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Author Topic:   Minimum Octane Rating For Outboards And Their Performance?
whalernut posted 03-31-2001 08:06 AM ET (US)   Profile for whalernut   Send Email to whalernut  
I own a 1975 85h.p. Johnson and was wondering what is the minimum gas octane rating for this engine, as I don`t have the manual? Also, I noticed that the newer outboard motors say they can run on a minimum octane of 87. They also say regular marine and car gas is fine? I was wondering if car gas would be fine for my old outboard and which octane rating? The marina where I purchase my gas has 89 octane. I remember a time when marine fuel was different than car fuel, although I couldn`t tell the difference, it was just publicised as different? I am wondering if the marinas are still using actual marine fuel? Would a premium fuel make my old outboard idle better? And do I need lead in my gas to lubricate it? Any and all comments on this subject would be very much appreciated! Regards-Jack Graner.
Dick posted 03-31-2001 10:33 AM ET (US)     Profile for Dick  Send Email to Dick     
Plain old regular unleaded is all you need. The oil you mix with it takes care of the lubrication.
As I remember from my days of purchasing fuel for the marina fuel was fuel and available in various octain ratings. It made no difference if it were being delivered to a marina or a gas station. Back then we pumped Chevron regular and pre-mix.
whalernut posted 03-31-2001 12:08 PM ET (US)     Profile for whalernut  Send Email to whalernut     
Thanks Dick! Regards-Jack Graner.
lhg posted 03-31-2001 03:57 PM ET (US)     Profile for lhg    
I agree with Dick, and note that the engine manufacturers are all recommending nothing BUT 87 octane. Before TCW-3, some cheap grades of 87 were causing carbon problems, but the newer oils have eliminated that issue. Now, I'm hearing that the higher octanes, like 91 or 93, cause the engines to run too hot and can damage them, especially since the higher octane is acheive by adding more alcohol, which burns hot.
whalernut posted 03-31-2001 07:13 PM ET (US)     Profile for whalernut  Send Email to whalernut     
Thanks Larry-Jack Graner.
B Bear posted 03-31-2001 11:57 PM ET (US)     Profile for B Bear  Send Email to B Bear     
Having once owned a OMC 115 two stroke. I had recieved the following information from the service department at OMC and a certified OMC dealer and repair facillity:

Concuring with lhg about cheap gas and Dick as to the varity of octanes made avalible in the past. The gas used today burns cleaner than the gas in the past no longer needing a higher octane for cleaner burning so 87 octane is fine where as before you would use a higher octane like 89 or 92.

Even with the new TWC-3 oils it is still recommend that you use OMC Engine Tuner about every 20 hours of engine use or add OMC Carbon Guard to your fuel with a VRO tank or to your fuel/oil mix to prevent and reduce carbon build up.

I can't tell you if they just wanted to sell more product, it is just what they recommended.

whalernut posted 04-01-2001 01:49 AM ET (US)     Profile for whalernut  Send Email to whalernut     
Thanks Bear! I have never used the Carbon Gaurd in my fuel, but it seems to be a popular thing on the site here? I usually use Power Tune(SPRAY) in the beginning of the year and that is it, but it seems as though a little here and there(in the fuel) would be better than all at once and then not for a year again? Regards-Jack Graner.
Clark Roberts posted 04-01-2001 11:50 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Octane rating indicates the speed with which the combustion takes place. The higher the octane rating the more slowly it burns and conversely, the lower the octane the more quickly it burns! So the low octane burns with a bang (this is want causes the "ping in auto engines when timing gets ahead of octain rating), and the high octane gas burns more slowly with a whoosh! The slower the burn the more even the pressure on the piston and the less of a "hot spot" on the piston. Also the timing can be set with more advance as octane is increased. If an engine is not in proper tune (proper timing etc) and/or if not operating in correct rpm range at WOT (not enough rpm) the higher octain will be more forgiving as far as engine damage is concerned. If engine is in proper tune and is set-up with correct propeller then the 87 octane fuels are perfect! Interesting to note that the Merc Optimax's engine control unit (ecu - read computer) continuously adjust timing of engine to correspond to fuel octain (also adjusts for temp, rpm etc) but 87 is the recommended octain! Clean fuel, free from water, contamination, alcohol, dirt etc... is what I want! Pass the carb cleaner! Happy Whalin' Clark .. The Old Man and the Sea
NWflyfisher posted 04-01-2001 08:26 PM ET (US)     Profile for NWflyfisher    
I'm now officially confused!

