakes. Spark arrestor is clean. Not sure what flapper your talking about

 

[Pmt133]

There is a flapper in the exhaust near the rubber boot after the elbow to help prevent water from back flowing. They sometimes break off and clog the lower exhaust.

While I have seen good compression with high leakdown tests... that doesn't sound like what is going on here. You can test the leak down if you like but at that even of compression I doubt it's the issue.

Like was said, verify tach, check the basics and find a new guy. 19p on a 17 foot boat is probably about right... I ran a 19 mirage on my 19' cuddy with a 3.0l and was in the rpm range even loaded. 17 was better for water sports but not needed. When you went from the 19 to the 17 prop, did you gain RPM or not?

 

[Scott06]

No i haven't verified my tach

worth doing as in dash tachs tend to drift over time. if its off you may be hitting correct WOT rpm already.

 

[Finz123]

There is a flapper in the exhaust near the rubber boot after the elbow to help prevent water from back flowing. They sometimes break off and clog the lower exhaust.

While I have seen good compression with high leakdown tests... that doesn't sound like what is going on here. You can test the leak down if you like but at that even of compression I doubt it's the issue.

Like was said, verify tach, check the basics and find a new guy. 19p on a 17 foot boat is probably about right... I ran a 19 mirage on my 19' cuddy with a 3.0l and was in the rpm range even loaded. 17 was better for water sports but not needed. When you went from the 19 to the 17 prop, did you gain RPM or not?

I can't remember what my numbers were but I did get a small increase. I think 1 or 200 ram. My friend has a 2001 bayliner 17.5 ft with a 3.0 mercruiser and a 17pitch prop and his boat seems to preform better than mine. Better take off and top speed

 

[airshot]

Fuel from last year is no longer fresh unless treated with fuel stabilizer. Dealer should have verified your tach before testing. I would get my money back from them !

 

[airshot]

Bayliner will weigh less, much cheaper built boat.