Please help: Merc 3.0L sputter out of nowhere.

[Petamocto]

Hello everyone, I have used the search function and found some sputter-related posts but nothing that sounds like what I have.

I have a 1996 Sea Ray 175 Bowrider with the 3.0 Merc I/O. It has always been fully serviced and the engine looks brand new. It has ran perfectly all year so far.

Then yesterday I had it out towing a tube and all of a sudden it started making a loud sputter, almost like an old Model T or something, and power seemed to go down to 2/3 or 3/4 or so. It was out of nowhere, there was no build up to it.

The rate of the sputter goes up and down with RPM. All the gauge readouts seem to be fine (oil, temp, etc).

The only new variable was that I recently filled up the gas tank, but I tried letting it run for 1/2 hour to burn off some gas and it didn't change. Also, it was running for ~15 minutes before this happened.

I took a clip of it to hear the audio, I'll upload it soon.

Thank you for any tips.

Edit: Here is the clip I took to record the sound (click on photo, I think).



Or: http://s63.photobucket.com/albums/h143/SeanNewman/?action=view&current=BoatEngine.mp4

Also, I just got it back from one service shop (reliability unknown) saying that they diagnose it as a broken head gasket, also requiring some other gaskets like exhaust, with 6-7 hours of labour for a cost of $600-$700 repair total.

Sean

 

[bubbahemi]

Re: Please help: Merc 3.0L sputter out of nowhere.

The gas is one maybe the spark plugs or distributor also it could be the valves

 

[Bondo]

Re: Please help: Merc 3.0L sputter out of nowhere.

Also, I just got it back from one service shop (reliability unknown) saying that they diagnose it as a broken head gasket, also requiring some other gaskets like exhaust, with 6-7 hours of labour for a cost of $600-$700 repair total.

Ayuh,.... That sounds 'bout right,....

Be interestin' to see things torn down, before the clean up...

Ya wanta diagnose Why it blew, so's it don't happen agian....

 

[Petamocto]

Re: Please help: Merc 3.0L sputter out of nowhere.

Okay, thank you for the good advice.

I am the first to admit that I am not a marine engine expert though, so I don't really have much choice other than to take someone else's word for it.

Like I wrote, the only recently changed variable was filling up the gas but it was from a name-brand chain so I wouldn't think that would be it.

I don't beat it up or anything so it's not like I blew it from abuse. WOT is about 4500rpm so I normally scoot/cruise at about 3000-3500 because that's more than fast enough for me or to tow someone.

It would be great if they can identify what caused it, though.

 

[Don S]

Re: Please help: Merc 3.0L sputter out of nowhere.

I would think they would do a compression test and possibly partial leak down test to find out which cylinder it's on and if it's a head gasket or someting else. Maybe it's a valve blowing back through the carb, or an exhaust manifold gasket leak (if the gasket leak included the intake portion.
Or was the diagnosis more of a listen to it run and get an idea what it might be and a guess what the cost might be?

Did you look to see if a spark plug is missing???

 

[Petamocto]

Re: Please help: Merc 3.0L sputter out of nowhere.

Don,

Thank you very much for the reply. I think they did a compression test on it. They sounded pretty certain that it was the head gasket, but I have had mechanics sound certain of things before when it was just to rip me off.

6-7 hours of labour seems pretty crazy to replace a few gaskets (at least to me) when this engine seems so easily accessible.

 

[redneck_cdn]

Re: Please help: Merc 3.0L sputter out of nowhere.

Looks like you are on the right track, I had a neighbor flag me down last weekend on Friday night, He was taking the kids skiing and his Bayliner 3.0L Merc started popping with a louder exhaust sound from under the engine cowling. Upon further inspection we identified a blown intake/exhaust gasket on #2/3 cylinders blowing hot exhaust into the engine bay. We had the boat out of the water, in the garage with the manifold torn off, cleaned, check for true and re-installed with a new gasket (I had a spare from a top end rebuild on my 3.0L Volvo) torqued to spec ready to go back in the water in under 2 hrs. The manifold was still warm when we put it back on. The Merc/Bayliner was nice to work on with the two piece exhaust tube vs the 1 piece unit on my Four Winns.

Its a big job, but do not be afraid of it if you have decent mechanical skills, a good manual and time to do it right the first time.

I did a similar top end re+re on my 3.0l a couple years ago having the head gasket blow between #2/3 cylinders (internally), biggest problem I had was that I had to remove the cylinder head + exhaust manifold as an assembly due to clearance issues with the exhaust down tube on the boat. I took the cylinder head to the machine shop where they trued the surface and replaced the valves/guides seats ect as necessary, back on the boat , good as new.


Alex

 

[Silvertip]

Re: Please help: Merc 3.0L sputter out of nowhere.

Don,

Thank you very much for the reply. I think they did a compression test on it. They sounded pretty certain that it was the head gasket, but I have had mechanics sound certain of things before when it was just to rip me off.

6-7 hours of labour seems pretty crazy to replace a few gaskets (at least to me) when this engine seems so easily accessible.

The labor rate does not start when the first wrench is turned. The boat must be retrieved from the lot, put in the shop, engine cover and possibly some seats removed just to access the engine. Block is drained, valve cover comes off, manifold comes off as do any hoses/electrical that impedes head removal. Now the rockers are loosened, push rods removed, head bolts removed and head extracted. Parts are cleaned, inspected for cracks and cause of the gasket failure. See how this works?

 

[Petamocto]

Re: Please help: Merc 3.0L sputter out of nowhere.

Silvertip,

Thank you, but luckily I have brought it right to their shop and the boat I have is extremely easy-access. All you have to do to get access to the entire engine is popping off one engine hatch and you get this: