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Author Topic:   87 octane or premium?
JBCornwell posted 10-04-2002 05:04 PM ET (US)   Profile for JBCornwell   Send Email to JBCornwell  
ChrisB tagged this question onto a different thread. He had been told to use only 87 or 89 octane.

Almost all (All that I know of) manufacturers suggest "at least" 87 octane gas. None ask you to avoid premium.

Many wrenches believe that premium fuel additives increase deposits and make the engine harder to start, as well as other negative effects.

The OMC Manual for my little Johnny 4 stroke 9.9 specifically recommends premium fuel after saying 87 octane minimum. I haven't seen that recommendation in a 2 stroke manual.

My opinion is that the only measurable effect of using premium fuel in a 2 stroke outboard is a lighter wallet.

Red sky at night. . .

kglinz posted 10-04-2002 06:07 PM ET (US)     Profile for kglinz  Send Email to kglinz     
My Merc Opti manuals say 87. Most Marinas in the Pacific NW sell 89. Canada? how knows.
Clark Roberts posted 10-04-2002 06:27 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
So long as an engines compression ratio (and timing) remain in range of design spec. then the minimum grade recommendation will give all the performance capable! Now if an engine gets carboned up to extent that compression ratio goes on the rise then higher octain fuel will delay detonation and detonation damage. The higher the octain the slower the burn/cooler the burn/safer the burn but as long as you keep your engine (2 or 4 stroke) in good condition and tune then seems to me that higher octain is a waste of money... and as mentioned above may contribute to deposite build up... Hey, I remember Blue Sunnoco and the dial your own octain pumps...and those 11:1 Hemi's ... telling my age now! happy Whalin'... Clark.. SCN
Capt_Tidy posted 10-04-2002 07:21 PM ET (US)     Profile for Capt_Tidy  Send Email to Capt_Tidy     
After years of dealing with service stations and doing tank audits etc... I don't think there is such a thing as a pure gasoline grade anymore. There is a lot of mixing - at the refinery, in the trucks, and at the pumps. 87 octane will always be 87... but 89 or higher... who knows... maybe.

If your really want to be sure your using a high grade... use a boost additive.

jimh posted 10-04-2002 09:14 PM ET (US)     Profile for jimh  Send Email to jimh     
I live about a mile from the famous Woodward Avenue, the street racing capital of the midwest in the 1950's and 1960's. A gas station on Woodward sells ultra-high octane racing fuel. I think it sells for about $4/gallon! My neighbors restored Plymouth Hemi runs on the stuff.

I have always wondered what my outboard would do with a tankful, but at those prices I don't think I will be filling up too soon.

11 footer posted 10-04-2002 11:05 PM ET (US)     Profile for 11 footer  Send Email to 11 footer     
I have seen with my 15hp merc runs hoter with higher octane. I do not know it it is good or bad.


Clark Roberts posted 10-05-2002 08:05 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
In my opinion, it is best practice to follow manufacturers recommendations re: fuel and oil and to depart is to risk some sort of damage (like holed and or scored pistons etc). Changing from 87 to 89 or 93 octain is not a giant step but racing fuel may be! Super high octain requires changes in engine timing, spark plug heat range and gap setting if air gap type. I'm no expert, mind you, but have seen lots of baskets of engine parts...hope none are ever mine (or yours)!!!! Happy Whalin'... Clark.. SCN
chrisb posted 10-06-2002 08:11 PM ET (US)     Profile for chrisb  Send Email to chrisb     
Thanks for pulling this topic out. I should have done that in the first place. We always used the cheep stuff, but when someone tells you like its gospel you wonder. Once again I'm indebted to you all.
David Ratusnik posted 10-06-2002 09:35 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
ChrisB- 2 stroke (especially carb 2 stroke) equals 87 ocatane........ it's a no brainer- save $$$'s and put them into some other aspect of your boat. .03 David
BQUICK posted 10-07-2002 10:31 AM ET (US)     Profile for BQUICK  Send Email to BQUICK     
My 1980 90 Merc manual recommends premium.
My 1970 recommended premium "white gas" (Amoco) remember that?

Why take any chances with detonation/preignition?
Plus as gas ages the octane goes away.....certainly something to consider with boating's intermittant use.

