Unhappy with 2010 Merc 115hp 4-stroke

[Jer_H]

Hi all,

After working out most of the bugs with my new 17' Sylvan Expedition, I am less than happy with the fuel economy of the 115hp 4-stroke. The boat is a deep-V weighing 1220lbs dry, holds 90litres of fuel, 2 batteries, and very little gear onboard.

The dealer initially put a 15" pitch prop by accident which caused very high RPM's at mid throttle, and burning alot of fuel. After realizing their mistake, they have replaced it with a 21" P aluminum prop, and RPM's are about 5200 at WOT when trimmed to just before porpoising. Motor is rated at 5800-6400 full throttle.

I thought the new prop would improve the fuel consumption, but it hasn't. Last weekend I drove no more than 25mins across the lake, keeping it under 5000RPM putted around a bay, then 25mins back and went through over half a tank of gas?

Anyone with similar fuel consumption. Neighbours with same boat with a 115 2-stroke is burning less than half what I do? Suggestions?

Thanks in advance,

Jeremy

 

[milehighboater]

Re: Unhappy with 2010 Merc 115hp 4-stroke

According to Mercury you should be using just under 8 gallons per hour at 5000 rpm, which is about 30 leters per hour. Now is it sounds like you are using around 45 leters every half hour which is quite a bit of gas indeed, almost impossible. Now I am assuming you have a built in tank, there is a good chance if you are only using the fuel guage maybe it was not calibrated correctly and there is really more fuel in the tank than what it says. If you are getting that estimate by topping off the tank again then you may want to look for fuel leaks. For the motor to be burning 24 gallons of gas per hour is just not possible, not even for a poorly running 115hp.

 

[Blevins]

Re: Unhappy with 2010 Merc 115hp 4-stroke

I would say two things 30min at 5000rpm is a little much but youdhould be able to do what you want when you want. It would seem to mean that the motor just could not burn that much fuel. I have a 225hp carb on my 21' key largo and at plane around 3700 rpm I sip gas. Now wot she destroys gas but not that fast. I would assume you float level in your gas tank may be a little off but I assumed it worked as you trust it.

 

[clanton]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Its still propped wrong.

 

[Roodski]

Re: Unhappy with 2010 Merc 115hp 4-stroke

According to Mercury you should be using just under 8 gallons per hour at 5000 rpm, which is about 30 leters per hour. Now is it sounds like you are using around 45 leters every half hour which is quite a bit of gas indeed, almost impossible. Now I am assuming you have a built in tank, there is a good chance if you are only using the fuel guage maybe it was not calibrated correctly and there is really more fuel in the tank than what it says. If you are getting that estimate by topping off the tank again then you may want to look for fuel leaks. For the motor to be burning 24 gallons of gas per hour is just not possible, not even for a poorly running 115hp.

Milehighboater, I think you misunderstood his driving time, I believe it was 25 minutes each way, times 2, which would equal 50 minutes. If he's using over half his 90 litre tank, say 50 litres, that means he's using 1 litre/minute, or 60 litres/hour, which is exactly double the fuel he should be using. This is assuming he's accurate on how much fuel he's actually using.

 

[milehighboater]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Sorry about that, I think I was focused on the leter conversion. Still thats a lot of fuel. even at 16 gallons an hour, at least for a 115hp.

 

[Jer_H]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Regarding the prop, after checking the Merc Prop Selector, it looks like I should have a 19" P prop. My dealer will let me switch as it was their mistake.

Being new to all of this, I still have to check if the motor mount height, as it may be too low.

I'm fairly confident that the gas gauge is accurate as I have gone through 2 full tanks of gas already.

Does the motor run harder on fuel during the break-in period?

 

[Tig]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Its still propped wrong.

+1 Very wrong. You're motor is lugging and that is not going to be good for anything including fuel consumption. It's like driving a car around in too high a gear. I would drop the prop pitch and try to bring it up to the top of the operating range for WOT with average load.
That may help a bit even though it sounds like there may be more going on.

 

[Jer_H]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Am I correct with a 19" Pitch then?

 

[Tig]

Re: Unhappy with 2010 Merc 115hp 4-stroke

I was being a coward and not picking a pitch for you.
If you check out the sticky in the prop forum and post the information they ask for you will get the forum experts to recommend a prop.

My $.02
I don't think a 19 will get you into the range. I think 17 would make your boat get up and dance. I hear the number 200 RPM per inch of pitch used as a generalization. If so a 17 would get you to 6000 RPM. In reality I would expect even more because you would now be running in the peak power range for the motor.

 

[achris]

Re: Unhappy with 2010 Merc 115hp 4-stroke

Just on the fuel consumption.... My boat (heavy 20' cabin cruiser with a 220hp, Merc 4.3MPI sterndrive), at WOT/43knots (50mph) uses 60 litres/hour (that's just under 1.5l/nm, at cruising I'm using about 1.2l/hr)... The only true reading on fuel consumption is a flow meter, like I have... even if you refill the tank at the end of the day (and know exactly how much fuel you used) you have no real idea of actually how far you have travelled. How far is the other side of the lake? You say 25 minutes, at what speed? And how far did you go, and at what speed, 'just putting'?

Just with the info provided, 50 minutes at 5000rpm (and over-propped which will drive fuel consumption up), some (unknown) putting for 45 litres (was that a fill up or just off the gauge?).... sounds ok... not great, but ok.

Yes, new engine do use more fuel. Not a lot, but more.

Chris.........