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Old 25 July 2019, 01:16   #1
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Yamaha F150 High Fuel Consumption

Does anyone have any suggestions on what to check with my 2008 150 Yammy? Fuel use has gone from averaging 1.0 LPM to 1.5 LPM.
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Old 25 July 2019, 06:58   #2
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Fouling on hull? New anti foul used? Tubes at different pressure? More weight onboard?
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Old 25 July 2019, 08:56   #3
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As above but also Change in driving? Massive difference between sticking under 4000rpm cruising about or pushing along at 5000. Low speeds also. My boat(twin 150 mercs) will use twice the fuel doing 10knts compared to 25knts. Rough water will impact considerably also.
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Old 25 July 2019, 09:04   #4
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Is there possibly water underfloor adding extra weight. I lose a little fuel economy in calm conditions due to water surface drag, were each of the sea conditions you measured the economy from the same.
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Old 26 July 2019, 03:09   #5
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Thanks all for the suggestions and ideas, good food for thought.

There is some fouling, not much and certainly not enough to add 50% to the fuel consumption. But thats my priority in any case.

One tube has a slow leak so it does tend to be softer, what's the physics behind that causing drag? The tube literally sits in the water maybe?

Driving style has not changed much, in any case all my fuel runs are of over an hour at an average speed of 18-23kn which used to the sweet spot. The engine in running rough in the mid range, so I have changed the injectors and ordered a new coil.

Gear box oil also needs doing, would that be a factor? I am told these engines need a twice a season change.
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Old 26 July 2019, 05:42   #6
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>>>>>> The engine in running rough in the mid range, ....<<<<

I'd doubt that was a coincidence...compression check.? smoking ?
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Old 26 July 2019, 13:24   #7
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I'd doubt that was a coincidence...compression check.? smoking ?
No smoke and the engine started playing up after the consumption went up, there is a smell of unburnt fuel which made me think its an ignition issue. Though the injectors definitely needed doing as well, the top was down to 5000 rpm.

Will do a compression check, thank you for that tip.
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Old 26 July 2019, 20:59   #8
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Sounds like an injector. Quite common and easy to replace. I actually carry a spare set onboard
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Old 26 July 2019, 23:07   #9
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Quote:
Originally Posted by Obsidian View Post
Thanks all for the suggestions and ideas, good food for thought.

There is some fouling, not much and certainly not enough to add 50% to the fuel consumption. But thats my priority in any case.

One tube has a slow leak so it does tend to be softer, what's the physics behind that causing drag? The tube literally sits in the water maybe?

Driving style has not changed much, in any case all my fuel runs are of over an hour at an average speed of 18-23kn which used to the sweet spot. The engine in running rough in the mid range, so I have changed the injectors and ordered a new coil.

Gear box oil also needs doing, would that be a factor? I am told these engines need a twice a season change.

The physics behind drag is air reduces drag, so a light chop will increase your performance. My last boat had a slotted hull which created its own steam of air cutting down surface friction, something commonly used in race hulls. This method is also used in slower ships to greatly improve performance and reduce fuel consumption. It doesn't take much fouling of a hull to reduce performance at all. Ships are now using silicon paints as anti fouling as this again greatly increases performance. I would be looking at cleaning the hull and getting the engine inspected if it was mine but starting with the hull scrub ( possibly on a beach an hour before the bottom of the tide.

A choppy surface does this same thing on planing hulls.
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Old 27 July 2019, 05:50   #10
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There is some fouling, not much and certainly not enough to add 50% to the fuel consumption. But thats my priority in any case.
Have you used this boat previously with this degree of fouling? If you can feel the fouling it will have a marked effect. If there are ANY barnacles, no matter how small, it could most certainly knock your fuel use up by 40-50%

A lot of boaters tend to cruise at a particular rev range. You'll see speed fall away at a given rev once fouling begins.
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