High octane or regular?

[skimmer]

Just wanted to get a consensus of what everyones using in their older 2 strokes that used to run on leaded. I know that the unleaded is higher octane now but I've had differing opinions on whether or not to use the premium (higher octane) unleaded or just regular from the servo, when they first got rid of leaded they were recommending to boost the unleaded up with av gas, Not really necessary with the new unleadeds I guess but still, whats everyone using?

 

[WillyBWright]

Re: High octane or regular?

I don't recall anybody in the know ever recommending anything but regular. Everything else is rumor and old wives tales.

 

[steelespike]

Re: High octane or regular?

Most motors run well on 87 octane.Been boating 58 years have all ways used regular wheather leaded or unleaded.running high octane is a waste of money in a motor designed for regular.There are a few specific motors designed for higher octane.Had a friend with a 14 McCulloch the manual said to use 89
octane. I ran it on 87, ran excellent, he swore it idled and started better
on 90 octane the closest he could get to the 89.But he also tries all the gimmick add ons on his truck.

 

[GreatRiverDucker]

Re: High octane or regular?

What about the ethanol blended into regular?

 

[hkeiner]

Re: High octane or regular?

The Mercury authorized mechanic at my local boat shop strongly recommended to me to use premium gas with my motor. He said that pre-ignition/knock due to poor octane gas is a common cause of engine failures on the high horsepower 2-stroke outboard motors in California. He said that the regular gas sold in California often has poor octane qualities (something about one of the two octane measures being low and masked by the other higher octane measure). I am not a gas expert but I have been using premium gas without any apparent problem. The difference in cost is not that much so I figure what the heck...a small dent in my budget compared to other costs that I incur related to family boating.

I am not recommending or suggesting that anyone do what I do. I am just adding to the "consensus" discussion.

 

[WillyBWright]

Re: High octane or regular?

Mercury fuel recommendations
Everything you could possibly want to know about Ethanol and then some (from Mercury Marine)

What about the ethanol blended into regular?

Premium gas is the one most likely to contain ethanol, not Regular (some states require ethanol in all gasoline). Only a few major brands offer ethanol-free Premium (in states that allow it). Assuming most of Minnesota is like most of Wisconsin, Regular is just gas and everything above it has 10% ethanol. At least This year. Wisconsin will probably go to all grades with ethanol in the next year or two.

Alas, there are no concrete answers for every situation. Gasoline varies by municipality, region, nation, and brand. You need to do your homework and know exactly what you're pumping into your boat or you could end-up with serious problems.

For what it's worth (and to add to the confusion ), my car gets 37mpg with regular 100% gas and 34mpg with anything containing ethanol. It has a 12gal tank, so that ends-up being about an extra 36 miles per tank on Regular over Premium. Thought of another way, I waste a gallon per tank if I burn Premium. I burn a tank per week, so that would be a little less than a drum over a year (or over 4 tankfuls). So when I pay more, I get less. No Thanks!

 

[GreatRiverDucker]

Re: High octane or regular?

Thanks again Willy!

 

[Scaaty]

Re: High octane or regular?

What about the ethanol blended into regular?

I believe ETH has a very high anti-knock coefficient. You can run much higher compression on say E85.
That said..Octane is Octane. Reg back then was 87, today its 87. Lead was used then as an anti-knock agent AND to cushion the valves, which in a 2 stroke, last I looked, don't have any.
Only caution is a known fact I learned from a couple Merc Gurus on the older Merc Inlines though, because on the 6 cylinder crank layout, #3 was a little overtimed, so running 21 degrees, and mid-grade is the ticket here...and running a 1978 or above Trigger, with offset helps

 

[hkeiner]

Re: High octane or regular?

Not all gas with the same "pump" octane rating have the same octane characteristics. The octane rating number that appears on a pump at a gas station (say 87 octane) is really the average of two separate and individual octane ratings (RON and MON) of the gas. One octane rating (MON) is much more important than the other when it comes to what is needed for a high powered 2-stroke outboard motor. The less important octane rating can be higher than 87 and the more important rating (MON) can be lower than 87, bringing the average to an apparently good 87 but it may still be bad gas for the motor. I figure that by using a gas with a higher pump (i.e., average) octane rating (say 89 or above) will improve my chances that the important octane rating (MON) will be above 87.​

I am not providing this informatin to convince anyone to change their opinions on this subject. Just adding to the discussion. The following link contains more information about octane ratings than anyone would ever reasonably want to know.​

http://en.wikipedia.org/wiki/Octane_rating

 

[saltfisher]

Re: High octane or regular?

