Fuel economy on 15 HP Merc four stroke,...what to expect?

[SeaNymph Man]

I am still waiting delivery on my new 2010 Lund A-14 utility-v bottom boat that will have a 15 HP Mercury four stroke outboard for power as the A-14
is rated for 15 HP max. Compared to my old 18 HP Evinrude Fastwin 18 on my
current boat which is being traded for the Lund,what kind of fuel economy should I expect out of the Merc four stroke say at speeds of half to three quarter throttle most of the time with short full throttle runs occasionally?
One other question would be that after reading the engine FAQ board about four strokes 'making oil',since I do not keep my boat in water when not in use,
will I experience the problem less than others who keep their boats in water
during summer months when not in use? This is going to be my very first four stroke motor,so I just wanted to know some things ahead of time.

 

[steelespike]

Re: Fuel economy on 15 HP Merc four stroke,...what to expect?

It is next to impossible to guess partial throttle fuel use.
A 15 will use "about 1.5 gph(gallons per hour) @ wot(wide open throttle).
Of course less at partial throttle.
The little 4 strokes require very careful setup and prop selection for ideal performance.We can help you fine tune your setup.I would be very interested to see how the 15 compares to your old setup.
To get the best setup you may need a tinytach and a gps for speed.
an 18 is good for about 27 mph on a light reasonably fast boat.
A modern day 15 probably 25-27. on the same boat.

 

[TOHATSU GURU]

Re: Fuel economy on 15 HP Merc four stroke,...what to expect?

15C (4-str)
5,500 RPM
1.3 gallons per hour

 

[Silvertip]

Re: Fuel economy on 15 HP Merc four stroke,...what to expect?

I normally use the Yamaha web site for "rough" fuel consumption information since they have a very nice collection of performance tests for nearly any boat on the planet (or at least you can find one very like the one you are interested in) as well as fuel consumption, time to plane and rpm at given speeds. They do not list a 15 HP on a 14 foot boat but they do show a 20 HP. Even the 20 HP charts don't show fuel economy numbers because the consumption rate is too low for the test equipment they use. That is reasonable since most fuel flow monitors are of the turbine variety and require a certain flow rate to provide any reasonable accuracy. The only other way to do it is to monitor speed and rpm accuractely and simply run a given distance for a given at a given rpm and then measure the amount of fuel used. Way too tiime consuming for the number of boats and engine combinations available. Besides -- you own a boat. If you have to worry about fuel consumption it was not a wise investment. Your new boat will burn less fuel than the old one. The amount different will not amount to enough that a bulge develops in your wallet from fuel savings. As for the "making oil issue" that has nothing to do with the engine being on the water or in the garage. Making oil results from not getting the engine up in the rpm band often enough. Oil gets diluted with fuel from the very slow operating speeds caused by trolling for extended periods. To prevent or at least minimize this issue open the thing up now and then. Poking along constantly is not good for any engine -- car, truck, boat, snowmobile or whatever. And by all means check the oil before every trip and change oil frequently if the issue is chronic.

 

[SeaNymph Man]

Re: Fuel economy on 15 HP Merc four stroke,...what to expect?

I normally use the Yamaha web site for "rough" fuel consumption information since they have a very nice collection of performance tests for nearly any boat on the planet (or at least you can find one very like the one you are interested in) as well as fuel consumption, time to plane and rpm at given speeds. They do not list a 15 HP on a 14 foot boat but they do show a 20 HP. Even the 20 HP charts don't show fuel economy numbers because the consumption rate is too low for the test equipment they use. That is reasonable since most fuel flow monitors are of the turbine variety and require a certain flow rate to provide any reasonable accuracy. The only other way to do it is to monitor speed and rpm accuractely and simply run a given distance for a given at a given rpm and then measure the amount of fuel used. Way too tiime consuming for the number of boats and engine combinations available. Besides -- you own a boat. If you have to worry about fuel consumption it was not a wise investment. Your new boat will burn less fuel than the old one. The amount different will not amount to enough that a bulge develops in your wallet from fuel savings. As for the "making oil issue" that has nothing to do with the engine being on the water or in the garage. Making oil results from not getting the engine up in the rpm band often enough. Oil gets diluted with fuel from the very slow operating speeds caused by trolling for extended periods. To prevent or at least minimize this issue open the thing up now and then. Poking along constantly is not good for any engine -- car, truck, boat, snowmobile or whatever. And by all means check the oil before every trip and change oil frequently if the issue is chronic.

Thanks for the info,guys. The old 18 Evinrude was indeed a fuel hog on the
boat I have now(the one that is being traded for the new Lund). I expect the
15 Merc four stroke will burn far less fuel then. I guess I'll be going to anyone
of the three nearby reservoirs where I live; J.E. Roush,Salamonie,and Mississinewa where I will be able to open her up without fear of breaking 10 MPH speed limits on lakes I normally fish. And yes,the oil WILL be checked
prior to each trip. I seen a Tohatsu video on youtube where they suggested checking the oil when the engine is cold,rather than warm. I'll check my Mercury owner manual to see what it says for sure. Those three reservoirs will provide a good place to break it in.

 

[pecheux]

Re: Fuel economy on 15 HP Merc four stroke,...what to expect?

With a late model 15 hp 2 cycle OB hooked to a 14 footer fiverglass boat I regulary run approx 4 to 5 miles up the river (+ return) mostly WOT with periodic trolling and idling at fishing spots ... hardly ever stop the motor for a full 4 hours ... and use 2.5 to 3 gal of gas. I find it difficult to come up with precision on these small OB,s since they are more influenced by misc. factors than bigger motors. Perhaps you can use this data for comparisons when using your new 4 strokes motor. Cheers.