First, please allow me to introduce myself. My name is Greg and I'm the new owner of a 1978 Montauk with a 1978 Mercury 70hp and a I-don't-know-what-year-but-I-think-its-an-80-something Mercury 15hp kicker (will be having the serial number checked this week to find what year.) I've been silently monitoring this board's discussions since my wife and I first began considering a boat purchase back in January. I've always wanted a center console Whaler since my youthful scuba diving days and finally made my purchase two weeks ago. I plan to use it primarily for fly fishing in the Puget Sound region and secondarily in trolling for Kings (Chinook) and Silvers (Coho.) The wealth of knowledge I've gleened from those of you knowlegeable, experienced and willing to share thus far has proven invaluable to one such as me. I've done my homework and reviewed everything available on this site and continually go back and re-review. Dick has been generous enough to share some of his knowlede through exchange of several emails with me which has been exceptionally helpful; I'm grateful for his willingness to share. I bow before greatness; thank you all.

Now, to the crux of the matter. Being a newbie not only to whalers, but to boating in general, I dragged my "new" rig on down to the local Mercury experts in my area (Lighthouse Marine in Gig Harbor, WA.) I was advised to (1)stay away from the "cheapie" gas as found at the local convenience store and only use a "name brand" gas such as Chevron, Texaco etc.;(2) use 89 octane only; (3)use only Mercury Premium Plus 2-Cycle Outboard Oil for the 50:1 mixture and (4) always add OMC 2+4 Fuel Conditioner in the appropriate proportions to the fuel tank whenever adding gasoline.

The various recommendations for using 87 ocatane now have me baffled. I respect the advice I received from Mike (one of the co-owners of Lighthouse Marine) and will more-than-likely follow it to a "T", but all the board's recommendations for using 87 octane now has me baffled.

Anyone willing to take a stab at un-confusing this issue for me?

Thanks in advance.

Dick posted 04-01-2001 09:17 PM ET (US)     Profile for Dick  Send Email to Dick     
The guys at Lighthouse won't steer you wrong.
I don't remember what octane regular gas was back in the 70s but it was higher than 87. There is no way that running 89 could cause any harm, it should also be just fine with the 87. I agree use a quality fuel Chevron, Texaco or Union 76.
You are doing the right thing in running a high quality oil, more important than the fuel, and a shot of 2+4 or a similar product is a good idea.
Clark Roberts posted 04-01-2001 09:19 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Flyfisher, info and opinions herein are intended to give you information from which to make your own decision. The 87 octane recommendation from me is because that's the engine manufacturer's recommended octane! If you feel more comfortable with "Lighthouse" recommendations, along with 89 octane, then you should probably follow those recommendations! Also 89 octane won't hurt your engine. Again, sorry for adding to the confusion.. Happy Whalin'... Clark... The Old Man and the Sea
B Bear posted 04-01-2001 10:09 PM ET (US)     Profile for B Bear  Send Email to B Bear     
Don't be confused. They are recommending those name brands becuase those brands normally are detergernt gasolines that are very clean (less contaniments). So there is no need to use anything higher than 87 octane if your engine timing is correct (the octane number denotes the ignition quality of the fuel as Clark Roberts pointed out, the higher the number the better the quality, less tendency to knock). Although higher octanes may be used during colder weather or higher altitudes. The 2-S TWC-3 provides lubrication and also burns with the gas. The OMC 2+4 conditions the gas and acts like their Carbon Guard product to reduce carbon build up from the burn and exhaust stroke. Since TWC-3 is heavier than the gas it will produce a carbon residue which will kill your power head in time if allowed to build up, which is greater at lower RPMs. OMC Engine tuner is used at the begining of the season to help clear out the fogging oil used for storage and at the recommended 20 hour intervals, as I mentioned to Jack, instead of using OMC Engine Tuner as a maintenace item during the season the Carbon Guard or the 4+2 can be used with the fuel supply.

