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Author Topic:   Octane requirement for 225 HP Ocean Runner
Lopaka posted 03-22-2004 01:52 PM ET (US)   Profile for Lopaka   Send Email to Lopaka  
Is 87 octane suitable for use in my 225 hp Johnson or should I use 89 and if so, why?
macfam posted 03-22-2004 06:01 PM ET (US)     Profile for macfam  Send Email to macfam     
I think the manual for the 96 225hp calls for a minimum of 87 octane. Any "John-rude" dealer can tell you.
I use 87 all the time with no problem. I do however ALWAYS use the recommended fuel conditioners.
For my yamaha, I use "ring-free", and with my Johnson, "2+4 fuel conditioner" (or something like that).
These conditioners are supposed to continuously keep "carbon buildup" at a minimum.
I use top quality oil(usually the manufacturers brand)....period.
I've had Johnsons, Evinrudes, Mercs and Yamahas. Never had a problem.......never had a repair........never.
jimh posted 03-22-2004 07:59 PM ET (US)     Profile for jimh  Send Email to jimh     
Generally the owner's manual for an engine make clear what the require fuel is for proper operation. I would go by that.
Smallfrye posted 04-01-2004 09:42 AM ET (US)     Profile for Smallfrye  Send Email to Smallfrye     
Considering that with the rising cost of fuel, the manufacturers will want the octane level on the lower end of the tolerance, I use 89 octane Chevron fuel. This includes the "conditioners" mentioned(Techron). Subjectivly; the moter seems to run smoother.
My outboard mechanics, both have rebuild shops, recommend 89 octane fuel with some type of conditioner. They also recommend synthetic oil to reduce carbon build up.
Bigshot posted 04-05-2004 02:47 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I run 89 for the simple reason that the fuel today loses octane points real quickly. That 87 you put in might be 85 in a couple weeks. If 87 is MINIMUM, I would sure hate to run 84 a month later. Before gas was $2 a gallon, I ran 93 in my 225 Ocean runner, now I run 89 and see no difference.
rbruce posted 04-11-2004 10:35 PM ET (US)     Profile for rbruce  Send Email to rbruce     
The higher the octane number the farther spark timing can be advanced as the fuel mixture will hold its own and not explode at an unplanned stage (detonation or pinging) during the compression cycle.

This is specially valid in motors that regulate ignition timing. Some automotive motors take advantage of these feature of gasoline not only by having higher compression but also detonation sensors that will retard spark if detonation is detected. I do not know if this is applicable to marine motors.

But if your motor is not optimized for 89 octane, then you are wasting your leisure dollars and probably increasing consumption as higher test gasoline burns much slower than lower test engine.

To conserve the quality of your fuel you should use fuel conditioner and restorer before storing and even using it to curtail water corrosion and gums and varnish deposits.

This information should be in your owner's manual and you should be able to get one from a dealer for your motor.

mustang7nh posted 07-09-2004 05:53 PM ET (US)     Profile for mustang7nh  Send Email to mustang7nh     
is there every any problem with mixing octanes? For example, 87 this tank, 93 the next, 89 the next and so on.
whalernut posted 07-09-2004 10:30 PM ET (US)     Profile for whalernut  Send Email to whalernut     
What does it say for a 1975 85hp Johnson. i am curious as I don`t have an owners manual. Thanks-Jack.
Bigshot posted 07-11-2004 10:15 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
No problem with mixing octanes I do it all the time.

Jack...gas was of higher quality back then and most outboards ran on regular "leaded" fuel which is roughly 89 octane.

stefan posted 07-23-2004 10:03 AM ET (US)     Profile for stefan  Send Email to stefan     
I was using highest for my johnson'83 140 (highest octane at pump -93?-i'm having a brain cramp this a.m.)
manual said minimum is 91 octance for this year/HP
my neighbor who has had rude/johns all his life and has owned fish camps etc... said to use lowest -87 cause higher octance causes engine to run hotter.
For lower HP motors book said that's right -lowest octane,
but I'm thinking I should stick w/ what book says.
I'd rather use 91 than 93, but only choice seems to be either 89 or 93

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