High Test or Regular

[Gator]

I'd like some advise please. My outboard is 1984 merc 150, would you reccommend high test or regular. I have (in the past 20 yrs) used high test esclusively but since the price is so high now I've used some regular and it actually "seems" to start better. Could that be my imagination? Would you reccomend high test or regular?


Thanks
emoScratch

 

[blindarrow]

I have a '71 merc 650 (65hp), and I run 100LL aviation gas in it. emoLaugh

 

[beetlespin]

Most likely should use 87 octane. People don't know it but using gas with too high octane causes carbon buildup in the engine. The higher the octane, the slower the fuel burns. If it doesn't burn it turns into that black stuff that gets all over the prop. That same stuff gets in the engine.

 

[Carl Guffey]

I too, am running a older model merc., I am a firm believer in high test fuels. There are several pros and cons to both. My understanding is that higher octane fuels have a higher flash point(biggest difference) so the piston is going higher in the cylinder before ignition of the fuel begins providing a higher combustion effort and cleaner burn. I have seen this in engines torn down, low octane fuels just don't burn as clean in older model engines. You can offset some of this with better oils, such as Amsol or Klotz($40.00 dollars a gallon) but the difference in cost for higher performance oils is at times more than just burning hightest fuel and a less expensive oil. I personally run high test with a performance oil, I turn 6000 to 6200 rpm most of the time and have logged 1800 GPS miles in my boat in the last year. At the 2006 Southern Divisional I logged 600 miles in one week, I was making a round trip of 180 miles per day.( If motors wher'nt meant for WOT then why do the pedals go all the way to the floor?)

You are probably right about the easier starting, a lower flash point will require less effort to turn the motor over, at least for a while.

 

[Bubbakat]

Guys I know this thread is going to start an argument but This is the take on a 2 stroke and high test fuel
The higher the octane the more complete and slower the burn and as was stated can cause carbon build up in a 2 stroke enging while at idle. A 2 stroke does not like that complete burn so any thing above 87 octane is a waste of money./

 

[beetlespin]

Higher octane fuel only helps if your engine has the compression to burn it regardless of whether it is a two or four stroke. If the engine is designed to run 87 octane that's what you should run. I had a hydrotec phase 2 kit on my Yamaha hpdi which included shaved heads and I had to move up to 89 octane. Maybe Paul Nichols with chime in on this one. He knows a lot about those engines.

 

[blindarrow]

I should add too that I do not run 100LL straight in anything I use it in (I use it in my boat, lawnmower, truck, etc). My main reason for running it? I get a good bit of it (20 gallons or so a month) for free, thanks to my workplace.. I also get free Jet-A (aviation kerosene), which I burn in both my kerosene heaters in my workshop area, as well as the tractor (diesel engines will run this if you mix it with regular diesel).

So yea, why pass up free fuel? I heat the shop for free in the winter, and my yardwork is done without having to pay for fuel. Pretty soon I'll be purchasing a diesel truck, which I'll convert to run on used cooking oil, and I'll be driving for practically free too.

In the end, it boils down to the almighty dollar for me.

 

[ditchdoc666]

I have a older 150XR2 Merc and have always run regular in it and I now mix my oil w/gas runs strong and never had a problem with it cant see going higher when using about 50 gallons a week on the lake,my.02 worthemoAngler

 

[inthebox30lbs]

When I fished the great lakes we trolled all of the time. 6 to 8 hrs of trolling a day for years. We ran high test gas and it was an advantage, my dads Johnson idled better and the plugs would not load up as bad as they would with 87. I do recall our mechanic up there telling my dad that he should not be running hightest in that outboard. Running bass rigs were you are rarely idling for extended periods of times I can't see the benifit of paying the extra for high test gas. Put the extra money into stabil or seafoam into your gas.
scott

 

[REDFORD]

Wow I think I will just start using 89 then I will be half right. emoBigsmile

 

[MadBomber]

I bought my 150 evinrude in 95.  The owners manual recommended high octane gas but stated that if I used regular to make sure I used TC-W3 oil.  That's about all the book had to say about it. 

