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  1. #1

    Stndard or super fuel pros and cons

    I am considering switching to super fuel in my 40hp 2stroke yammy .any suggestions /thoughts welcome

    new horizons

  2. #2

    Re: Stndard or super fuel pros and cons

    High octane fuels are for high compression engine. Use what the manufacturer recommends in the manual. IF the manual does not say to use higher octane fuels, you are better off sticking with regular unleaded as the turnover of the fuel is typically much higher


  3. #3
    Ausfish Addict Chimo's Avatar
    Join Date
    Jun 2006
    Location
    Gold Coast

    Re: Stndard or super fuel pros and cons

    A guy I trust told me a day ago that 98 goes off a lot quicker than 91.

    I know the 91 I use seems to be fine even though sometimes it sits, as a full tank, for months at a time between uses. It always gets filled to the brim after use so very little air in the tank which might also help to minimize water take up from the air..
    What could go wrong.......................

  4. #4

    Re: Stndard or super fuel pros and cons

    My 4.3 Volvo diesels (runs on) on 91 so I use 98. Can be months between outings and it seems fine though I always top it off with 30 litres or so on the way out.

    Sent from my SM-G900I using Tapatalk

  5. #5

    Re: Stndard or super fuel pros and cons

    Quote Originally Posted by TheRealPoMo View Post
    My 4.3 Volvo diesels (runs on) on 91 so I use 98. Can be months between outings and it seems fine though I always top it off with 30 litres or so on the way out.

    Sent from my SM-G900I using Tapatalk
    I would be very reluctant to run diesels on either 91 or 98. I would stick to the recommended cetane rated diesel fuel. Compression ignition engines don't fare too well with petrol (although I think Mazda are working on hybrid spark/compression ignition petrol engines ).

    Cheers



    Sent from my iPhone using Ausfish mobile app

  6. #6

    Re: Stndard or super fuel pros and cons

    I've been told (and heard in a few separate places) that outboards don't require or utilise 98 to its potential. What I have also been told by someone in the industry is that the higher octane fuels keep better. Something to do with the quality controls etc required to manage 98...can't quite remember.

    So I reckon its probably 6 of 1 and half a dozen of the other.

  7. #7
    Ausfish Bronze Member 552Evo's Avatar
    Join Date
    Jul 2016
    Location
    Melbourne

    Re: Stndard or super fuel pros and cons

    I was told the same as RayLamp. When I picked up my new boat with a Merc 150 fourstroke I was told only use regular unleaded (91 octane). That was over a year ago, only done 100 hours on it though. But I will stick with regular. It's what the engines are designed for.


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  8. #8

    Re: Stndard or super fuel pros and cons

    Quote Originally Posted by swof63 View Post
    I would be very reluctant to run diesels on either 91 or 98. I would stick to the recommended cetane rated diesel fuel. Compression ignition engines don't fare too well with petrol (although I think Mazda are working on hybrid spark/compression ignition petrol engines ).

    Cheers



    Sent from my iPhone using Ausfish mobile app
    Sorry poor wording on my part...it's not a diesel engine - "dieseling" in a petrol engine means it runs on after the ignition is off
    Typically when the head and valves are carboned up which isn't the issue here - it just needs the higher octane fuel.

    Sent from my SM-G900I using Tapatalk

  9. #9

    Re: Stndard or super fuel pros and cons

    Quote Originally Posted by NEW HORIZONS View Post
    I am considering switching to super fuel in my 40hp 2stroke yammy .any suggestions /thoughts welcome

    new horizons
    Given that oil reduces the octane rating of fuel - smart move.

    I use BP 98 in everything I have, except for the cruiser which is Caltex 95 on-sold by Baileys Fuels at the dock because I have no other choice. I use Stabil storage in my 2 stroke fuel mixes and Starbrite Startron in the cruisers tanks (nearly 1,000 litres) which has eliminated all traces of water I used to see in my fuel filters when I wasn't using an additive.

  10. #10

    Re: Stndard or super fuel pros and cons

    [QUOTE=juggernaut;1637446]Given that oil reduces the octane rating of fuel - smart move.

    fair comment if he uses pre-mix, oil injection wouldn't be a problem!

  11. #11

    Re: Stndard or super fuel pros and cons

    Quote Originally Posted by TheRealPoMo View Post
    Sorry poor wording on my part...it's not a diesel engine - "dieseling" in a petrol engine means it runs on after the ignition is off
    Typically when the head and valves are carboned up which isn't the issue here - it just needs the higher octane fuel.

    Sent from my SM-G900I using Tapatalk
    Dieseling in low compression engines is usually a problem with high cylinder head temps. Maybe the cooling system needs attention?


  12. #12

    Re: Stndard or super fuel pros and cons

    Quote Originally Posted by TheRealAndy View Post
    Dieseling in low compression engines is usually a problem with high cylinder head temps. Maybe the cooling system needs attention?
    Yep fair point Andy but I checked head temp with an IR sensor and no issues. Timings a possibility too but it runs well and I chucked my timing light years ago. I have read that people in the US have similar problems with low octane fuel on these truck engines.

    Sent from my SM-G900I using Tapatalk

  13. #13

    Re: Stndard or super fuel pros and cons

    Maybe I am just lucky but in 30 years of boating running all sorts of two stroke engines - premix, old school oil injection and for the last 5 years an E-Tec, I have never experienced any sort of fuel issue running standard grade fuels - even with periods of lay up of 6 months without running any sort of additive. I don't bother topping off tanks after a day out - I refuel the day I am going but sometimes that isn't a lot of fresh fuel going in and at times engines are run on year old fuel on the hose at home. I can see the possible benefits with modern 4 strokes with variable valve timing though.
    "I soak the worms in rum. The fish love em and the worms die happy"
    "Alcohol is not the solution to your problems...................but then again, neither is milk"

  14. #14

    Re: Stndard or super fuel pros and cons

    Curious as to how one would actually measure the difference between the fuels whilst on operation?
    You can not go by miles per gallon as the weather significantly changes trip to trip.
    You can not go by horsepower produced unless you can attach a dyno to it somehow.
    You can not go by feel because that is not a guage with a benchmark.

    You are simply asking for other peoples opinions whether their advice is right or wrong.

    I suppose you could borescope the cylinder for cleanliness after running for a suitable distance on one fuel then check again after a similar distance on the other fuel and try to guage any differences.

    FWIW i run regular unleaded on my old two banger and it has run well all of it's 22 years and maybe 5000 plus hours, again the hours there are subjective.
    Jack.

  15. #15

    Re: Stndard or super fuel pros and cons

    Dunno about boats but 20 years or so of extensive testing on all sorts of bikes reveals an increased range of about 10% using 98. I still get arguments but am convinced. An extra 20km to a tank is noticeable when you have to fuel up every 200km or so.

    Sent from my SM-G900I using Tapatalk

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