Fuel-high octane vs. low octane

[gator]

What grade fuel do you run through your motor? I've heard those who run a low octane fuel called idiots by those who only run high octane fuel. But I have also heard that high octane fuel is not necessary and can damage your motor. What do you guys think?

[bullrdr6]

My 2003 225 Opti calls for 87 or higher. I talked to my dealer and he recommended the 87 because it will burn cleaner than higher grades of fuel. I've run 89 and higher occaisionally but all I can tell is that it costs more.

I also use Mercury Quickleen about every other tank.

Charlie

[sparkie_212]

I have never seen an Owners manual that tells you to use 87 octane fuel. Every motorized vehicle I have ever owned has said use a MINIMUM of 87 octane, or whatever the number may be. My vote is for the highest octane. I know for a fact that I get better gas mileage running high verses low and much better performance. I would also have to argue the High oct burns cooler than low. Back in my po boy days when I drove a 78 trans am, I lost the heater core. Didn't have the money to replace it and for some reason was driving around with about a 6"x 8" hole in the fire wall where the old core was mounted. It was winter time and I used the heat off the motor to get by, seaping through the hole. Long story short, when I burnt 92 oct compared to 87 that engine put out more heat burning 92 octane. IMHO, I say high octane burns cleaner hotter and you use less per mile.

[CTFSHWHISKER]

the running attitude in different grades all depends on the timing and compresiion of your engine higher the compression the higher grade fuel you should run,ignition timing can be adjusted a few degrees to allow for low grade fuel.my dad has an 89 150xr4 and it will hardly start on anything less than 89 it runs 125psi compresion my 200 johnson runs fine on 87 but it only has 105 psi it may turn 150 rpm more with 89 or higher.

[kc]

Octane is the rating in which fuel ignites under pressure. The only reason to use high octane fuel is if you have a high-compression (racing) engine that when low octane fuel is used you have pre-ignition or pinging. When an engines pings not only is it not performing well but it can damage the valves.

If you don't have a high compression engine you are throwing your money away paying for high-octane fuel. The best bet is to go with what your owners manual calls for. I have a 135 hp Optimax and it calls for 87 octane just like my Chevy Silverado.

kc

[SSKY]

kc is right. the old feul we had had lead in it. Which contained tetra ethyl lead which is a compound to create a free radical reaction during the burn to slow the combustion process in high compression engines. Now octane is tetra ethyl ether which does the same thing without the lead. The old stories about the lead being in the gas to cushion the valves of four strokes is not true. The higher the octane the slower the gas will burn, which is what you want in a high compression engine. Use what is recommended for your motor by the manual. Higher grades of gas,depending on the source, do have more detergents which will delay varnish and there fore ring wear for the long haul but will not improve the performance of the engine. Also better quality 2 cycle oil have better detergents to prevent carbon build up over the years. I have rebuilt my 84 johnson 75 3 times thus far, and its longest life to date has been while using the manufatures oil and top grade gas. Break down in the winter way up the south fork with no boats around and you will become a beliver.

[kyriver]

Gator, are you confused now==========

[Big John]

I agree with half of what Lawnman said the lower octane does burn hotter but it helps burn the carbon deposits off. That is why high octane fuel has so much detergent added to it.

[dpfishin1]

>What grade fuel do you run
>through your motor? I've
>heard those who run a
>low octane fuel called idiots
>by those who only run
>high octane fuel. But
>I have also heard that
>high octane fuel is not
>necessary and can damage your
>motor. What do you
>guys think?

I HAVE 96 EVINRUDE 200 VINDICATOR. I RUN 87 OCTANE, BUT I ALSO RUN STABILIZER YEAR AROUND. NEVER HAD ANY PROBLEMS.

[LAWNMAN]

low octane fuel ,when it is ignighted has has a slower burn to it so the fire last longer and that makes more heat compared to higher octane that burns faster,so there is less heat, that makes your engine run cooler, that is why they will perform better. i dont know about the cumputers and if they can tell the differences in octane . the carb run engines are better off with high octane. and good oil.and cold plugs. my thoughts... jon hoover

[BillDay]

High octane burns SLOWER than low octane fuel. The reason currnet manufacturers advise the user to go with lower octane fuels is to REDUCE cabon buildup, a by product of combustion. Low octane fuel burns faster and more complete than high octane fuel, therefore there is less carbon build up. The engines today are "mapped" to use the low octane fuel. if you use high octane on a stock engine, you will get carbon buildup which can lead to engine failure after extended use.
Bill Day

[Richman]

My 2 cents....burn what the manufacturer recommends. I run a 10 year old Merc 150 XRI on 87 octane. It runs great and does what I need it to do. Never a problem with it.

Good luck

Rich