# What's the best gas for a mercury motor



## Woody24

A friend of mine were discussing gas when we went out last 
He said that his mercury motor says to use 87 and not 93. I always 
Used 93 premium bc I thought it was the best gas for my motor. He has a 
2012 mercury and I have an 81. What do u guys use?


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## whodeynati

I bought my boat brand new in 2011. It has a 115hp Mercury 4 stroke. The dealership told me to use regular unleaded (87) all the time.


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## bludog

I have a 86 9.9 Merc and I usually run 89 octane because my truck needs it. I don`t think you can go wrong following what Merc says.


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## bountyhunter

I have four motors ,they seem to run better on 89.


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## fastwater

Have always run mine on manufacturer recommendations without issue.


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## allyfisher

You did not say what your 1981 motor is. Some of the older motors were higher compression and need the higher octane. Especially if it is the old straight six tower of power.


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## Woody24

It's a mercury 150 xr2 pervious owner put on the boat
Premium only by the two gas tanks


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## creekcrawler

Seeing as how all my outboards are antiques, or at least pretty old, and I'm running a older IH Cub Cadet and ancient David Bradley tractor, all my tanks are 93 octane for the older engines.
Chain saw guy swore that it was better to run either Shell or Mobile.


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## Gottagofishn

This thread ran on Walleye Central a while ago. Someone on there pointed out that the Merc. manual says "at least 87 Octane" (I haven't checked to verify that). They went on to state that newer engines are designed to give the best performance for what you put in it. That is to say, you might get marginally better performance out of a higher octane... If all of that is true.

That being said.... I have run 87 in mine for two years and it seems to be doing fine. (150 4s)


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## allyfisher

The XR2 is a high performance motor. I would think premium is going to be a must. It is a small price to pay to keep one of those alive.


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## Bad Bub

The higher the octane, the slower and cooler the fuel will burn. High octane sometimes will not burn completely in motors that are not designed for it. Always follow the manufactures recommendations. They've put way more hours into testing fuels than all of us combined.


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## K gonefishin

I run 89 in my pro xs premium is a waste imo


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## SaltyHD

I run 93 octane in my '02 200 Optimax and '02 9.9 4stroke and have never had any trouble in either. I run 93 in everything I own clear down to the weedeater. Was told by an engineer friend that 93 burns cleaner (less soot) and requires less fuel for operation. Have used the same for many yrs. I would think 93 would only make it more efficient.


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## Bad Bub

Here...
http://www.nicoclub.com/archives/gasoline-octane-myths.html


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## ssv1761982

I found this on Scream and Fly. Detonation is the main worry on one of these. You should also make sure it is propped to turn 6,000 rpm. This was the hotrod engine of the day in the mid 80's. No comparison to today's Pro XS or other hi tech screamers.

From Scream and Fly:
a few facts.

#1 the 1985 xr2 that i have out back had 130 lbs on all cylinders plus or minus 1-2 lbs. that is with 2 weekends a month of use on a bass boat from the time it was new untill 2 months ago. all original parts other than water pump and plugs/wires.

#2 Xr2 motors are by nature a little more high strung than a 150 horse 2.5 or 2.4 litre. therefore demanding more resistance to detonation.

#3 the original manual for the XR2 reccomends premium fuel.

#4 the updated factory tech service maunal also states that only premium unleaded fuel should be run through the xr2 and the mag 1 (mariner xr2) 

As for octane. octane helps to prevent detonation, but it ALSO helps the fuel atomize better. go ahead and run whatever octane you want, its your motor, but i dont want to hear you bitching when you discover a hole burnt in the #6 piston because you wanted to save 7 cents a gallon on gas.


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## Woody24

I guess that sums it up thanks guys


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