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mercury 60 hp bigfoot info-gas usage

papyson

papyson

Outstanding Contributor
i have a new 50hp bigfoot mercury 4 stroke that is about 10 months old...every fall i fish one spot thats about a 10 mile run each way...2 trips per day....i noticed gas usage was high...higher than it ever was on a 90 evinude that i run for 18+ years to this same spot... after thinking about it i begin to think maybe it was the higher rpm i was turning on this particular run....i looked it up on the mercury site and sure enough there is a drastic difference between 4k rpm and 5.5 or higher rpm....so i slowed it down to 5k tops and the gas mileage got back in line....this is for info only...the motor is correctly propped....the fact is (on this model at least) is that a 4cycle at top rpm drinks the gas...and its hard as hell to make a long safe run with it throttled back...especially when you are used to the sound of a 2cycle pounding away back there..
 
Yes, you have uncovered one of the great MYTH's that 4 strokes are sooooooooooo much easier on gas.

They are, but only below 3500 rpms (give or take depending on the model) - no dealer is too quick to point out that fact. So if you plan on trolling all day, then yes, a 4 stroke will save you significant gas (close to double compared with a 2 stroke) - but tap up that throttle and the playing field is even.

When you "open up" any outboard to it's wide open throttle (WOT) range, it will, on average, burn 1 gallon per hour for every 10 horses whether it's a 2 stroke, a 2 stroke Direct Inject or a 4 stroke (so your 60 would burn 6 gallons per hour).

The Bigfoot models compound this problem because they were designed for pushing heavier weights at lower speeds (like pushing a pontoon or a workboat) such that the lower gears means that the motor doesn't work as hard down low in it's torque band, but you need significantly more rpms to achieve the same "speed" as a 60 horse that is "non-bigfoot".

(A bigfoot will push a heavy load burning less gas than a non-bigfoot of the same horsepower because you would have to increase the rpms of the non-bigfoot to obtain the same torque as the bigfoot produces at lower rpms)

So while your bigfoot, opened up, makes say 32 mph burning 6 gph (and I'm just guessing at a top speed, but the difference will be correct), a non-bigfoot 60 would get you an extra 4'ish mph.

Or, to put it another way that's easier to understand - bigfoot, 5.3 mpg - non-bigfoot 6 mpg in the same horsepower (12% difference in gas mileage but the bigfoot still producing 40% more torque than the non-bigfoot at wot - and if the load is heavy you "want" that)
 
Graham....you are right on ....i have a 10 min idle out of my camp to open water and once i finish the run to the lake i slow down running the shoreline...this is in addition to the run i called 10 miles..so its hard to calculate...but the open run is 25-30 minutes...running a 5 degree 17 foot aluminum bass boat that is fully decked and outfitted..100 gauge aluminum...its heavy.....i am going to run it below 5k rpm if possible...i will say the dealer didnt specify gph or mpg but he kept mentioning 4k rpm... to be honest i cant see a 4 cycle having a long life span at 6k anyway..maybe a honda but not a merc...i would have bought a honda if there was a dealer in the vicinity of my camp....the yammy dealer blew a sale years ago with me when i went in dressed like a bum and was treated as such...
 
Papyson
What prop are you running? I have the same motor. It spent its first 5 years hanging off the back of a house boat. I now am really pleased with its performance on my 17ft aluminium xwntre console. I have the problem that the motor is "making oil". The level in the sump rises after long periods of idle, and the oil smells like gasoline. I thought at first that it was a headgasket problem , but then read that this model is a bit prone to having gas get past the rings at isle. aWhen I give the motor a proper run the gas comes out of the oil.
so back to my question what prop do you run? What type/size boat
Jim
 
the boat is in the previous entry....i will have to look at the prop....the motor is less than a year old with lower than usual hours for me but so far no problem as you described...the commercial fishermen are running this motor down here and i have heard no complaints...once i set my trim when i put it in the water i dont have to touch it all day unless i fish in cover and trim it up...out of the hole good and everything with the trim set at running speed..in gear at low idling or a little better rpms it makes all kind of noises but thats common with the mercs....my camp is on the water in a no wake zone and i can hear them all...i read somewhere that there is a fix for that on the larger hp engines..something to do with the prop...its not hurting anything so i dropped pursuit of the problem...i have read on here about some oil pump problems but so far so good....
 
i am going to check my oil a little closer in the future for gas...in your case this needs fixing or the motor will not last in my opinion...
 