 

[fishinvol]

Paul Nichols recently rebuilt my 89 Mercury and he recomended using 89 octane.

 

[Guest]

What about a four stroke outboard? Does anybody know what is recommended in them. I am about to purchase a 115 Suzuki four stoke engine. I know the manual will tell what grade to use but I'd like to hear what other's experiences have been.

 

[Kingfish]

I don't have a bass boat just a '92 25 hp evinrude. My Owners manual says to use High Test and I always have.

 

[Gator]

Wow !! Quite a response and greatly appreciated. I'm thinking I'll run regular most of the time and put 6 gal. of high octane in every 4 tanks or so or possibly go with some SeaFoam occasionally. Thanks for all the opinions. emoGrouphug

 

[honkytonker26]

They are putting ethenol in 89 octane gas now. I've heard thats bad about carbon build up.

 

[minner]

honkytonker26 - 4/1/2008 12:47 AM

They are putting ethenol in 89 octane gas now. I've heard thats bad about carbon build up.

I'm not trying to start anything but I wanted to add my $.02 to what Honkeytonker said. Ethanol "shouldn't" increase carbon build up in our outboard. Ethanol by chemistry is a solvent, if anything it should reduce the carbon grown in your engine. The problem with Ethanol in association with boats isn't carbon at all. Ethanol bonds with water (I'm sure you've heard this by now, it's the reason they can't pipe the stuff). In most of our boats, our gas tanks sit idle for long periods (a week or more), all gas we buy has a certain amount of water in it and we all experience fuel separation. Ethanol exacerbates the problem to a whole new level because it "likes water" molecules. Ethanol fuel will separate quicker leading to the engine problems we already know about.

The second thing worth mentioning is the solvent properties. Ethanol will actually clean your fuel tanks and fuel lines (think 1970's and 80's when ethanol was popular, a lot of rubber fuel lines got eaten up then). Cleaning your fuel supply system sounds great but you better have a very good fuel filter to catch all the new broken up crud coming through the fuel lines or else it will end up in your carbs, injectors, etc.

Oh, yeah one last thing. Ethanol is much less efficiant in an internal combustion engine. Ethanol burns at lower temperature than pure gasoline with means the overall change in temperature during the engine cycle is less which means poorer fuel economy.

 

[jon the fisherman]

minner has hit the nail on the head.

older motors usually need the high test gas, since quality of fuel is not the same as it used to be. I have an 85 merc 90 hp, and the compression has gone up from the years of carbon buildup, therefore I use high test gas in it. Those older motors were running on leaded fuel when they were produced.

Cheap oil is the #1 cause of carbon buildup

 

[beetlespin]

Minner,

I agree with all of that but the solvent part. Gasoline is also a solvent. High octane gas will cause excessive carbon buildup if your motor doesn't have the compression to burn it. Aside from rebuilt/hopped up motors, promax's, and some merc racing engines 87 is the way to go. Not for the money savings but because it is better for the longevity of the engine!

 

[minner]

beetlespin - 4/1/2008 8:33 AM

Minner,

I agree with all of that but the solvent part. Gasoline is also a solvent. High octane gas will cause excessive carbon buildup if your motor doesn't have the compression to burn it. Aside from rebuilt/hopped up motors, promax's, and some merc racing engines 87 is the way to go. Not for the money savings but because it is better for the longevity of the engine!

Ethanol is a solvent. I don't quite understand what we are disagreeing on, Honkeytonker was talking about ethanol increasing carbon build up which I addressed. You are talking about higher octane ratings increasing build up. I never said anything about octaneemoScratch. I agree though, you have to have the compression to burn high octane. The octane rating is nothing more that a measurement of resistance to autoignition of a fuel. If an engine doesn't have the compression to overcome the resistance then it doesn't get a good burn, which leaves unburned particles in the cylinder (build-up).