Afraid engine will become octane junkie

RatFish

Chief Petty Officer
Joined
Jul 29, 2003
Messages
647
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

Senior Chief Petty Officer
Joined
Dec 19, 2003
Messages
701
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

Rear Admiral
Joined
May 29, 2004
Messages
4,856
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

Lieutenant Commander
Joined
Jul 31, 2003
Messages
1,797
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

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Afraid engine will become octane junkie

Moving to I/O
 
Top