What octane do you use?

Newer 8.1s with electronic fuel management modules are set up to run on 87 octane. Some manufacturers say to avoid higher octane fuels unless 87 is not available. Paying for premium gas on engines set up to run on 87 is a waste of money.
 
Actually, all Merc. stern drives have an 87 octane fuel requirment even into Merc. Racing power with the the HP525EFI. Starting with the HP600SCi you step up to 91 octane but from there on up they are SCi's. At the 1200 you leave the pump for higher octane.

Of course most custom power is build for power, so if it's a pump gas motor, usually NA and of always with SC it's 91+ octane.
 
When you say pre-ignition are you talking about it not shutting down right away? I've heard it refered to as dieseling, not that it's the proper term....anyway mine does that if I come off plane and shut down, when picking up a skiier/wakeboarder etc...,

Some call it pre-ignition, run on, or dieseling. As far as dieseling when you pick up a wakeboarder, just shut it off when its in gear.
 
Sorry I thought it was covered in Dave and Jeremy's posting in the link but here is what the Mercury Manual of your boat says.

Page 40

Fuel Requirements:
Important - Use of improper gasoline can damage your engine. Engine damage resulting from the use of improper gasoline is considered misuse of the enngine, and damage caused thereby will not be covered under the limited warranty.

Fuel Rating - Mercury Mercruiser engines will operate satisfactorily when using a major brand of unleaded gasoline meeting the following specifications:

USA and Canada - having a posted pump Octane Rating of 87 (R+M)/2 minimum. Premium gasonline [92 (R+M)/w Octane] is also acceptable. Do NOT use leaded gasoline.

It goes on to talk about using reformulated gasolines and gasolines containing alcohol.
I just purchased a previously owned '93 Sea Ray Overnighter Mercruiser v8. Unfortunately without a manual and can't find one anywhere. Any chance you could readers digest what it says about gasolines containing alcohol?
 
You didn't ask but I'll chime in on what is likely to be a controversial point. If your motor is tuned for 87, there is absolutely positively zero benefit to using a higher octane. Well, no benefit to the buyer anyway. That said, it won't cause any harm to do so, other than to your wallet.

This is discussed relentlessly on the hot-rod forums.
 
Wicked old thread but always nice to have a throwback party.

General consensus amongst the boaters I run with is that ethanol is the child predator of the boating world. Don't let it on or near your boat, don't turn your back on it and for sure don't let your kids get too close to it.

Hey MIEric, fill your boat up at the marinas in Michigan and you'll get ethanol free mid-grade or premium. It's spendy but why tempt fate with that evil ethanol :)
 
Fresh e10 at my local gas stations that gets refilled every couple days for $2.89. Or non ethanol gas that’s been sitting in the tank for who knows how long for $3.54? I’ll take the e10. The evils of 10% ethanol gas have been waaay overblown! Just my opinion of course.
 
Fresh e10 at my local gas stations that gets refilled every couple days for $2.89. Or non ethanol gas that’s been sitting in the tank for who knows how long for $3.54? I’ll take the e10. The evils of 10% ethanol gas have been waaay overblown! Just my opinion of course.

Just make sure you're diligent in changing your fuel/water separators :)
 
Any octane that is "Non-Ethanol" is what goes in my tank.
 
I just purchased a previously owned '93 Sea Ray Overnighter Mercruiser v8. Unfortunately without a manual and can't find one anywhere. Any chance you could readers digest what it says about gasolines containing alcohol?

RD version, It says nothing about gasoline containing alcohol. It was not a thing then.

No vessel built before 2011 has alcohol resistant fuel system. The critical parts are rubber parts that seal in carburetors and fuel injection systems. Alcohol dissolves rubber, it is just a fact. Fuel did not commonly contain alcohol before 2007 when the law was passed putting it in fuel for road use.

E-10 has base gasoline that is typically 3 octane less than what is on the pump. The alcohol is high octane and provides the rest of the advertised octane. E-10 begins deterioration in 90 days vs. gasoline at 1 year. Not good to have in sitting in boat fuel tanks.

Avoid alcohol containing fuels like the plague

MM
 
Fresh e10 at my local gas stations that gets refilled every couple days for $2.89. Or non ethanol gas that’s been sitting in the tank for who knows how long for $3.54? I’ll take the e10. The evils of 10% ethanol gas have been waaay overblown! Just my opinion of course.


The owners of marine repair shops, particularly in day boating areas where gas station fill ups are common, say differently, they report that fuel system issues have exploded with E-10 use. Far more fuel system components must be replaced on vessels that ran fine for years but after using E-10 fuel they had major issues.

The folks that perpetrated this on us think of this as a feature, not a bug. It destroys older boats and outboards getting them off the water and forcing owners to buy newer equipment the government regulates...

MM
 

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