fuel economy comparison

[weimy]

Is it normal for a 1995 175hp mercury black max to go through 42 gallons of fuel(at a wide range of rpm's) just as fast as a 1978 115hp johnson sea horse with 18 gallons of fuel (at a wide range of rpm's)?<br /><br />I upgraded boats and was shocked to find how much the mercury drinks gas. Any one with a little knowledge of both motors please let me know.

 

[WillyBWright]

Re: fuel economy comparison

I've never heard of an old 2-stroke Merc that was stingy on gas. If you want lotsa ponies, you gotta buy a whole lotta oats.

 

[JasonJ]

Re: fuel economy comparison

175 hosses is a bit more than a 115 in the power department, and without you having mentioned size, I can only assume the boat is larger. That punishing fuel consumption is what has kept me down in the sub 17 foot with 125 horse Merc. It is not exactly a fuel sipper, but I burn about 6 gallons on a good day of fishin' and that is acceptable to me (I never go above 3600 rpms, that is its optimal fuel consumption range). All I can say is keep the boat light and stay below 4000 rpms (as long as the boat is planing and is propped properly) and that will get you as good of economy as you are going to get.

 

[emckelvy]

Re: fuel economy comparison

Not sure, but wasn't the 115 HP V4 rated at the crank, while the later model V6 would have been rated at the prop. If this were the case, there'd be an even greater disparity between the two motors.<br /><br />Even on the same boat, you're talking a fair amount more weight in the stern to push around. And full throttle consumption on the 175 would be pushing 20 gallons per hour. <br /><br />Not to mention a V6 has more internal friction than a V4, FWIW. You also have to factor in the difference in cubic inches of displacement.<br /><br />Bet you've got a lot better hole shot, though! How many mph did it add to the boat's speed, or did you change hulls also? If not the same boat, it's extremely difficult to make a valid comparison.

 

[weimy]

Re: fuel economy comparison

thanks for the info it is a different boat a 1991 cajun 1900 tournament with a jackplate. It gets on plane great I think I'm going to purchase a high five prop for pulling skiers and fishing on no wake lakes. I will hope I can get on plane at a very low rpm.

 

[wrenchtrnr72]

Re: fuel economy comparison

my 150 merc will use about 1/8 tank of fuel iin 10 min. if i keep my foot in it! just like a vehicle when you put your foot in it your mpg goes way down, a boat is the same way, when you play you pay!!! and i'm not kidding.

 

[Mercury140-I6]

Re: fuel economy comparison

Picture this guys. Your car has 3-6 gears to keep the motor in it's optimum RPM range. In a boat, you have one gear. dive your car in first or second gear all day on the highway, and I'll just bet you will go through a whole bunch of fuel also. Add to that the fact that in a car, once you get going it doesn't need more than 50hp to stay at that speed (On level ground). In a boat, you are always fighting to stay up on plane. You have both gravity (Trying to drag you off plane), and drag to work against all the time. <br /><br />It take (X) amount of fuel to make (X) amoutn of hp. <br /><br />Or you can think about it this way. You get a 18' bow rider, and put on it a 90hp (To save fuel), and your friend gets the exact same hull and get's it with a 150hp. you are going to burn just as much in the 90 as you do in the 150 at the same speed, it's just the 90 will be at WOT and the 150 will be at cruise speed, but the 90 might not last as long as the 150 under those conditions.<br /><br />Just something to think about.<br /><br />Craig

 

[KCLOST]

Re: fuel economy comparison

2-stroke fuel consumption....<br /><br />HP/10 = Fuel Usage at WOT, per hour<br /><br />115/10 = 11.5 gallons per hr (WOT)<br />175/10 = 17.5 gallons per hr (WOT)<br /><br />That's a 52% increase in fuel usage when you changed engines. (however the hull change can also affect the numbers some)<br /><br />Fuel usage drops considerably at lower rpms however...

 

[emckelvy]

Re: fuel economy comparison

It's even worse than that, because the old HP/10 rule is for HP rated at the crankshaft.<br /><br />So, 175 HP at the prop is something closer to, let's say, 200 HP at the crank. That's why I was throwing around the 20 gph figure earlier.<br /><br />If the old V4 was rated at the crank the contrast between the 2 motors is even greater.<br /><br />And if the 115 was prop-rated you're still looking at a big diff as stated.

 

[Keith Buchanan]

Re: fuel economy comparison

Wow!! not one hour ago I went to juice up my car at the local petrol station and 95RON unleaded was £0.815 per litre so 17.5 gallons per hour as quoted by KCLOST would cost a packet.. Government fuel duty in the UK is frightening..<br /><br />Keith B....Keep it simple.

 

[KCLOST]

Re: fuel economy comparison

Sick!!! But hopefully not many of us run WOT for an hour straight... If I did I'd be fueling up at the lake every 1-1/2 hours.... And prices at the marina's are even more rediculous....

 

[Markzshark]

Re: fuel economy comparison

175 hosses is a bit more than a 115 in the power department, and without you having mentioned size, I can only assume the boat is larger. That punishing fuel consumption is what has kept me down in the sub 17 foot with 125 horse Merc. It is not exactly a fuel sipper, but I burn about 6 gallons on a good day of fishin' and that is acceptable to me (I never go above 3600 rpms, that is its optimal fuel consumption range). All I can say is keep the boat light and stay below 4000 rpms (as long as the boat is planing and is propped properly) and that will get you as good of economy as you are going to get.

Hi I've heard if you go over 4000 rpms you will double the fuel consumption. I'm about to put a 1992 135 Black max on a 18 ft pontoon. Has anybody else got a similar vessel running a 135 black max ?

 

[Faztbullet]

It will burn 13 gallon of fuel at WOT reducing RPM will decrease fuel burn slightly. I have a 1980 150 Johnson on my 24ft Lowes toon. It good decent fuel burn below 300Rpm but sucks it up when towing grandkids on tube/skis

 

[jbcurt00]

Hi I've heard if you go over 4000 rpms you will double the fuel consumption. I'm about to put a 1992 135 Black max on a 18 ft pontoon. Has anybody else got a similar vessel running a 135 black max ?

Please start a topic about your boat & motor combo and ask questions there.

Its been 17yrs since this topic was started and covers a different setup then yours.

Closed