Afraid engine will become octane junkie

[RatFish]

I have a 2004 5.0L carbureted Mercruiser. The manufacturer recommends regular fuel (87 octane). The marinas in my area only sell premium fuel (93 octane). I had a car that suffered from this condition. Is there anyway I can lower the octane in the fuel I purchase or am I screwed?

 

[ThomWV]

Re: Afraid engine will become octane junkie

Look, folks need to understand this, the recommended octane rating is all you need to use but it won't do any harm at all to use a higher rated fuel. In a sense you already are using higher rated fuel anyway. You see, that sticker on the side of the pump that tells you the octane is actually telling you the minimum octane, not the exact or even the maximum. So it it says its 87 that means that it is at least 87 and could be anything higher than that.<br /><br />Also, there is no advantage what so ever to using fuel that is rated at a higher octane than recommended. It will not give you more power, it will not make the engine start easier, it will not somehow magically either make the engine run cleaner or somehow become cleaner internally. Every bit of that nonsense is pure marketing hype.

 

[BoatBuoy]

Re: Afraid engine will become octane junkie

ThomWV is absolutely correct. Octane is a measure of antiknock properties, not power. Back in the 60's I used to work at an airport, I ran a Volkswagon beetle on 200 octane aviation fuel. Ran OK but no stronger than regular pump gas. Valves didn't chatter though.

 

[cobra 3.0]

Re: Afraid engine will become octane junkie

You will not harm your engine with 93 octane. If anything it will keep your engine cleaner. It isn't magic. It's the extra cleaners that are usually put in into "super". And yes your engine will perform better if its under load with super. Any valve chatter is an indicator that the engine under stress is getting a little pre ignition/combustion. All you have to do is check your plugs and you will see much cleaner plugs if they were run on super.<br /><br />On my 3.0 they say in the manual to re-adjust the timing if the fuel isn't at least 89 octane(mid grade). I would inquire to find out if the timing can remain as is.

 

[JB]

Re: Afraid engine will become octane junkie

Moving to I/O

 

[Wart T]

Re: Afraid engine will become octane junkie

Well I don't know guys, He may have to wean that engine off the super stuff carefully. Some engines get attached to that stuff pretty strongly. To properly wean an engine off premium you have to start off by mixing in 1/4 tank of regular in with premium, then 1/2 tank in at next fill up, then 3/4 tank in, then full tank of regular. If it starts spitting, moaning, graoning, gets cold sweats, and wakes up in the night whining for "that good stuff" you might mix the next tank a little stronger. Older models tend to suffer more, but can be weaned quicker with a bottle of lead substitute. Don't try Lead substitute on newer models, they get addicted to that stuff after one bottle and only new valve seats will cure the cravings.<br />Once your engine is safely weaned off the premium a good 12 step wax program is recommended for the boat to help its self esteem. If you are ever caught in a situation where only premium is available go ahead and use it and then immediately begin the entire withdrawl process again. Explain to your boss and wife the importance of completing the 4 tank process as quickly as possible at your favorite lake. Get the kids and wife involved in the 12 step wax process making sure you properly supervise from a lawn chair mounted up in the back of a pick up for proper observation. Liquid refreshment is a must to keep the process flowing smoothly.<br />Now, if the engine never seems the same after completing the weaning and the 12 step program a new boat may be in order. The addicted boat should be sold with no mention made of its condition so it can start fresh with a new owner.

 

[tommays]

Re: Afraid engine will become octane junkie

well depending on the electronics package on the motor more so on a motor with EFI useing higher and lower octane fuels can drive the anti knock sensors crazy it is much less likely with a carbureted engine<br /><br />tommays

 

[Wart T]

Re: Afraid engine will become octane junkie

Yea, got to be careful about driving those knock sensors crazy...

 

[cobra 3.0]

Re: Afraid engine will become octane junkie

 

[RatFish]

Re: Afraid engine will become octane junkie

Thanks everybody for your comments. <br /><br />I was worried because I had a 1986 Toyota Pickup that was fed a steady diet of Premium fuel (93 octane) its whole life. I tried putting Regular fuel (87 octane) in it and it would ping like crazy. It was a 2.4L 4 banger with lots of miles (well over 100K) on it.

 

[Bondo]

Re: Afraid engine will become octane junkie

I tried putting Regular fuel (87 octane) in it and it would ping like crazy.

Because it Needed a Tune-Up.........<br />The Timing was Hot........<br /><br />It's Still got Nothing to do with the Gas Octane Rating..........

 

[RatFish]

Re: Afraid engine will become octane junkie

I see your point Bondo, thanks.

 

[BinLurkin]

Re: Afraid engine will become octane junkie

What Bondo said, the older the engine the lower the compression & the less octane it needs. Not more, like the gas company commercials tell us. As the engine accumulates miles & wears out the compression goes down.