91 Octane?

[Ron Burgundy]

Found some Evinrude FAQ here on this subject.
http://www.evinrude.com/en-US/Owners-Ce ... dFuel#qst3

Excerpt from this article...


What grade of fuel should I use in my motor?
Current recommendations are to use a minimum of 87 octane, 89 octane is preferred. There is no additional benefit from using higher-octane fuels, in fact they may cause hard starting conditions in hot weather.

Dosen't say 91 will harm the motor, but will not be of any benefit as others have stated. You might find this thread interesting...viewtopic.php?f=2&t=8584&hilit=+fuel

[Kim in FL]

Thanks, guys.

Yeah, I read the FAQs as well as the other threads here on the forum. That's why I was still a bit confused about the effect of the higher octane. I'll have to email Evinrude this week for more info, especially regarding warranty. I assumed there wouldn't be a significant benefit to using 91 over the recommended 89, but that's all my marina offers. Most of the boats there are way more expensive than mine, so perhaps that's why they sell it. Who knows? $4/gal is expensive, although it's only $.20 more than I pay for 93 octane w/ethanol for the car.

Maybe I'll get better performance, but will settle for no adverse effects ("hard starting conditions in hot weather" .... I'm in FL ... Oh well) or issues with the warranty. I'll let you know what Evinrude says.

Appreciate all of the input.

[Rounder610]

Let me start with: I am not a chemist. This is my basic understanding of octane ratings and what that means to your motor.

An octane rating is basically a measure of how much heat and press the fuel can take before it will ignite without a spark.

Different motors are built with different compression rates or, how much they compress the fuel and air in your cylinder before your spark plug fires.

A motor rated for 87 is a low compression motor. A motor rated for 91 or better is a high compression motor.

Using fuel rated below your motor's rating can have negative performance effects and can actually cause damage to the motor because the fuel can be compressed the the point where it ignites before the spark plug fires, effectively ignoring your motor's timing cycle by creating the pressure that will ultimately force your cylinder head down before your motor is ready for it. You can hear this happen and it is usually referred to as a 'ping'.

Using fuel that is rated higher than your motor is rated for does not have the same issue. In a motor rated for 87, 87 octane fuel will not ignite until the plug fires. 91 octane in that same 87 rated motor will also not ignite until the plug fires. So you are in exactly the same spot with 87, 89, 91 or even 95 octane race fuel.

Also note that your manual should say 87 or better, 89 or better or 91 or better. They are giving you a minimum octane rating.

Labeling 87 'Regular' and 91 'Premium' is a marketing gimmick that is effective in selling fuel they charge more for with little justification.

[belercous]

I've worked on engines since I was 13 and have been an FAA certified aircraft mechanic since 1984.

Rounder has it right. Higher octane will not harm an engine, or at least 91 octane won't hurt an 87 octane rated engine. Problems can occur if one starts running avgas in a low compression engine since avgas contains a lot of lead which will build up in the combustion chambers, and has been known to burn the valves out of the old VW engines. (The lowest octane rated avgas sold today is 100LL which is the equivelant to 130 octane automotive. It goes up from there. Many older piston engine aircraft require higher octane as they are supercharged, these are radial engines mostly.)

Higher octane does not make an engine run richer. Higher octane rated gas will not make an engine run cooler, but it will allow an engine to run hotter before detonation occurs. (And just as a matter of trivia, there is no octane in gasoline. Octane is only a rating comparing heptane [0 octane] to iso-octane [100])

If the 91 octane gasoline is 100% pure (no ethanol) the engine will perform better (both power & mpg) as gasoline contains more btus/gal. than alcohol, but it won't make it run smoother. One can get away with running lower octane gas if the engine is not run hard and the manifold pressure is kept low, but if you don't know what you're doing, don't try it. (Detonation is the "pinging" sound valves make when a (4 cycle) engine is under a heavy load. If you ever hear this, ease off the gas as it is hurting the engine. On 2 cycle engines the sound will be much worse.)

[Kim in FL]

Rounder, Belercous,
Thanks for the additional detailed explanations.

[GXPWeasel]

I love educated, to the point, and fact based answers.

[Kim in FL]

I finally got around to calling Evinrude and speaking with a technician. He said there is absolutely no problem with using 91 octane and there are no warranty issues. They list 87 octane because most people (understandably) want to use the cheapest fuel allowable.

Thanks for your input.

[DonCabo]

I have a 2012 E-Tec. Most marinas sell 89 or 91 and upcharge $1/gal.

My solution is I bought three 5 gal gas cans, go to the gas station and fill them up.

Go to your local Bass Pro (or order online) and buy a shake-siphon: http://www.basspro.com/EZ-Siphon/produc ... 4/-1746926

It was the best $7 I've ever spent. My marina has carts that I use to lug down the 3 gas cans, I put the gas can on the sunpad above the fuel intake, shake-shake-shake and it pumps fast. 2-3 minutes and she's drained.

You'll save a lot of money not buying gas at the marina.

[Kim in FL]

Just checked out the site. At $7, it might not be a bad idea to buy one for my hurricane kit as well. Less messy when trying to fill the generator.

[DonCabo]

Just checked out the site. At $7, it might not be a bad idea to buy one for my hurricane kit as well. Less messy when trying to fill the generator.

Funny, I have 10 5-gal cans that I brought with me to NC from FL. I lived in Fort Lauderdale for a few years and needed those cans for my generator like you! They came in handy. After filling up my SUV and the 10 5-gal cans, I was like a rolling napalm bomb going up I-95.

[GregF]

I went the other way on my generator. I got a tri fuel kit so I can run it on gasoline, propane or nat gas.
Propane is the attractive one since I have a 150 gallon tank buried in the yard with a spare hookup right where the generator goes.

[belercous]

Thanks Don. I've been trying to find one of them for the last 2 years. They work great. They've been out for well over 20 years and they still aren't ubiquitous. This siphon hose is a "must-have" item.

[ROLAND]

This thread got me wondering what Yamaha recommended as far as fuel grades for thier 4 strokes... so I started looking thru the manual...and for the life of me I can't find anything about fuel grades, only problems with fuel & ethanol. Anyone know what grade you should use in a yammy F 75. I've just been running regular / 87 octane. Should I be running 89 or higher?

[belercous]

If the engine was "detonating" under a load at W.O.T., then you're ok.

Detonation is the "pinging" sound valves make, as in an older car going uphill under high throttle settings. The pinging sound is caused by the fuel mixture igniting too soon causing the valves to slam shut. The engine is being hurt when this happens.
If you're over 40 years old chances are you've heard it. It doesn't happen much today as car engines are fuel injected & computer controlled.