Now that I have gone to a 4-s I still condition my gas, 87 octane, with fuel stablizer since the new gas will drop in octane over time (even a few months).

NWflyfisher posted 04-02-2001 04:10 AM ET (US)     Profile for NWflyfisher    
Thanks for helping me through my panic attack, guys. :) Sorry to have disrupted the flow of the thread.
blackdog posted 04-02-2001 09:50 AM ET (US)     Profile for blackdog  Send Email to blackdog     
Anyone have experience with the Ficht Injection oil & carbon build up? I havenít pulled the plugs yet to inspect but the literature says it has prevents carbon build up. Should I also use the OMC 4 + 2 with each tank of gas?

As far as Octane the only thing I can add is from my experience with a PWC (I know I hate them now). I owned a Sea-Doo that I had bought used. It ran great for a season then I started to use high-test 93 octanes towards the end of the second season and it died. The performance was noticeably faster with the high-test. The mechanic we used claimed that the high-test had killed the engine. It actually burned a hole on the top of the piston. He claimed they only use regular, and when available the 86 Octane that Sunoco to sells, for their rentals. Not sure how good that advise was but I only used regular from then on and when I filled the Dauntless up this weekend I used Texaco 87 octane.


lhg posted 04-02-2001 03:01 PM ET (US)     Profile for lhg    
Blackdog: If your Ficht is a '99 or '98, carbon build up is the killer, literally, of these engines. I think they solved this major problem on the 2000/01 models with new head design.

To eliminate carbon build up in any 2 stroke, use the tcw-3 (that's what the "3" means, a de-carbonizing agent is in the oil) and a de-carbonizing agent in the gas. My Mercury Mechanic says the Mercury "QuickClean" agent (about $8/70 gallons of gas), added per recommendations on bottle, will keep your engine like new. They swear by this product, and these are guys that pull a lot of v-6 cylinder heads. They told me to use it about every 4th tank of gas, but NOT every tank. Yamaha makes a similiar product. Don't know what's going on with the old OMC products, or whether they have an equivalent. Assume Bombardier will re-label these when they get their act together. But with a Ficht, I would DEFINITELY use the product.

Lil Whaler Lover posted 04-03-2001 12:05 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     
Just a couple of additional observations about the octane ratings for our beloved outboard motors. Here in Central New York, Syracuse area, 89 octane is the only gas available to the local marinas. I think it is this way for for a couple of reasons. First, there are many high performance boats in the area, and these require at least 89 octane. For the most sophisticated rigs, one marina sold 110 octane racing fuel at about $3.50 per gallon last summer. Secondly, it is difficult to get EPA (or whoever) approvals for gas pumps at lakeside so a marina usually limits itself to one storage system and makes it 89 octane as a compromise to satisfy as many people as possible. They will lose customers if they only offer 87 and will be undersold if they try to sell 93.

As others have said, it may be more important to use good oil than to fret over octane. Our engines are very forgiving on octane requirements.

Not to extend this any further, but does anyone out there remember when marine white gas was marketed? I remember it in the 60's. It was done to get the lead out so the engines would run better. Ironically, when lead was finally dropped from gas, many high performance 2-strokes suffered a drop in performance without the lead. Of course the gas quality was pretty poor at that time. Seems like history goes around in circles a little too often.

blackdog posted 04-03-2001 09:06 AM ET (US)     Profile for blackdog  Send Email to blackdog     
Thanks Ihg, I have the 2001 model thankfully. I have heard they solved all the past problems with the 2001 model year. I spoke to the new service manager at my dealership. He recommended the use of OMC 4 + 2 . It sounded like it couldnít hurt type of suggestion; I donít think he really had an idea.


bigz posted 04-03-2001 09:57 AM ET (US)     Profile for bigz    
Lead was used as a lubricant, and Amoco was one of the few refiners who marketed white gas back in the 50's thru the 70's promoting the fact that it was pure clean lead-less gas -- cleaner burning, high octane, no knocks etc. etc. (after gas moved to all non leaded wasn't a biggie selling point for them) --- as far as marine use don't recall Dave --- but I do remember having to have your outboard upgraded in the mid 80's to use non-leaded gas by your manufacture's dealer. This was due if I recall to the alcohol additive in non leaded!