Sure they can run on 87 but why take a chance. The exception to this would be if there was no full throttle use (esp extended full throttle).

Most new cars will make more power and get better mileage with premium due to knock sensor and variable timing...


Bigshot posted 10-07-2002 10:38 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Years ago I read where OMC had come into a lake community and did a survey. On one side of the lake they had like 3 times as many engine failures as the other. Most were due to carbon buildup and later ring failure. They concluded that the area with the failures had a marina that only sold 87 octane. The other side of the lake with little or no failures sold 89. The 87 did not burn clean enough in a 2 stroke and carbon built up.

Now things have changed since then(late 80's) and the main thing is that 89 had carbon guard and other additives in it like 93 does. Since then 87 has gained the same additives so that should not be an issue. I run usually 93 in mine just from habit and the fact I have never had any carbon issues(also use OEM oils) and old habits die hard. I do however run 89, especially when tank is empty and I want to save 10 cents a gallon. Maybe it's because I worked in a gas staion in High school and college, I can not run 87....even in my lawnmower. Although I know if it don't knock, 87 is enough, I have to run at least 89.

lhg posted 10-07-2002 05:56 PM ET (US)     Profile for lhg    
The manuals for both my 1985 pre-mix Mercs and my 1997 EFI Mercs recommend 87 Octane. Mechanics at two different dealerships have said 87 is all that should be run on a regular basis. Sometimes a marina will only have 89 or even only 91, and once in a while that is OK, but not continuously. They have told me it causes a hotter combustion and can damage the engine.

Before the advent of TCW-3, there was mechanic talk that the low grade 87's were causing carbon build-up. But now all that is changed with the addition of the de-carbonizing agent in the oil.

Bigshot posted 10-07-2002 07:17 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
And putting it in the gas as well. I still say 89 due to octane dropping over a few weeks/month.
flyguy posted 10-07-2002 08:02 PM ET (US)     Profile for flyguy  Send Email to flyguy     
I got the opinions of 2 mechanics (one in NY and one in DE) and they both said to stay away from high test because of the added alcohol. The alcohol burns hotter; synthetically making the engine run leaner which we know for 2 strokes is very bad. Both said to use 87, 89 being a little better. Both also said that when gas sits in the tanks for weeks on end (if you do that) the octane actually lowers and the gas degrades...hence gas stabilizers. Keep in mind the added alcohol is a regional thing. Just my .02
Jiles posted 10-07-2002 08:06 PM ET (US)     Profile for Jiles    
High-test gas can be bad for your motor! High octaine implies that more energy is available but it actually produces no more then regular. Higher octaine in fuel raises it's burning temperature and requires higher compression pressure to burn effeciently. Using higher octaine in a normal engine results in incomplete combustion,less power, carbon fouling of the cylinder and, most important, wasted money. Gas companies make more profit from high test gas. That is one reason you don't see ads for regular gas.
alan posted 10-08-2002 05:04 PM ET (US)     Profile for alan  Send Email to alan     
2 cylcles were made to burn 87 octane - period. I've done all the research and reading, anything more can cause damage, low combustion rate = carbon buildup.
bsmotril posted 10-09-2002 09:25 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
With respect to Mercs, there was a factory tech bulletin that addressed this topic in the 99-2000 timeframe. It was directed towards the Optimax Motors. My dealer showed it to me back then, but I don't remember the specifics other than use the lower octanes. Your dealer probably has it on file.
Bigshot posted 10-09-2002 09:56 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Most engines are designed to run on low octane....does not mean it runs better. The older an engine gets the more ocatne it requires from what I understand. My CJ-7 would not even think about running on anything but 92+. I tried everything(plugs, timing, etc) and she would just knock. To each his own but I am sticking with 89.
John W posted 10-14-2002 10:21 AM ET (US)     Profile for John W  Send Email to John W     
Probably more important than the octane is making sure to use a major label brand (Chevron, Amoco, etc.) that includes the additive packages to eliminate carbon build up. I think using at least 89 makes sense due to the octane dropping as the gas degrades over time, this may not be necessary if you use your boat all the time & go through a tank quickly.

