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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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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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Old 27 July 2019, 09:35   #11
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The physics behind drag is air reduces drag
Thanks Jon, how does matching the pressure in RIB tubes have this effect though?
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Old 27 July 2019, 09:37   #12
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If there are ANY barnacles, no matter how small, it could most certainly knock your fuel use up by 40-50%
I am sure there are some and they will be growing all the while!

Still need to sort the misfires out, but pressure wash and fresh AF are now the top priority - thanks Will!
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Old 28 July 2019, 09:12   #13
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Thanks Jon, how does matching the pressure in RIB tubes have this effect though?
Sorry, I wasn't referring to different pressure in tubes, I was referring to different sea conditions between testing, as chop reduces surface tension ( air under hull ). When I head offshore in the mornings my speed is 32-35kh at 4500rpm travelling 2.4km per litre on glassy flat water. Once the wind picks up, my speed picks up to 40-42kh and 3.2 km per litre at the same rpm 4500. This is from a clean hull kept on a trailer. By the way I'm referring to my Yamaha f 70.
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Old 31 July 2019, 10:28   #14
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If you can feel the fouling it will have a marked effect.
Gave her a scrub off today, one hull had definite growth on the outside. The other was clean (dark side of the pontoon) and the centre void was not too bad.

Will hopefully get a decent run on Friday and Saturday to see what its like, new coil arrives then as well.
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Old 01 August 2019, 10:52   #15
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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.
Injectors needs to spray fuel not squirt fuel. When fouled, the latter increases the fuel comsumption, will need to ultrasonic clean the injectors or change them which could be costly...

Happy Boating
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Old 01 August 2019, 13:05   #16
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Thanks for the suggestions about injectors but from my post of the 26th...

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The engine in running rough in the mid range, so I have changed the injectors...
Playing around with the ignition coils tomorrow!
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Old 19 August 2019, 05:19   #17
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Update....

Found one culprit - the depth transducer is a large (Garmin CHIRP) transom mounted one and it was quite heavily fouled including some barnacles. That must have been causing a fair bit of drag.

Not tested the economy yet, as the engine is still running rough. Things I have done so far....

Changed the injectors, plugs and oils.
Swapped out the coils with a new one.
Cleaned out or replaced the fuel filters.

None of that has made any difference. Still ticks over badly and runs rough until over 3200 RPM.

Waiting for the local (ish) main dealer to have time to have a look, so any other suggestions would be much appreciated. Not done a compression test yet.
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Old 20 August 2019, 01:20   #18
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I had a similarish issue that turned out to be the crank shaft sensor. Despite being categorically told they either work or donít I only found out the issue when it died for good. Itís a cheap enough part fortunately. My mercury suffered lack of power and ran a little rough but performed better at high end.
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Old 20 August 2019, 02:18   #19
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... turned out to be the crank shaft sensor
Thanks

I shall look into that option.

Did a short run yesterday, 12nm and used 18 litres. So its still 1.5:1

The hull is clean - so it must be the engine under performing.
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Old 20 August 2019, 02:25   #20
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Thanks



I shall look into that option.



Did a short run yesterday, 12nm and used 18 litres. So its still 1.5:1



The hull is clean - so it must be the engine under performing.
Yamaha one was same as my merc one. If you could borrow one for an hour of a mates engine
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