2016 Merc 300 XS. Don't have access to my serial number due to travel.
Question: Can I run 98 Octane Fuel in my engine?
The reason for my question is that I want to assure the quality of gasoline going into my outboard. If I buy fuel
one drum at a time I feel the quality can be controlled.
Carte's Custom
I would not run 98....
98 octane has to slow of a burn rate in a stock 300xs , it'll hurt the power.
Hmm, good info guys. What is the answere to finding fresh, clean, water free 93 Octane gasoline?
Carte's Custom
Mercury is saying use XX octane minimum. As in, higher is OK. Lower is not.
There is nothing in the owner's manuals that caution against the use of gasoline with a higher than specified octane rating.
The only thing that higher octane can do is to hurt ones wallet. Too low of an octane can kill a motor.
Rec 90 has no ethanol but higher than specified minimum octane rating. Many use it with no ill effects. Trying to stay away from the pitfalls that can occur with ethanol. Much is written about protecting oneself from gasoline with ethanol. Little is said about gasoline that has an octane that exceeds the minimum rating.
The minimum recommended octane will make the most power!
Originally Posted by jethro1
And common sense rears its ugly head LOL. It is amazing to me how these old wive's tales get started. There was a thread a while back where some were promoting the advantages of using 100% nitrogen verses 80% nitrogen, 20% oxygen in tires. Some may remember several years ago the dust up over synthetic oil. There was at least one major mfg (Harley Davidson) that strongly condemned the use of syn oil. One of its bad properties was that it was so slick that bearings would slide rather than roll as they are suppose to. There was a whole list of bad properties of syn oil. Above all never use syn oil in the first few thousand miles because the rings would not seat. S&S, the gold standard for air cooled V-twin engines now recommend pure syn from the first day. GM puts syn oil in at the factory for their Corvette.
Then we have the octane deal. As Jethro so accurately explains, the only harm is to the pocket book. If it hurt performance or cause damage you can bet that Mercury would point that out. Find me one example of Mercury Marine or Mercury Racing even hinting that using fuel with a higher octane than the MINIMUM required is detrimental to their engines. Well put Jethro.
Never said it was detrimental to the engine . A higher octane slower burning fuel then (required) in a low compression engine will not harm the engine but , it will make less power! Fact!!!
http://www.whitfieldoil.com/www/docs...p-racing-fuel-
If flame speed did decrease with increase octane number, it would wreak havoc with high RPM (high performance) engines. This information is available for those interested. It actually makes no difference in the context of outboard motors. It does no harm if some people think flame speed goes down with increase octane rating. As long as you use fuel that meets or exceeds minimum required for that motor it is all good.
And if higher octane reduced power I think Mercury would consider that detrimental, for sure Mercury Racing would.
Higher octane will be beneficial IF the 300XS has a knock sensor and IF it will continue to advance the timing until it reaches the level of sensing a knock and then retard the timing enough to eliminate the knock. Short of that you'll probably end up with an incomplete fuel burn leading up to increased carbon build up over time.
If it makes less HP, at what RPM? If only at WOT, and a user rarely runs at WOT, will the user even notice?
If it makes less HP below WOT, and the user just bumps the throttle up a tad to get to his normal cruise RPM and boat speed, will the user even notice?
Which is the lesser evil to a user? Lower octane gasoline with less carbon buildup but with ethanol added and the problems that can bring, or a higher octane gasoline with more carbon buildup over time, but with no ethanol?
Carbon buildup can be readily mitigated or eliminated with the use of certain gasoline additives or a decarboning procedure. That damn ethanol can wreck havoc without it being easily predicted.
I personally have never experienced an ethanol related problem. It's negative effects too can be mitigated with proper fuel treatment and fuel management. Unless the engine is engineered to and is capable of taking advantage of higher octane fuel it, higher octane, will provide no advantage and as noted in my previous post, can be detrimental to the engine. To the OP... Standard fueling recommendations still apply. High traffic stations that turnover inventory on a regular basis. However I do appreciate your predicament. Finding a station that sells high volumes of 93 octane could prove problematic.
Life is all about trade offs isn't it?
What works for one might not work for another. Or what does not work for one might work very well for another.
I ran three different four stroke model motors at WOT using first 87 octane and then using 93 octane. Thinking that if the higher octane burned slower I would be seeing less WOT engine speed and boat speed. Given that a slower burn rate would move the peak cylinder pressure to a later point in the piston position, similar to taking out some advance ignition timing.
If the higher octane burned slower I could not observe it in my engine tests. The engines were equipped with an exhaust gas temperature gauge. EGT values were the same with both octane types. One did not burn hotter or cooler than the other.
The more I read on the innerweb the less I understand.
If gasoline that meets the manufacturer's minimum octane rating does not cause knocking, why would you pay a premium for higher octane fuel? The higher the compression in the engine, the higher the octane needed. I'd trust the manufacturer to determine what's sufficient.
Because the OP has very legitimate concerns on the quality, freshness and true octane of buying pump gas in Texas and burning (who knows what) in one of these $20K motors.
I got that. But why wouldn't he buy a drum of 93, instead of 98? You seem to assume that lower octane rated fuel would be of lower quality, freshness and true octane than higher octane rated fuel. I don't care to make any assumptions in that regard.
Read the link provided about flame speed, octane rating and fuel grade. If octane rating is the sole controlling factor when controlling detonation why advance the timing on high compression racing engines???
Detonation is the act of combustion without a spark source. Advanced timing starts the combustion process in advance of the piston reaching TDC. I can accept that higher octane ratings will allow for higher compression w/o detonation but why start the ignition process sooner? Perhaps simply because of piston speed at high rpm's? I know detonation can occur at idle speeds so I'm not sold on the piston speed theory. This topic reminds me of one of my favorite quotes by Will Rogers. "What a man knows doesn't bother me. It's what a man "knows" that ain't necessarily so that has me concerned."
This is what I experienced in one season of running a 200 Pro XS on 89 octane. I was amazed at how much carbon was on the plugs. Maybe had something to do with breaking the engine in as well, but I will run 87 this season to see how that compares.
2017 Phoenix 819
2016 200ProXS, s/n 2B359849, Mod 1200P73BD
Reply With Quote