89 vs 88 octane

KOKANEE · Nov 6, 2012

Hi guys. My boat calls for 89 octane or higher. I found some ethylol free gas at 88 octane. Will dropping down to 88 octane harm my motor or even make that much difference? I like the idea of pure gas but worry about octane ratings. Please hlep.
Brent

SuperD · Nov 6, 2012

You will be fine but could always add a little octane boost if you were too worried. Someone that I trust in these matters actually told me that lower octane is better when operating our boats at elevation such as where you reside and higher. High octane fuels are subject to pre-ignition in thin air at high altitude. The lower octane fires more efficiently and completely.

Paul S. · Nov 7, 2012

If it's an inboard engine, it shouldn't make a bit of difference. If it's a two stroke outboard, you might richen the oil a bit in the premix. I do this as a matter of fact as most of my operations are between 4500-7000 ft elevations. Also, a half ounce per gallon of fuel of marine grade Stabil in the tank won't hurt whether it's a four stroke or a two stroke engine.

KOKANEE · Nov 7, 2012

Its an inboard 5.7 320hp and the trolling motor is a 4 stroke mercury 9.9hp. I guess its 87 octane at the pump not 88 as I originally quoted. Does this change anything?
Brent

Paul S. · Nov 8, 2012

Shouldn't make any difference. .I'd still use the marine grade Stabil in both of 'em. Better yet, drain the fuel tank(s) if it's going to sit all winter without being used and replace with fresh stuff come boating season again. Even the non alcoholic gas seems to break down a bit after it's sat for a few months, not as bad as the alcohol added stuff but we don't get the same quality of gas we did years ago.

Kokaholic · Nov 8, 2012

I prefer to fill my tanks for the winter with new fuel and additive. I m not a fan of leaving them empty due to condensation that builds in the tanks, along with running all of that dry allows for gaskets and such to dry out and crack. But, thats what I do. Doesnt mean that these other ways wont work for you.

lowe1648mt · Nov 11, 2012

Kokaholic said:
I prefer to fill my tanks for the winter with new fuel and additive. I m not a fan of leaving them empty due to condensation that builds in the tanks, along with running all of that dry allows for gaskets and such to dry out and crack. But, thats what I do. Doesnt mean that these other ways wont work for you.

I agree. Plus with a full tank you get a lot less rust or corrosion in the tank. Check with a dealer. No reason you could not add some 2 cycle oil to the full tank to hold down corrsion. Always change the fuel filter at the end or beginning of the year.

89 vs 88 octane

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