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Do you follow the fuel recommendations in the Indmar manual?


28 members have voted

  1. 1. I fuel my 1994-2002 Indmar with:

    • 87 Octane
    • 89 Octane
    • 91 Octane
    • 93 Octane

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According to the 1994-2002 service manual, we're supposed to put 89 octane (or higher) in our engines; to wit:

All carbureted and standard EFI engines run on unleaded fuel of 89 Octane (R+M)/2 or higher. The LS1 requires 93 octane or higher. Fuels must meet the specification ASTM D4814 in the US and CGSB 3.5-92 in Canada. These fuels need no additives.

I've been putting in 87 octane, and that's all they sell at some of the lakes I frequent. I haven't noticed any ill effect. Any comments or opinions? (In my Volkswagen if I put anything under the 91 octane specified in my manual I get a lean condition, which is why I am asking this question.)

Edited by slap
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My Monsoon is still under waranty. Let's just say if I used 87 octane my engine would run like a champ. If I really used 87 octane I would run a tank of 91 octane now and then just in case there is fuel injector cleaner in that blend as claimed.

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The ECM will manage the timing to allow for running any octain, that is part of its programing. It is also why knock sensors are so important in newer motors.

The required rating is for power ratings purposes. the motor may make better power with a higher octain of at least it is guarenteed to make within a caertain percentage with the recomended fuel. Now if you are worried about fuelinjector cleaner run a little seafoam through it a couple times a year.

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I stubbornly fueled my boat with 87 Octane at the start of this season and my 320 Monsoon didn't seem to like it. I started having weird hesitation problems when the rpms climbed above 2000. Switched to 89 octane and all has been good since. IMO they tell you 89 octane in the manual for a reason. Yes the ECM will adjust timing etc. to accommodate but these engines are made to run with what they specify in the manual.

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I usually haev no choice except 87 at the marinas. Some have 91, so I do a blend, but many only have 87.

When I fuel at a gas station, I use either Shell or BP 89 octane.

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I have always followed the manuals recommendations. Just assuming you fill up once a week for 52 weeks at twenty cents a gallon more than the price for 87 octane, that's $364.00 a year. A small price to pay for keeping the engine happy.

Edited by LS-One
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We always run 87, There are alot of variables that determine what octane fuel to run, but as said earlier the computer will manage for lower octane fuel if there is an issue. With these motors only being 9.4to1 compression ratio, I don't have an issue running 87oc fuel, combined with the low operating temps I cant imagine ever having any issues. I am a firm believer in more octane is not always better, and have proved it on a dyno. Higher octane has the capability to make more power, but doesn't mean your going to make more power by running higher octane fuel, and in most cases will actually loose power. I believe this subject has been beat to death on the forum before.

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Mine runs noticeable stronger with 89 over 87. I ran 87 for many tanks until I realized it wanted 89. When that knock sensor retards the timing, you are going to lose power....

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