3.0 L Mercruiser Compression Test Result Question

[harleysilo]

1989 3.0 liter Mercuriser in a Celebrity I/O 19.5 ' cruiser....

So 5 years ago when we had some issues we took our boat to a mechanice, who replaced a lot of small parts, changed the oil, outboard gear lube etc. Part of his inspection included a compression test. He has since retired and all of the information that I have is....

#1 134 psi
#2 102psi
#3 116 Psi
#4 125 Psi

I thought I read that they are suppossed to be 140 psi...

Granted this is a 5 year old test, the boat has maybe seen the lake 20 times since then, and would only have probably <10 more hours of operation since the test.

How bad is my number 2 cylinder

 

[Robj]

Re: 3.0 L Mercruiser Compression Test Result Question

If the numbers were that weak then, they are probably worse now. Based on those numbers, I think it is rebuild time. Plus why are you posting results from 5 years ago, are you experiencing some engine problems now? It would be of more value if you did another compression test and posted those numbers along with any problems that you are experiencing.

Have a great day,

Rob.

 

[harleysilo]

Re: 3.0 L Mercruiser Compression Test Result Question

Yeah I'm currently having an issue getting the engine to start, we are also just trying to determine in general what we want to do with the boat. I realize those numbers are old.

The rear area floor is now rotten, not sure how much damage until I remove part of the floor, could be all ruined or just the surface. Don't know if the motor is mounted to wood, fiberglass covered wood or what, or if that important piece is rotten as well. Whole interior could be recovered etc.

We typically just drive the boat from the ramp to the closest vacant island, beach it and hang there the rest of the day swimming and playing with the dogs. We don't generally ride up and down the lake all day pulling skiers etc. So that's why we've kept the boat so long, can't "ruin" it cause it's already so crappy and with 3 dogs it doesn't take much to ruin a boat.....

 

[Robj]

Re: 3.0 L Mercruiser Compression Test Result Question

Hard starting can be explained by low compression, but there can be other reasona as well. The real bad news is that if the floor is soft, so may your stringers, and transom. You should check out the entire boat before planning on how to proceed. Replacing stringers, floor and stringers is a big job. I know I am just about finished replacing mine. Good winter project if your wife will let you do fiberglass work in your garage.

Good luck and have a great day,

Rob.

 

[harleysilo]

Re: 3.0 L Mercruiser Compression Test Result Question

Rob,

Do you have a thread somewhere documenting your work on the floor and stringer job?

I was quoted around 5 grand if I was to bring in the boat and have them do the entire job, they said it would be between 50 and 60 hrs. at $90 hr. I would consider having them pull the engine and just do the transom and leave the rest to me but really have no idea whats involved....

Got pictures?

 

[harleysilo]

Re: 3.0 L Mercruiser Compression Test Result Question

How difficult is it for me to perform the compression test, I assume I need a guage that screws in a sparkplug hole....