Fuel consumption on a Johnson 88 SPL 90 HP

Discussion in 'Outboards' started by cthippo, Dec 27, 2020.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    I agree, if you need to open the throttle to achieve your desired cruise speed, you need a bigger engine. "Excessive operation", aka thrashing, is rarely good practice with any machinery, it shortens the service life.
     
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  2. ondarvr
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    ondarvr Senior Member

    I've owned many of these old crossflows, they were fairly good and simple, nothing that I'm wanting to return to though.

    I'm on many boating forums and you'd be amazed at how many people run outboards at wot almost all the time.

    Being equipped with the lowest possible HP to meet a price point creates the need to run at, or very near wot just to get around.

    I was never able to make myself do it, typically backing down the throttle only reduced your speed marginally.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I guess the price of fuel being lower in the USA than many other places, played a part in that. In any event, in offshore boats, if appropriately powered to plane reasonably easily, WOT is too fast for comfort.
     
  4. ondarvr
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    ondarvr Senior Member

    The most common failure on crossflows was carbon build up from being over propped and lugging.

    Carbon builds up in the ring lands and eventually the top ring breaks and takes the top edge of the piston with it. They frequently still run sort of OK after this happens, just not good.

    The piston ring locating pin can also back out, it eventually goes away and the ring spins and catches a port. The ring breaks and so does the piston edge. I had this happen, it still ran much better than you'd expect.

    This was so common that as soon as someone said their crossflow was running odd they were told to check the compression.

    Making sure it can easily reach or exceed the top end of the RPM range can significantly extend their lifespan.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, I'm not sure what could have prevented some of the carbon-clogged rings, compression drops as well, better quality two-stroke oil was allegedly the best preventative. The V4 OMC had issues with the rubber flow restrictors in the water passages, they perished and motors got hot.
     
  6. Barry
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    Barry Senior Member

    Gallons per hour is a poor focal point
    Several years ago at the Seattle Boat show there was a about a 36 foot aluminum Rib with a cabin and 5 , yes 5, 300 hp outboard engines on the back. I was curious as to how much fuel that the boat held ie range, and he said that it burned about 50 gph. BUT at 55 - 60 mph

    So about 1.2 mpg. Not bad, our 40 on step with 700 hp (twin diesels) would give us about 1.1 nautical mile per USG.

    The focus should be on MPG. If you burn 12 GPH at 24 mph, and are getting 2 MPG, or perhaps you throttle back to less rpm and say burn 10 GPH at 18 MPH and get a poorer MPG rating or 1.8 MPG

    A quick look at Mr E's table shows that you should run at 4000 - 4500 for the highest MPG and hence best efficiency, ie fuel burned for distance travelled, at this rpm
     
    Last edited: Jan 8, 2021
  7. ondarvr
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    ondarvr Senior Member

    Yes, the flow diverters would swell up, change shape and block or restrict the water flow. It was an easy maintenance item.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Hmmm, It sounds like a gross underestimate for 5 of those monsters on the back, and especially at that speed. People should consult websites with actual test data.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, a nuisance that required removal of the cylinder heads.
     
  10. gonzo
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    gonzo Senior Member

    That is a wrong setup to go fast. The extra weight slows the boat down.
     
  11. ondarvr
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    ondarvr Senior Member

    Old crossflows don't compare well with fuel injected 4 strokes, or just 4 strokes in general.

    At wot they use about the same amount of fuel, but 4 stroke efficiency is much better at less than wot RPMs.

    The Crossflow design on these motors is based on 1950 and 60s technology, they did tweak them over the years, but the design was getting old in the 80s.

    I had an early 200hp version too, it ran well, but it didn't put out anywhere near 200.
     
    Last edited: Jan 7, 2021
  12. fallguy
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    fallguy Senior Member

    I have a 2004 50hp four stoke Merc, run it wide open or back a hair a LOT; motor has 2000 hours.

    It'll idle a tad rough now n then.

    Two strokes are so much more subjective, oil mixes, air ratio.

    I have a 65 hp older 2 stroke '64 Merc on a boat and it is terrible on gas. Burned like 15 gallons running around a couple hours at various speeds, light 16' boat and a few passengers
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Of course, I just posted that to illustrate the runaway fuel use at WOT for virtually any engine, with nowhere near a corresponding increase in speed.
     
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  14. Mr Efficiency
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    Mr Efficiency Senior Member

    What revs are you running with the four stroke ?
     

  15. brendan gardam
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    brendan gardam Senior Member

    I went fishing offshore this morning in one of my boats . That one is 17 ft with a 1982 johnson 115 crossflow and I checked the fuel consumption. In ocean swells never over 3/4 throttle it got roughly 1.5 km to the liter. That is my fourth 115 crossflow. But when I had the 85 hp v4 it used a lot less fuel than that on the same size boat.
     
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