Papyson
thanks for the info on the prop. you are right about it being worrysome about the fuel getting into the oil. I have lost the reference but when i first found the problem. after much trolling and using the boat for training, I found entries on the internet discussing the problem as if if were common with the 4st 60 of the mid 2000 years make.
Dont know how to correct it. but do know that if I bring the motor up to 400 or more for 10 minutes the problem goes away. evaporates the gas back out of the oil and burns it .
Jim
 
Let's see - if we "decode" that prop I believe it to be a 3 blade, right hand rotation (normal rotation), 13 1/2" diameter, 13" pitch (power tech puts the pitch first in their model numbers) which would fall right into Merc's "generic" recommendation for that motor when mounted on a 17-20' boat.
 
correct...the boat is 17 foot but everything including the decking and floor is 100 gauge aluminum...its a heavy 17 footer...the boat is 19 years old this month and i just spent money re-carpeting and stuff...life time boat unless it falls off the trailer...i tried the fiber glass route when i first retired 21 years ago but was spending more time keeping it clean and shiny than i was fishing...what do you think about his problem with getting gas in the oil ?
 
There is one or two mechanical problems that could cause this BUT, here's an explanation that applies in most cases (sorry, can't remember the source to give proper credit)....

This is referred to as "Making oil". Here it is in a nutshell. Water vapor enters the crankcase of all motors from the atmosphere, and as a by-product of combustion. In other motors, the oil gets rather hot and any water vapor that may condense will steam-off and exit the crankcase breather. 4-stroke outboard motor oil doesn't get nearly as hot, so the water just keeps on collecting.

Tiny amounts of raw fuel also leak into the crankcase on the compression stroke, potentially diluting the oil and raising the level on a cool-running motor. Or there could be a fuel system leak. Typically the odor of the latter situation is fairly obvious, but not necessarily. Lack of a gassy smell shouldn't preclude checking the possibility of fuel system leaks. Over choking and frequent flooding will also cause fuel to get into the oil......


If you do a websearch on "making oil" you might find the entire dialog..
 
Thanks, that is what i found when I searched the internet. my first reaction to discovering that I was making oil was that I had a head gasket letting water into the oil, but when i am careful to run the motor up to speed for a while. it cooks the water/fuel out of the oil. a number of mechanics have warned that a fuel pump diaphram leak could show the same effect.
Jim
 
Graham...have experienced with gas usage on that same run on about 8 round trips...six trips alone with gear and 2 trips with additional 200 pound man and his gear...dropping to 4500 rpm max makes the gas usage acceptable but not great... if i had it to do over i would not buy the bigfoot...my thinking was i was getting a heavier built lower unit such as the ones that were put on ''industrial'' engines years ago...thats not the case....this motor just changes gear ratios... the actual usage is 3 gallons each trip at lower rpm....the 90 evinrude it replaced would run wide open on 4 gallons...4500 is about as slow as i can make myself run....
 
Lesson learned. Yes, the bigfoot really is primarily just different gears.

Hey, just take it slow and enjoy the scenery and the relaxing ride (unless of course the weather gets nasty - then you can complain about the extra fuel "after" you get back on dry land :))
 
I also have a 17 ft aluminium centre console and a 60 efi merc 4 st. it is so fast that I havn,t had it to 5000 yet, most of my cruising is at abour 3800 and then I am going 18 knot. It is a tri hull or cathedral hull and traps air onder it. was first fitted with an inboard motor and a jet. then a professional job put a pod on the back and the 60 on it. feels really loose when it is planing, and I am always in the ocean so its never all that smooth. so I agree slow down and smell the oysters.
Jim
 
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