Fuel/octane questions

[Skeeter1993]

Need some help with the following. I searched through the old posts before I posted this so as not to be the stupid FNG. Now, I'm confused as ever, so I'll just ask the questions and pray for mercy.<br /><br />1993 Mercury 115 HP o/b w/ many hours bass fishing. I run it 12 months a year.<br /><br />1. I have run 93 octane for many years and all is OK. Will I screw-up if I go to 87 octane now?<br />2. Low speed idle is OK. Would it benefit the motor to de-carbon as some posts suggest?<br />3. Is there a down-side to running Sta-Bil in every tank of gas?<br /><br />Thanks,

 

[JB]

Re: Fuel/octane questions

Hi, Skeeter.<br /><br />Generally, most outboards require at least 87 octane and many Manuals recommend higher. Some actually require higher octanes, but only the Manual can tell you for sure.<br /><br />My general opinion is that the benefits of using higher than the required octane aren't worth the extra cost. I do run 92-93 in my Suzuki 4 stroke, but that is so that I can burn up left-over gas in my vehicle, which requires 91 or better. The Suzi only requires 87 (or better).<br /><br />Any 2 stroke benefits from regular decarbing. Carbed engines most of all. DFI engines can go longer than that and the E-Tec engines may go a LOT longer.<br /><br />I see no harm in Stabil-ing every tank of fuel, though real benefits are only there for long-term storage.<br /><br />You need Merc's requirements for your engine before you go to reduced octane. My guess is that 87 will be okay, but that is only a guess.<br /><br />Good luck.

 

[mellowyellow]

Re: Fuel/octane questions

too add to previous good advice... just how much<br />will you save by lowering octane? especially since<br />she's always drank the higher octane with no prob.<br />big risk? no. tiny risk? perhaps.<br />I just have a "superstition" that once motors<br />become accustomed to a certain fuel/oil mix and<br />they like it, to change is against the rules.<br />I even use the same brand name oil/fuel, but<br />that's a bit overboard prob.<br />good luck,<br />M.Y.

 

[LubeDude]

Re: Fuel/octane questions

This may sound like a contradiction to what I have posted in the past!<br /><br />I used to fish Bass tournaments with an 79 Ranger with an 85 HP Evenrude! You could find leaded premium then from union 76. Thats all I ever used in that engine along with synthetic oil at 80:1 Mix! Never decarbed and only changed plugs once that I remember! I tried the regular fuel once but didnt like the way it sounded so went back!<br /><br />Ive been posting not to use the more expensive, higher octane fuel because it will not burn as clean as 87 octane due to incomplete combustion, This is what I hear from the engine reps Ive talked to! I now use the 87 in my 150 Merc, along with synthetic injection oil!<br /><br />Ive not seen a problem with using the higher octane myself, but still beleive it a waist!<br /><br />Never done a test to see if there is an actual performance difference! Id have to say that I doubt if there would be!<br /><br />LubeDude

 

[JasonJ]

Re: Fuel/octane questions

I haved used 87 in everything unless specified otherwise. All octane does is suppress the burn, if you don't need the higher octane, you are just rolling up dollar bills and throwing them away.

 

[Skeeter1993]

Re: Fuel/octane questions

Thanks for the feedback. I'm kinda w/ mellowyellow on this. For a couple of bucks per tank, why not keep it like it is.<br /><br />Still up in the air on the de-carbon. If it ain't broke... But, will it improve performance?? Do I risk a new can o' worms??<br /><br />Later,

 

[JB]

Re: Fuel/octane questions

A properly done decarb will do no harm to your engine, Skeeter.<br /><br />If you wait for carbon buildup to cause problems it may be too late to fix it with a decarb.<br /><br />Regular decarbing is good and inexpensive insurance against expensive and extensive repairs.<br /><br />Good luck.

 

[WillyBWright]

Re: Fuel/octane questions

I know this will stir up a lot of debate, but you are actually damaging your motor by using 93 octane. The higher octane is accomplished by adding ethanol to regular 87 octane gas. Alcohol produces more carbon. So you're literally carboning-up your motor more than if you just used regular 87 octane gas.<br /><br />Alcohol also attacks most of the plastic and rubber parts in your fuel system, attracts moisture into your fuel tank, and worst of all...oil won't mix with alcohol well at all (especially if there's any water in the fuel), so you may be depriving your motor of proper lubrication.<br /><br />Your motor is designed to be run on 87 octane fuel. My advice is to NOT run 93 octane fuel...ever...for any reason. If it were a 4-stroke, my advice might be different. But premium gas is bad for 2-strkoes...all of them.

 

[jim dozier]

Re: Fuel/octane questions

WillyBright, not all oil companies use ethanol (ethyl alchohol) to raise the octane. I am sure that in some states in the US it may be done, but the pump will state so if it is. Usually, a variety of aromatic hydrocarbons are blended in to increase octane.

 

[BillP]

Re: Fuel/octane questions

Most of the high octane gas around my town doesn't have alcohol in it. Like jimd says, it is posted at the pump (at least in Florida it is) so you know.<br /><br />Skeeter1993,<br />My opinion is you should decarb at least every couple hundred hours. Some folks say "every 50 hrs" to "every season" so take your pick. It doesn't hurt the motor to decarb.<br /><br />Stabil...I don't know of any downside (however, I'm just a regular type guy with zero knowledge other that what Stabil advertises) but don't see the reason for running Stabil in every tank unless it sits long between uses. Long term to me is 6+ mos. That stuff is expensive and designed to keep fuel from going stale. Why do you want to use it if you boat year round?

 

[bluewater19]

Re: Fuel/octane questions

I used to work in the fuel business as a tranfer engineer.That being said the only reason the fuel companys put ethanol in gas is to meet requirments for emmisions. The alcohol does attack rubber and plastic and does attract water. The alcohol is used to introduce more oxygen into the fuel to help keep hydrocarbons down. The only by product of burning alcohol is water and nitrogen. The smog tech at the station used to tell me that if you have a motor that won't pass smog due to poor emissions add a gallon of denatured alcohol to a 1/4 tank of gas and it will clean them up long enough to pass the check. Anyway I belive that if your manual states use 87, then use 87 at a minimum. I doubt that using higher than required octane will harm a motor.How ever using less octane than stated in your owners manual states can cause detonation (pinging) and poor performance. If the motor is fuel injected the computer usually retards timing to stop the pinging and it kill horse power. on a carbed motor it just burns valves and pistons. I have a 2003 mercruiser v-6 that states you can use 87 only if 89 is not availible and that it will result in lost power. my 1991 mercruiser says 87 is fine. So thats what I run.