It may be a waste of money to buy premium, but I don't believe it'll hurt anything, at least on old-tech two stroke father has used nothing but premium in the dozen or so outboards he's owned since the 1960's and has never had a motor failure. His 1983 Merc still runs perfect on nothing but premium; my 1989 Yamaha runs great on a diet of premium or 89 octane as well.

John Bocskay posted 10-24-2002 09:40 PM ET (US)     Profile for John Bocskay  Send Email to John Bocskay     
All the marina's that I've been to on the intercoastal waterway in Florida pump 89 octane but I can't say that some of them might pump 87.. When I had my Yamaha's the dealer said that 87 octane was just fine and not to waste money on any higher octane, I tried switching octane's on 87 and 89 but couldn't tell any difference in milege or performance.
I think Capt Tidy is right on when he talks about octane mixing also.
whalerron posted 10-26-2002 11:59 PM ET (US)     Profile for whalerron  Send Email to whalerron     
"2 cylcles were made to burn 87 octane - period"


Bigshot I agree with you. But, more importantly, I agree with Johnson Outboards. One important point here is that Johnson goes out of their way to state that 87 is the MINIMUM octane to be used in their outboards. The following is directly from the owner's manual for my 2001 90 hp Johnson 2 stroke outboard:

"Your outboard is certified to operate on unleaded automotive gasoline with an octane rating equal to or higher than that specified in Minimum Octane chart."

From the "Minimum octane" chart:
87 (R+M)/2 AKI

Hendrickson posted 10-27-2002 03:10 AM ET (US)     Profile for Hendrickson  Send Email to Hendrickson     
The local (by the lake) convenience store uses 89 octane in their pre-mix. When I asked an outboard mechanic why they did this he stated that the presence of oil in the gas lowers the octane to 87?
JCL posted 10-27-2002 09:30 AM ET (US)     Profile for JCL  Send Email to JCL     
Interesting comments. After 32 years in the
Automotive industry and a long time drag racer I will offer an opinion.
In the 1980's GM issued a tech bulletin that only Chevron and Mobile gas should be used to combat fuel injection clogging. Reason? Additives. Now all the major brands have some form of cleaning additives. Stick to major brands that advertise cleaning additives. Techron in Chevron is particularly good and the higher the octane the higher the concentration of that additive in their product. The downside is that in some states alcohol may be a higher % in the higher octanes. In Arizona Chevron does not use alcohol in higher octanes. I agree Alcohol is not desirable.
The new Mercury TC3 2 cycle plus oil has additonal cleaners,additives to prevent wear in the biggest racing motors and octane boosters according to a Merc Racing tech I know.
Octane recommendations are usually the minimum for most motors..
Personally, in my vehicles I use 87 Chevron but once a month will run 91 in one tank to take advantage of additional techron. The cleaner you can keep the injection system the better.
Outboards, I use the Merc 2 cycle plus oil and Chevron 89 octane. However if the gas available in your area contains increased amounts of alcohol I would stick to 87.
My 1979 Merc 90 was run with Chevron minumum 89 octane gas and Merc oil for 20 years and had nothing but routine maintenance. No failures. At trade in time dealer reported only 6% cylinder leakdown and less than 3 lbs cylinder compression variation. dyno test was in range of new factory specs. (should have kept it)
87 octane should be adequate for motors up to 8>1 compression. The new Yamaha 90 2 strokes only run 6 to 1 or less. Most newer motors have low enough compression requirements to be be used in other countries where octane may be questionable.
You can call the gasoline distributor in your area and ask for detailed info on alcohol or ethanol % in each grade. Be sure you are talking to someone knowledgeable.
For what it's worth.

JCL posted 10-27-2002 10:18 AM ET (US)     Profile for JCL  Send Email to JCL     
To clarify, alcohol and ethanol blended fuels are no problem in cars and trucks because they are designed for it and the fuel is cycled often.
In marine use, when boats sit for longer periods of time, alcohol blended gas can cause degradation of fuel.
BQUICK posted 10-28-2002 09:49 AM ET (US)     Profile for BQUICK  Send Email to BQUICK     
Good point about the oil lowering the octane.
I use a little extra oil so I like the 93.
Worked for 32 years on my 50 Merc.....

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