I have a 1988 merc 150 black max. Should i use higher octane? The previous owner said he ran 93 octane and it ran much better, and with lower octane he said it would "loose RPMs".

 

[skimmer]

Re: High octane or regular?

Thanks for the feedback guys, I guess theirs really no advantages unless your running a motor that requires a higher AKI (Anti Knock Index). From what i,ve read you can run it in any system that runs on unleaded without any problem and I must admit my engine does seem to Idle better and start easier on premium.

 

[gss036]

Re: High octane or regular?

I just had a discussion with a 20+ yr experienced mechanic, 2 days ago, and he said that he recommends premium to all his customers. That is the second mech that has told me that, but ,I still run regular gas as there is a 25 cent difference in price of the gas. So, it does add up and Merc recommends reg gas.

 

[Cape Coder]

Re: High octane or regular?

When I bought my bought the former owner told me to only run it w/ prem gas. I run it on 87 oct w/ 10% ethanol for for the last 2 yrs w/ no problems

 

[skimmer]

Re: High octane or regular?

Here,s a page from willys link showing mercury by year model (87-2001)only, fuel octane recommendations


http://www.mercurymarine.com/serviceandwarranty/mercruiserfaqs/fueloil.php

 

[pwiseman]

Re: High octane or regular?

Mercury fuel recommendations
Everything you could possibly want to know about Ethanol and then some (from Mercury Marine)


Premium gas is the one most likely to contain ethanol, not Regular (some states require ethanol in all gasoline). Only a few major brands offer ethanol-free Premium (in states that allow it). Assuming most of Minnesota is like most of Wisconsin, Regular is just gas and everything above it has 10% ethanol. At least This year. Wisconsin will probably go to all grades with ethanol in the next year or two.

Alas, there are no concrete answers for every situation. Gasoline varies by municipality, region, nation, and brand. You need to do your homework and know exactly what you're pumping into your boat or you could end-up with serious problems.

For what it's worth (and to add to the confusion ), my car gets 37mpg with regular 100% gas and 34mpg with anything containing ethanol. It has a 12gal tank, so that ends-up being about an extra 36 miles per tank on Regular over Premium. Thought of another way, I waste a gallon per tank if I burn Premium. I burn a tank per week, so that would be a little less than a drum over a year (or over 4 tankfuls). So when I pay more, I get less. No Thanks!

FYI Minnesota is not like Wisconsin on gas. Everything in your metro areas is 10% ethanol for all grades. You can get nonoxygenated gas in rural areas that is straight gas, and it is generally 91 octane. This is for offroad use though. No die in it like off-road diesel though and nobody says a thing if you fill the truck with it.

I tested millage on my 235 mile trip to the cabin with E10 on the way up and pure gas on the way back several times. 3 MPG is the difference I got in my F150 with the 5.4L engine.

Interesting if you look at cost per mile - say you have 87 grade E10 for 2.82 a gallon and 91 grade straight gas for 3.12 a gallon.

Ethanol 87
25 gallon tank * 2.82 per gallon / 15 miles a gallon = 4.7 cents a mile

Straight 91
25 Gallons * 3.12 per gallon /18 miles a gallon = 4.33 cents a mile

 

[Scaaty]

Re: High octane or regular?

FYI Minnesota is not like Wisconsin on gas. Everything in your metro areas is 10% ethanol for all grades. You can get nonoxygenated gas in rural areas that is straight gas, and it is generally 91 octane. This is for offroad use though. No die in it like off-road diesel though and nobody says a thing if you fill the truck with it.

I tested millage on my 235 mile trip to the cabin with E10 on the way up and pure gas on the way back several times. 3 MPG is the difference I got in my F150 with the 5.4L engine.

Interesting if you look at cost per mile - say you have 87 grade E10 for 2.82 a gallon and 91 grade straight gas for 3.12 a gallon.

Ethanol 87
25 gallon tank * 2.82 per gallon / 15 miles a gallon = 4.7 cents a mile

Straight 91
25 Gallons * 3.12 per gallon /18 miles a gallon = 4.33 cents a mile

Now ya forgot to add in the major increase in price for milk, eggs, cheese, (even coffee I bet), with the Ethonol fiasco...we have taken 2 steps forward, only it was a sand dune, and really fell back 8 feet..

 

[dhsbuckley]

Re: High octane or regular?

over here in australia things are different our lowest octane is 91 ron and premium is 95 or 97 for ultimate, i run a 1990 150 black max on 97ron which gives me a top speed of 67mph with a 22" prop against 91ron which the boat will only do 63mph on 91ron (gps tested and same fuel load) i have always been told not to run ethanol or 91 as there is a posibility of blowing holes in pistons at high revs.