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What is good or bad 'MPG" for an engine?


Hoffer

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I will probably be able to answer this question later this month. I am going to have a new depth finder installed where I should be able to calculate my miles driven from my depth finder and then see how much gas I have used and make the calculation.

But for now...what is a good - or even bad MPG for an engine??

I have a 2003 mercury 2 stroke - 75HP. (3 cylinder).

I know on our Spring trip it takes about 7 to 8 gallons of gas to drive the 18 miles to the resort. However, on that trip we are also loaded down with gear and everything - extra gas etc...

So that calculates out to roughly 2.5 MPG.

I am imagine when we are running around after we get there with just normal gear - maybe it goes up to 3MPG?

I normally also go through about 45 gallons on the trip. Sometimes more. So, that equates to about 135 nautical miles driven on each trip or so.

Anyway, 3MPG doesnt seem to be too great to me? I hopefully will be able to dial this in better once I get the new finder on this Spring. But how does that compare to what you guys see on your engines for MPG?

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that does seem a little excessive. i found a comparison test online of a few motors and thought i would share this one as its similar to my setup.

this motor is a 115 evinrude 2 stroke gallons per hour @ rpm

[email protected] [email protected] [email protected]

it said top speed of the boat they tested was 44 mph. so even at WOT still getting 4 mpgs. the other brands of motors in this class had similar numbers.

after looking at these numbers i will definetely back the throttle off a bit!!

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I have only measured 1 time, and it has been years ago, but I am running an Alumacraft 175 Tournament Pro with a Yamaha F115, and it was in the upper 8 mpg, mostly mid throttle driving.

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I get 6.5-7.5 mpg on my Yamaha 75 4S EFI at 4000 RPM's (on a 1625 Rebel XL). At WOT I get maybe 5. I have the engine linked up to my HDS 7 with the NMEA 2000 network, so MPG is always displayed (along with a bunch of other stuff).

I go through less than half the gas than I did with my old '84 Evinrude 90 hp carb'd 2S. So your 2.5-3 mpg sounds about right if you are talking running at wide open throttle trimmed out. I'm sure you'd hit 3.5 or even 4 if you backed it down to a few hundred RPM's over planing speed.

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why are you guys getting on him when he is just curious at to what approximately his MPG is? I like to just think that my MPG at full throttle is approx. 2-4 MPG. Is it better or worse I don't know as I have never officially checked it.

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Thanks. I was kinda wondering the same thing?

I thought these forums were to share and learn and ask questions. It must not be a crazy question since some know their MPG exactly with the hook up to the finders and satellites. So it must be something others want to know as well.

I have always wanted to know - at least be close to a good guestimate. Many things come to mind why. For example,If I knew my approximate MPG I can look at the gas used on a trip and see approximately how many miles I traveled on that trip. Its just fun stuff to know thats all. Hopefully in a few weeks I will have the new system hooked up and will be able to know once and for all. For those of you that posted some feedback - I appreciate your help! Good fishing to you. smile

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I think efficiency is important. Just because you are out fishing, doesnt mean you need to be wasteful. I see it no different then asking what someone is averaging in their truck.

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I am definitely going to back off full throttle as well!

I also do a lot of trolling with the motor. Just like 3 mph trolling deep diving plugs. I wonder if this has a negative effect on MPG or possibly positive?

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You cannot use mpg and apply it across the board but it can be used as a very rough estimate. Reason, each boat is different. Its hull design, weight, length, width, material, etc. Each has its own different cruising speed. A heavier boat and deeper v boat will create more drag and burn more gas vs one that is lighter or one that has a shallower hull, etc.

Not real numbers but a good logical example of a 115hp Yamaha 4 Stroke apply to several different type of boats.

17' Deep V Aluminum boat = @ 33mph, efficiency is apx 6.8mpg

17' Bass Boat = @ 34mph, efficiency is apx 8.8mpg

17' Pontoon = @ 17mph, efficiency is apx 2.5mpg

20' Flat bottom Jon Boat= @ 29mph, efficiency is apx 9.2mpg

To answer your question, if you're getting 5 mpg +, its pretty darn good.

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How do did you come up with those numbers?

I would think that a given motor would burn the same amount of fuel per hour at WOT, no matter the speed driven. This is assuming that the rpms are set level between them.

Therefore, if you get 6.8mpg in one boat at 33mph, you should get 7.00mpg in a different boat going 34mph.

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How do did you come up with those numbers?

I would think that a given motor would burn the same amount of fuel per hour at WOT, no matter the speed driven. This is assuming that the rpms are set level between them.

Therefore, if you get 6.8mpg in one boat at 33mph, you should get 7.00mpg in a different boat going 34mph.

These are rough estimates of previous boats I've owned and friends. Again, they're not real numbers but the point is, each boat, hull, design and weight makes a difference.

So you're saying if a motor rated 7.0mpg, I can slap that onto any type of boat, doesn't matter its weight and length and still get 7.0mpg? That's like saying, if I swapped toyota prius motor into a Chevy Canyon I will still get the same fuel efficiency?

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How do did you come up with those numbers?

I would think that a given motor would burn the same amount of fuel per hour at WOT, no matter the speed driven. This is assuming that the rpms are set level between them.

Therefore, if you get 6.8mpg in one boat at 33mph, you should get 7.00mpg in a different boat going 34mph.

I'm pretty sure if you strapped my 90-hp Merc onto the back of the Queen Elizabeth 2 and ran it at WOT, you wouldn't get the same mpg as it does on my 16' tin boat crazy

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I am definitely going to back off full throttle as well!

I also do a lot of trolling with the motor. Just like 3 mph trolling deep diving plugs. I wonder if this has a negative effect on MPG or possibly positive?

Generally I get 3.5-4 mpg at trolling speed. Although it doesn't use much gas at forward idle, it takes just as much gas to keep the engine running as it does to propel you forward.

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Ive got a 175 vrod w smart craft gauges that gives me gph. Assuming i can convert correctly with my speed i get about 5mpg at cruising speed (30-35) and about half that at wot ~50.

Forgot, thats a deep v glass boat

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From what you guys are quoting me - I think I am probably in the ballpark of what is considered "OK". I was always curious to know if my engine was performing worse, average or better.

I am thinking by the time I get a normal load in the boat - I should be around 4 at WOT and probably 5 at a little less. Hopefully I get the new unit on the boat before I head up for my week long trip and if so, I will report back here with what I found out for MPG. Oh yes, I think I mentioned 75HP merc 2 stroke - but it pushes a 1650 Crestliner Fish hawk

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These are rough estimates of previous boats I've owned and friends. Again, they're not real numbers but the point is, each boat, hull, design and weight makes a difference.

So you're saying if a motor rated 7.0mpg, I can slap that onto any type of boat, doesn't matter its weight and length and still get 7.0mpg? That's like saying, if I swapped toyota prius motor into a Chevy Canyon I will still get the same fuel efficiency?

I didn't say that.

What I was saying is that I expect a motor will burn the same amount of fuel per hour at WOT no matter what boat it is on, assuming it is proped correctly. Giving you two constants, fuel burned and time. Add in the variable of speed and you get the formula below.

A 90 horse will burn say, 7 gallons an hour no matter if it's on a 14' tin boat or the QEII. One will cover a lot more ground.

Therfore, 34mph X 6.8mpg / 33mph = 7.0mpg. That says that a motor that does 6.8mpg at 33mph on one boat would get 7.0mpg at 34mph when hung on a different boat.

That is different than what you posted which makes me think the comparison is with different motors on different boats.

Or I'm completely missing something. That's why I asked.

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