Oh another thing, aside from octane as described by Clark Roberts, the difference in brands (if any) depends on the additive package developed by that brand (interesting to note that the "discount" stations maybe severing up any of the major branded gasoline on any given day) -- One major problem is right at the pump which is often overlooked -- doesn't make a hoot of difference reg. super reg. hi test --- if the gas was not filtered properly out of the stations storage tank --- (another area where this can compound the problem is when the refinery loads it into tanker trucks, if the huge storage tank is near empty -- you can bet your bottom dollar that load is going to have a high percent of water in it)! Don't care which brand you purchase all come from the same refiners within an area --- and the additive packages are added per brand specification, again it is at the pump where the problems can occur if the station doesn't maintain their filter systems -- including marinas

That said --- just another sound reason you should have a quality fuel filter installed on your boat even a 13!

PS a little trivia

For years Gulf didn't have the close tolerance cracking ability to control each grades octane levels precisely--- their regular octane for the most part (since you had by regulation be exact or exceed the octane rating) was a great buy for the customer since it would be equivalent to today's super reg or whatever it's called about 88 to 89 octane rating ---

dgp posted 04-03-2001 12:43 PM ET (US)     Profile for dgp  Send Email to dgp     
Tom, you're not gonna start that fuel / water seperator thing again, are 'ya? Hey, what size cement shoes do 'ya wear? Don
bigz posted 04-03-2001 01:09 PM ET (US)     Profile for bigz    
Thought never crossed my mind ;)!

Why a pair of 27's at present :)!

whalerron posted 04-11-2001 11:25 PM ET (US)     Profile for whalerron  Send Email to whalerron     
whalernut - I own a 1975 70hp Johnson and page 19 of the Owners Manual, which I am holding in my hand, recommends that a good quality fuel with a minimum octane of 89 should be used.

I would assume that our motors have the same fuel requirements but I don't know that for sure.

- ron

whalernut posted 04-12-2001 08:48 PM ET (US)     Profile for whalernut  Send Email to whalernut     
Ron, thanks for the info. I am also curious as if my engine requires the same octane as you`res? Any one know if it does? Regards-Jack Graner.
Chesapeake posted 04-12-2001 10:28 PM ET (US)     Profile for Chesapeake  Send Email to Chesapeake     
You gents know the science and specifications of ingine burns far greater than I. That said, the motor I am replacing is a '75 Johnson 85 HP. I have always depended on my 70 year old motor guy who only works on OMC stuff. About 3 years ago, I was still mixing lead additive in with my oil and gas. He pulled out a sheet / flyer from OMC that basically said you could stop using lead additive / leaded gasoline on the '75 model year motors provided that a "premium unleaded" gasoline is used. Now maybe that has been changed by OMC -- I don't know.

The worst of it is that my old timer motor guy in Madison, WI just won't work on a Yamaha. Now THAT is the worst thing about my repowering. I guess it's time for another project boat so that I can buy my old Johnson 85 HP back.

Hope the spring is being kind to you all.

Bob (Chesapeake)

carlz posted 04-14-2001 10:30 PM ET (US)     Profile for carlz  Send Email to carlz     
The suggestion that higher octane gas can cause burnout sounds a bit apocrypal. I'm no engineer, but I suspect that as you cannot be too thin or too rich your octane can be too high. As commented earlier, knock is caused by the too-quick explosion of lower octanes; but how can the slower burn of higher ocatanes cause a problem? You may simply not be getting the advantage of the higher octane from your gas. Like cars, there cannot be a one size fits all rule on octane and the mfg.'s recommendation should be the starting point.
One of the diferentiators of the various grades of gas--even within a brand-- is the amount of detergents. This is where the higher octane gases may provided an atvantage, by fighting the great killer of 2-cycles, carbon buildup. That's what my mechanic told me, anyway. I buy the good stuff when I can.

carlz posted 04-14-2001 10:31 PM ET (US)     Profile for carlz  Send Email to carlz     
that should read " your octane cannot be too high"

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