Mercruiser 3.0 questions???

[cvbdrew]

Greetings,

I recently put 93 octane in my 3.0 because I was stupid and actually thought it would help with performance and clean out my old motor of any carbon build up. Only rather than help, it made it run worse... way worse. Once the 93 cycled through the old 87 in the tank I really started to notice it running poorly. Now I'm in the process of trying to get fresh 87 to cycle back through the tank. Unfortunately, I did my research after adding the 93 and found that it's bad to run a marine engine on higher octane than it was designed for. My question is did I hurt my engine by doing this? Total gallons of 93 octane that was actual put through the motor was about 10 gallons. The boat starts and idles normal, but when put under a load it starts to sputter and cough. I can cruise at low RPM's but when I try getting up on plane, it'll start to run rough... sometimes die.

The second problem I'm facing is with my outdrive trim. It goes up fine, but doesn't like to go all the way down unless I'm full throttle trying to get back up on plane. The force of the prop helps push it back down. Could this be the solenoid? Clogged pump or lines?

Any help is appreciated!

Thanks,
Drew

 

[Blaze5509]

Re: Mercruiser 3.0 questions???

My guess of what happened is the higher octane fuel does not detonate as easy so there is unburnt fuel. I don't think you can do much damage it just runs like crap. keep refilling her with the 87, run her low then refill again, repeat as neccesary.

The trim/plane problem I'll leave up to the experts

 

[Bondo]

Re: Mercruiser 3.0 questions???

Ayuh,.... Higher octane don't Hurt a thing,... It's just Wasting Money....
I'd sooner think you've got a dose of Water,....
Have you checked,+ replaced the Fuel Filters,..??

For the trim pump,.... Is there oil in it,..??
Is it running or Not,..??

 

[cvbdrew]

Re: Mercruiser 3.0 questions???

Ayuh,.... Higher octane don't Hurt a thing,... It's just Wasting Money....
I'd sooner think you've got a dose of Water,....
Have you checked,+ replaced the Fuel Filters,..??

For the trim pump,.... Is there oil in it,..??
Is it running or Not,..??

As for water in the gas....possible but probably not. The boat ran great prior to the higher octane. It was almost obvious that was the problem. I'm on it right now typing from my iPhone. Seems to be getting a little better.

The trim motor has oil and works. I hear it running when I trim up and down. It'll go down but only when moving. Barely goes down when not moving but rarely. I'm going to replace the down solenoid tomorrow. Worse case...it'll be a $20 guess. If the doesn't fix it I'll check the lines.

Thanks guys. Keep the advice coming!

 

[Bondo]

Re: Mercruiser 3.0 questions???

I hear it running when I trim up and down.
I'm going to replace the down solenoid tomorrow. Worse case...it'll be a $20 guess.
If the doesn't fix it I'll check the lines.

????????

Have the drive's pivots been Greased,..??

If you hear it Running,.... You might as well save the effort,+ just Burn that $20......

 

[cvbdrew]

Re: Mercruiser 3.0 questions???

????????

Have the drive's pivots been Greased,..??

If you hear it Running,.... You might as well save the effort,+ just Burn that $20......

Not recently. U think it's just a matter of lubercation?

The gas still seems to be an issue at high RPMs. Why would it run well at low RPMs and not at high RPMs???

 

[fat fanny]

Re: Mercruiser 3.0 questions???

You may have worked something lose in the carb (debree) or loss of fuel pressure go to the stickies and check out the great sections that will help diagnose your issues. Good luck!

 

[cvbdrew]

Re: Mercruiser 3.0 questions???

It's still coughing out when I'm above 3500rpms. When it does I can smell gas. Is that the unburnt higher octane?

 

[Bondo]

Re: Mercruiser 3.0 questions???

Is that the unburnt higher octane?

No,.... You have a Fuel Delivery Issue..... It might be the Carb, But it Ain't the Hi-Test gas....

 

[QC]

Re: Mercruiser 3.0 questions???

What he said ^^^^^

 

[bruceb58]

Re: Mercruiser 3.0 questions???

My bet is that it is a coincidence that it started because you put this gas in. You may have a little less power with the higher octane but that's about it.

 

[IVAZ]

Re: Mercruiser 3.0 questions???

Due to fuel availability I have switched from 87 to 93 octane more than once with no problems.
I would follow Bondos advice.

 

[alumi numb]

Re: Mercruiser 3.0 questions???

octane is just a rating for gas as cetane is for diesel, that's all.
the higher the octane rating the slower the fuel burns thus driving the piston down as compaired to flash hammering it down.
you can burn valves using to high of a octane rating.
the valve is closing and the fuel is still burning.
diesel burns slow so the need is there to speed the burn up.
the higher the cetane rating the faster diesel burns.
the higher the octane rating the slower gas burns.

 

[bruceb58]

Re: Mercruiser 3.0 questions???

you can burn valves using to high of a octane rating.

How is that possible? The valves are closed on both the compression stroke and the power stroke. The extra duration of the burn is not going to overlap into the exhaust stroke is it? Maybe if you were using very high octane like AvGas you would have to worry about it.

 

[QC]

Re: Mercruiser 3.0 questions???

Octane Rating is knock resistance, nothing else . . . You can run 120+ Octane natural gas in an unmodified gasoline engine except for the fuel system. Done all the time. Propane too at around 110 . . . Nothing to do with burn speed. Cetane yes, octane no.

 

[bruceb58]

Re: Mercruiser 3.0 questions???

Which is basically a controlled burn(higher octane) vs an uncontrolled burn.

 

[QC]

Re: Mercruiser 3.0 questions???

I like to say bang vs. burn . . . We deal with this a lot since we take a perfectly good diesel and then mess it up by injecting Nat Gas into the intake stream. As long as it doesn't bang it works pretty dang good.

The one exception to this Octane-doesn't-give-more-power-thing is that higher octane does allow you to advance the timing more and that can be a good thing. Octane still has nothing to with heat value (power). In fact, in the NatGas world, lower octane fuel usually has a higher heat value, sometimes MUCH higher and that leads to bangs more often than burns for two reasons: higher peak cylinder pressures and the low octane. Double whammy

Edit: also, for clarity, Octane and Cetane have literally nothing to do with each other except they both end in ane, like Methane, Propane, Ethane, Butane, and there's a whole bunch of other 'tanes. In fact Octane is a fuel, just became synonymous with Knock resistance because it is the standard in which knock resistance is based. Pure Octane has an Octane rating of 100.

 

[Rocky_Road]

Re: Mercruiser 3.0 questions???

How is that possible? The valves are closed on both the compression stroke and the power stroke. The extra duration of the burn is not going to overlap into the exhaust stroke is it? Maybe if you were using very high octane like AvGas you would have to worry about it.

We used to 'borrow' 115/145 aviation fuel...when I was flying, in the service.

It would burn the valves, if you didn't adjust your timing! It took awhile, though.

As for 93 octane burning any valves...it ain't gonna happen!

 

[alumi numb]

Re: Mercruiser 3.0 questions???

cvbdrew 10 gal's i doubt hurt a thing and as bruce stated it may just be a coincidence.
when i made my statement i already knew a herd of elephant's would be on stampede because of how techical these ratings are.
the majority think high octane contains more juice and for the layperson it's just a burn rating.
loss of power may be that you didn't harness all of the energy during the stroke and blew it out the exhaust.
pull a plug and check the color, could be carbon maybe.
did the fuel contain achohol, if so it may have picked up some water in the tank.
10 gal's shouldn't have hurt a thing engine wise.
don't know about the trim issue.

cetane is a alkane molecule that ignites very easily thus was used to assign a rating of 100 and alpha methyl naptholine was used to assign a rating of 0.
diesels burn about 75% of the fuel and nat gas is a catalyst used to help burn part of the remaining 25% thus more power.

for the man at the pump both octane and cetane are just ratings and a cetane rating of over 55 will do you no good.
now i'm nobody but i know a octane rating higher than the manufacturer assign's will also do you no good.

 

[cannonford57]

Re: Mercruiser 3.0 questions???

i'm going with the water thing.....just a coincicence that you got it with the 93....